1328.     Consistent Automated Planning of Irregular ROI’s for Intracranial MRA MIP’s

Chiel J. den Harder¹, Elizabeth A. Moore¹, Arianne M. van Muiswinkel¹

¹Philips Healthcare, Best, Netherlands

MIP’s of intracranial MRA’s require definition of regions of interest (ROI’s). Drawing ROI’s manually can be tedious and error-prone. Alternatively, using automated segmentation to consistently define ROI’s doesn’t allow for user preferences about shape and position of ROI’s.

                  1329.     Studying the Hemodynamics in Cerebral Arteries Using Image-Based Computational Fluid Dynamics and 4D Phase-Contrast Magnetic Resonance

Juan R. Cebral¹, Christopher M. Putman², Marcus Alley³, Roland Bammer³, Fernando Calamante^4,5

¹Computational and Data Sciences, George Mason University, Fairfax, VA, USA; ²Interventional Neuroradiology, Inova Fairfax Hospital, Falls Church, VA, USA; ³Department of Radiology, Stanford University, Stanford, CA, USA; ⁴Brain Research Institite, Florey Neurosciences Institutes (Austin), Melbourne, Victoria, Australia; ⁵Department of Medicine, University of Melbourne, Melbourne, Victoria, Australia

Studying the hemodynamics in cerebral arteries using image-based computational fluid dynamics and 4D phase-contrast magnetic resonance

                  1330.     A New Method for Selective Dynamic MRI Angiography Using Arterial Spin Labeling

Tom Okell^1,2, Matthias Guenther³, David A. Feinberg⁴, Peter Jezzard¹

¹FMRIB Centre, University of Oxford, Oxford, Oxon, UK; ²Churchill Hospital, Oxford, Oxon, UK; ³University of Heidelberg, Germany; ⁴Advanced MRI Technologies, CA, USA

In this study we demonstrate for the first time a new method for non-invasive selective dynamic angiography using the principles of arterial spin labeling (ASL). A pseudo-continuous ASL labeling module was inserted in front of a low flip angle flow-compensated cine angiographic readout module. This allows selective labeling and visualization of the major feeding arteries to the brain, analogous to the invasive alternative method of intra-arterial x-ray digital subtraction angiography. The new method has potential applications in a number of cerebrovascular diseases, such as carotid or vertebral stenosis, arterio-venous malformation, and stroke.

                  1331.     MRI Assessment of Blood Flow Artifacts in a Transgenic Mouse Model of Alzheimer’s Disease

Firat Kara¹, Janneke Ravensbergen¹, Niels Braakman¹, Mark A. van Buchem², Reinhard Schliebs³, Huub J.M. de Groot¹, A Alia¹

¹Leiden Institute of Chemistry, Leiden University, Leiden, P.O. Box 9502, Netherlands; ²Department of Radiology, Leiden University Medical Center, Leiden, Netherlands; ³Paul Flechsig Institute for Brain Research, University of Leipzig, Leipzig, Germany

It is well known that vascular abnormalities coexist with other pathological features of Alzheimer’s disease (AD). In this study we applied high resolution MRA at 9.4T to compare the vascular architecture of living APPTg2576 transgenic and control mice. Due to high field strength and use of strong gradients, the large and medium sized arteries were very clearly imaged. Flow voids were observed at different places such as in superior cerebral artery, anterior cerebral arteries as well as in pterygopalatine arteries. Our results suggest that MRA at high magnetic field is useful method to monitor blood flow defect in mouse models of AD.

                  1332.     In Vivo Visualization of Brain Tumour Angiogenesis Using 3D δR2-Based Microscopic MR Angiography (3DδR2-MMRA)

Chien-Yuan Lin^1,2, Ming-Huang Lin², Sui-Shan Lin², Yu-Ying Tung², Jyh-Horng Chen¹, Chen Chang²

¹Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan; ²Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan

Tumor-associated microvascular changes offer important new insight into how tumors grow and respond to treatment. This study was aimed to simultaneously assess the changes of microvascular morphology and function on ethylnitrosourea(ENU)-induced rat brain tumor model at different stages using 3D £GR2-Based Microscopic MR Angiography (3D£GR2-mMRA).

                  1333.     Comparison of Hypercapnia- And Hyperoxia-Induced Blood Flow Changes in the Retina Detected by MRI and Laser Speckle Imaging

Haiying Cheng¹, Yumei Yan¹, Yingxia Li¹, Timothy Q. Duong²

¹Yerkes Imaging Center, Emory University, Atlanta, GA, USA; ²Research Imaging Center, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA

We recently reported blood-flow (BF) MRI of the rat retina at 90x90x1500-m;m resolution. We found that hyperoxia decreased blood flow relative to baseline (air) and hypercapnia increased blood flow. BF measurements of physiologic stimuli in the retina are sparse due to a lack of reliable blood flow imaging techniques to study the retina. Available data indicated that hypercapnic responses in the retina are controversial with some reporting no changes and others reported significant changes. To corroborate our MRI findings, we developed and applied a novel laser speckle imaging to measure BF in the rat retina under identical experimental conditions.

                  1334.     4D Velocity Measurements in an Intracranial Aneurysm Using 3T Phase Contrast Angiography

Pim van Ooij¹, Joppe J. Schneiders¹, Marieke E.S. Sprengers¹, Ed van Bavel², Aart J. Nederveen¹, Charles B.L.M. Majoie¹

¹Radiology, AMC, Amsterdam, Noord - Holland, Netherlands; ²Biomedical Engineering & Physics, AMC, Amsterdam, Noord - Holland, Netherlands

4D velocity measurements using phase contrast angiography can be a useful tool to diagnose patients with neurovascular diseases. In this study velocity in an intracranial aneurysm is measured. The treatment of intracranial aneurysms is invasive and risky, so more knowledge on the factors that contribute to aneurysmal rupture is needed. In this study it is shown that when the aneurysm is large enough, clinically relevant velocity profiles can be measured using phase contrast angiography, which can serve as a validation of computational flow dynamics, or used as boundary conditions.

                  1335.     Assessment of the Neovascularisation of Carotid Atherosclerotic Plaque in Symptomatic Patients at 3T by DCE-MRI: Feasibility Study

N. Jane Taylor¹, Vicky J. Goh¹, J James Stirling¹, Ian Simcock¹, Matthew Orton², David J. Collins², Ralph Strecker³, Leon Menezes⁴, Justin Cross⁵, Carl W. Kotze⁶, Syed W. Yusuf⁶, Ashley M. Groves⁴

¹Paul Strickland Scanner Centre, Mount Vernon Hospital, Northwood, Middlesex HA6 2RN, UK; ²CR-UK Clinical MR Research Group, Royal Marsden Hospital, Sutton, Surrey, SM2 5PT, UK; ³Healthcare Sector, Siemens AG, 91052 Erlangen, Germany; ⁴University College Hospital, London, UK; ⁵Addenbrookes Hospital, Cambridge, UK; ⁶Brighton and Sussex University Hospitals, Brighton, UK

The purpose was to prospectively assess the neovascularisation of symptomatic carotid plaques using DCE-MRI at 3T. 9 patients (8 male; mean 71 years) presenting with transient ischaemic attack, with significant stenoses on Doppler ultrasound and awaiting carotid endarterectomy underwent 3T DCE-MRI following injection of 0.1mmol/kg Gd-DTPA (dynamic 3D VIBE sequence, 5.3s interval, 70 acquisitions). Semiquantitative (IAUGC₆₀; peak gadolinium concentration (mmol); time to peak (s), maximal gradient) and quantitative (K^trans, v_e, k_ep, v_p) parameters were obtained following motion correction and image registration. Mean K^trans, v_e, k_ep were 0.74, 0.28, 2.33 respectively. 3T DCE-MRI plaque assessment is feasible.

                  1336.     The Role of 4D MRA with Keyhole and View-Sharing at 3.0T in the Diagnostic Work-Up of Cerebral Arteriovenous Malformations: A Prospective Intra-Individual Study

Dariusch Reza Hadizadeh¹, Guido M. Kukuk¹, Jürgen Gieseke^1,2, Gabriele Beck³, Liesbeth Geerts³, Julia Bergener¹, Azize Boström⁴, Johannes Schramm⁴, Horst Urbach¹, Hans Heinz Schild¹, Winfried Albert Willinek¹

¹Radiology, University of Bonn, Bonn, NRW, Germany; ²Philips Heathcare, Hamburg, Germany; ³Philips Healthcare, Best, Netherlands; ⁴Neurosurgery, University of Bonn, Bonn, NRW, Germany

The combination of keyhole, CENTRA, parallel imaging, partial Fourier, and view-sharing allows for high spatial and sub-second temporal resolution 4D MRA with whole head coverage. 4DMRA was evaluated in the entire diagnostic work-up of patients with cerebral arteriovenous malformations (cAVM) including pre- and post-operative assessment and was compared to digital subtraction angiography (DSA) in 38 consecutive patients. Highly accelerated 4DMRA matched with DSA in all patients regarding pre-operative Spetzler-Martin Classification and post-operative residual filling and may be considered a non-invasive alternative in the diagnostic work-up of patients with cAVM.

                  1337.     Quantitative MR Perfusion in Patients with Intracranial Arteriovenous Malformations: Utilizing Spin-Echo Sequences to Characterize Vascular Steal

Christopher Sean Eddleman¹, Jessy J. Mouannes², Anindya Sen³, Guilherme Dabus³, Christopher C. Getch, Bernard R. Bendok³, Hunt H. Batjer, Timothy J. Carroll³

¹Neurological Surgery, Northwestern University, Chicago, IL, USA; ²Biomedical Engineering, Northwestern University; ³Radiology, Northwestern University

Intracranial arteriovenous malformations (iAVMs) are high-flow AV shunts that can affect perfusion of surrounding normal brain. Although controversial, vascular steal is thought to contribute to the risk of normal perfusion breakthrough. Knowledge of specific areas of vascular steal could alter endovascular and surgical strategies of treatment. Spin-echo perfusion acquisitions allow detailed mapping of areas of vascular steal in patients with iAVMs.

                  1338.     Evaluation of Blood Flow from STA-MCA Bypass by MRA with Off-Sagittal Saturation Pulse

Toshiaki Akashi¹, Toshiaki Taoka¹, Hiroyuki Nakagawa¹, Toshiteru Miyasaka¹, Masahiko Sakamoto¹, Satoru Kitano¹, Satoru Iwasaki², Kimihiko Kichikawa¹

¹Radiology, Nara Medical University, Kashihara, Nara, Japan; ²Radiology, Higashiosaka City General Hospital, Higashiosaka, Osaka, Japan

We evaluated the feasibility of MRA with off-sagittal saturation pulse covering STA and bypass point (sMRA) for discrimination between antegrade flow from ICA and bypassed flow from STA. Conventional MRA (cMRA) and sMRA were obtained. sMRA demonstrates only antegrade flow because off-sagittal saturation pulse suppress signal of bypassed flow while cMRA shows both of antegrade and bypassed flow. Subtracting source images of sMRA from those of cMRA was able to give source images and MIP images demonstrating bypassed flow with suppressed antegrade flow in most cases. sMRA is feasible technique for the post-operative assessment of STA-MCA bypass function.

                  1339.     Evaluation of Perforating Arteries Originating from the Posterior Communicating Artery at 7 Tesla MRI

Mandy M. Conijn¹, Jeroen Hendrikse, Jaco J. Zwanenburg², Taro Takahara, Mirjam I. Geerlings³, Willem P. Mali, Peter R. Luijten²

¹Radiology, University Medical Center Utrecht, Utrecht, Netherlands; ²Image Sciences Institute, University Medical Center Utrecht; ³Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht

This is the first study to date that utilized the increased sensitivity of 7 Tesla MRI to study the anatomical variability of small, normally non-detectable, arteries in the brain. With angiography at 7T we could clearly visualize the deep perforating arteries branching from the posterior communicating artery (PCoA) without use of contrast agents. We found a high prevalence of visible perforating arteries branching from the PCoA, and an association between the diameter of the PCoA and the presence of a perforator. Furthermore, we found a significant correlation between the left sided and right sided anatomy of the posterior circulation.

                  1340.     Assessing Cerebrospinal Fluid Flow in the Brain Using 3D Phase Contrast Velocity Encoded MRI

Henrik Odéen¹, Michael Markl², Bruce S. Spottiswoode³

¹Lund Institure of Technology, Lund University, Lund, Sweden; ²Diagnostic Radiology, Medical Physics, Albert-Ludwigs Universität, Freiburg, Germany; ³Cape Universities Brain Imaging Centre, Cape Town, South Africa

This work describes the application of 3D velocity encoded MRI to assess CSF flow patency in the brain. Five normal volunteers were scanned using a time-resolved 3D gradient echo phase contrast sequence with 3-directional velocity encoding. Post processing involved spatiotemporal phase unwrapping, fitted field inhomogeneity surface subtraction, and combining data from the three velocity encoding directions into a 3D integrated flow volume. Communicating flow between ventricles and passageways was then identified using nearest-neighbour connectivity. Flow connectivity within the brain was demonstrated in all five volunteers. This technique provides an automated and promising means of assessing CSF flow patency.

                  1341.     Is Flow Rate or Stroke Volume Better for the Assessment of CSF Flow in NPH?

Mario Forjaz Secca^1,2

¹Cefitec, Physics Department, Universidade Nova de Lisboa, Monte de Caparica, Portugal; ²Ressonancia Magnetica - Caselas, Lisboa, Portugal

Two different parameters have been used in the assessment of abnormality in the flow of CSF at the Aqueduct for NPH (normal pressure hydrocephalus): Stroke Volume and Flow rate, which can lead to contradictory results. Since both can be calculated easily from the same data, we evaluated which would be the best parameter to take into consideration. By analyzing the data from 580 patients and studying of the variation of both values with heart rate on volunteers we found that FR, leading to less abnormal cases and being less sensitive to heart rate, is a better parameter to evaluate NPH

                  1342.     MR Arterial Spin Labeling and Spectroscopy in Patients with Symptomatic Internal Carotid Artery Occlusion

Jie Lu¹, Kuncheng Li, Miao zhang

¹Xuanwu Hospital, Capital Medical University, Beijing, China

ASL is a non-invasive method to quantitatively measure perfusion without contrast material. MRS can non-invasively identify cerebral abnormal metabolism. Patients with symptomatic occlusion of the internal carotid artery (ICA) with compromised cerebral blood flow (CBF) and decrease N-acetyl aspartate (NAA) are at risk for future ischemic infarcts in the brain. In this study, we characterized CBF and the concentrations of choline, creatine, and NAA changes in cerebral white matter in patients with symptomatic ICA occlusion. Our result suggested ASL and MRS may provide a convenient, inexpensive, noninvasive method for identifying ICA occlusion patients at risk for future stroke.

                  1343.     Feasibility of Imaging Mesenchymal Stem Cells in Vitro Using Standard MRI Sequences

Emidio Tarulli¹, Voytek Gretka², Amy Hoyles³, Cindi Morshead³, Greg J. Stanisz²

¹Department of Medical Biophysics, University of Toronto, Toronto , ON, Canada; ²Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada; ³Department of Surgery, University of Toronto, Toronto, ON, Canada

While stem cell therapies of stroke have shown success in structural and functional recovery of lost tissue, the ability to track cell migration and distribution in a non-invasive manner remains a work in progress. This study demonstrates the ability to track single rat mesenchymal stromal cells (rMSCs) labeled with micron-sized superparamagnetic iron-oxide (MPIO) particles (Bangs Labs, MC05F) with standard MRI sequences in vitro.

                  1344.     Limitations of Iron-Based Stem Cell Tracking in MRI-Monitoring of Stem Cell Therapies in Vivo

Emidio Tarulli¹, Voytek Gretka¹, Amy Hoyles², Cindi Morshead², Greg J. Stanisz¹

¹Department of Medical Biophysics, University of Toronto, Toronto, ON, Canada; ²Department of Surgery, University of Toronto, Toronto, ON, Canada

This investigation makes use of

                  1345.     Novel Combination Therapy of Recombinant Annexin 2 and Low Dose Recombinant Tissue Plasminogen Activator in Embolic Rat Stroke Model: A Magnetic Resonance Imaging Study

Yoji Tanaka¹, Tsukasa Nagaoka¹, Govind Nair¹, Qiang Shen^1,2, Xiaodong Zhang¹, Timothy Q. Duong^1,2

¹Yerkes Imaging Center, Yerkes National Primate Research Center, Emory University, Atlanta, GA, USA; ²Research Imaging Center, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA

In the treatment of acute phase ischemic stroke, tPA has high risk of hemorrhage which is usually fatal, and the treatment time window is very narrow. The aim of this study is to examine a novel combination therapy of recombinant annexin 2 and low dose rtPA for acute ischemic stroke with employing MRI. We conclude that the combination therapy has a possibility to reduce the harmful side effect of rtPA without reducing its benefits as treatment.

                  1346.     Effect of NBO Treatment on Lesion Volume at Early and Late Reperfusion Time Points After Transient Focal Cerebral Ischemia

J Ramu¹, W Liu¹, KJ Liu¹, R Sood¹

¹Neurology, University of New Mexico, Albuquerque, NM, USA

The goal of this study was to compare the effect of NBO treatment on the lesion volume between early and late reperfusion time points in a rat model of middle cerebral artery occlusion (MCAO).

                  1347.     Aging and Hypertension Increase the Susceptibility of Brain Tissue to Ischemic Injury: Animal Brain MR Imaging Study

MeiYu Yeh¹, Tsong-Hai Lee², Ho-Ling Liu^3,4

¹Department of Medical Imaging and Radiological Sciences, Chang Gung University,, Kwei-Shan , Tao-Yuan, Taiwan; ²Stroke Section, Department of Neurology and Stroke Center,, Chang Gung Memorial Hospital, Kwei-Shan , Tao-Yuan, Taiwan; ³Department of Medical Imaging and Radiological Sciences, Chang Gung University, Kwei-Shan, Tao-Yuan, Taiwan; ⁴MRI Center, Chang Gung Memorial Hospital, Kwei-Shan , Taoyuan, Taiwan

Age is the most important non-modifiable risk factor for stroke and it is estimated that the stroke rate is doubled each 10 years after age 55. Diffusion- and perfusion-weighted magnetic resonance imaging (DWI and PWI, respectively) can provide a simple and feasible method to investigate the ischemic brain tissue at risk for infarction in the acute stage of stroke. Our study suggests that the reason for aging and hypertension to be the most significant risk factors for stroke is possible that they may increase the susceptibility of normal brain tissue to ischemic injury by influencing the cerebral diffusion and perfusion.

                  1348.     Temporal MRI Profile of Hermorrhagic Transformation After Embolic Stroke in Spontaneously Hypertensive Rats

Ivo Adriaan Carol Willem Tiebosch¹, Annette van der Toorn¹, René Zwartbol¹, Mark Jacobus Rosalie Joseph Bouts¹, Ona Wu², Rick Michiel Dijkhuizen¹

¹Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands; ²Athinoula A. Martinos center for biomedical imaging, Massachusetts General Hospital, Charlestown, MA, USA

Thrombolytic treatment after acute ischemic stroke increases risk of hemorrhagic transformation (HT), however, the pathological basis thereof is largely unresolved. We applied multiparametric MRI to assess the temporal profile of pathophysiological processes associated with HT after embolic stroke in spontaneously hypertensive rats. Selective regions within the ischemic lesion displayed HT after 7 days. These regions were characterized by significantly reduced perfusion, increased blood-brain barrier leakage and prolonged T2 within 24 h after stroke. This indicates that multiparametric MRI may provide a powerful tool to assess risk of HT after stroke in treated as well as non-treated subjects.

                  1349.     Multiparametric MRI Correlation with Tissue Outcome in Early Phase of Acute Ischemic Stroke in Rats

Kimmo Jokivarsi¹, Yrjö Hiltunen², Risto Kauppinen³, Olli Gröhn¹

¹Department of Neurobiology, University of Kuopio, Kuopio, Finland; ²Department of Environmental Science, University of Kuopio, Kuopio, Finland; ³Biomedical NMR Research Center, Dartmouth Medical School, Hanover, NH, USA

We investigated the prediction power of different combinations of MRI parameters in rat middle cerebral artery occlusion model. We show that by using three to four MRI contrasts (including diffusion, T2, T1r and perfusion) in combination, correlation ranging from 0.64 to 0.80 with the histological outcome is achieved. The correlation depends on brain region and age of lesion. Our data suggest that MRI may predict ischemic lesion expansion and fate of tissue at risk of stroke in a clinically useful manner.

                  1350.     Late Stimulation of the Sphenopalatine Ganglion in Ischemic Rats Improves NAA Levels and DWI Characteristics

Amnon Bar-Shir¹, Noam Shemesh¹, Revital Nossin-Manor², Yoram Cohen¹

¹School of Chemistry, Tel Aviv University, Tel Aviv, Israel; ²Diagnostic Imaging, The Hospital for Sick Children, Toronto, ON, Canada

The present study longitudinally examines the effect of SPG-stimulation of ischemic rats on NAA levels, DWI characteristics and behavioral tests. It was found that SPG-stimulation treatment of rats after 2h of t-MCAO, started 18±2h after the induction of stroke, improves NAA levels in the ischemic hemisphere of the treated rats and also prevented deterioration of DI values computed from DWI data, 28 days after t-MCAO. These results were corroborated by behavioral examinations. The fact that treatment was started 18±2h after the t-MCAO shows that electrical SPG-stimulation can potentially extend the therapeutic window for the treatment of ischemic stroke.

                  1351.     Localized ¹H  MRS of Mouse Brain in Vivo Reveals Metabolic Markers Predicting the Development of Ischemic Damage

Hongxia Lei^1,2, Carole Berthet³, Lorenz Hirt³, Rolf Gruetter^1,4

¹EPFL, Lausanne, Vaud, Switzerland; ²UNIL, Lausanne, Vaud, Switzerland; ³CHUV, Lausanne, Vaud, Switzerland; ⁴UNIGE, Geneva, Switzerland

¹H MRS of ischemic mouse brains is feasible at high magnetic field and detects substantial metabolic changes in the neurochemical profile. The aim of the present study was to investigate the effect of different degrees of focal ischemic insults on the neurochemical profiles at an early time-point and to identify markers for reduced cerebral perfusion and for irreversible ischemic damage. The results show that the glutamine increase indicates ischemia and probably reflects ischemia induced glutamate release, while the neuronal markers N-acetylaspartate and glutamate are more likely to indicate an irreversible cerebral lesion.

                  1352.     Molecular MRI of Thrombus in a Rat Ischemic Stroke Model

Ritika Uppal¹, Ilknur Ay¹, Guangping Dai¹, Young Ro Kim¹, Gregory Sorensen¹, Peter Caravan¹

¹Radiology, Massachusetts General Hospital, Charlestown, MA, USA

Ischemic stroke is a leading cause of morbidity and mortality. The identification of the culprit thrombotic lesion, micro-emboli and the source of the embolus are all critical to patient management. We used a fibrin-targeted Gd based contrast agent (EP-2104R) and MRI to characterize a rat thrombo-embolic stroke model. EP-2104R readily identified thrombi in all animals with high contrast to noise, while animals administered GdDTPA showed no thrombus enhancement. These findings correlated with ex vivo tissue measurements of Gd.

                  1353.     Application of a Modified Quantitative BOLD Approach to Monitor Local Blood Oxygen Saturation in Two Glioma Models and a Stroke Model in Rat

Thomas Christen^1,2, Benjamin Lemasson^1,3, Nicolas Pannetier^1,2, Olivier Detante^1,2, Régine Farion^1,2, Emmanuelle Grillon^1,2, Christoph Segebarth^1,2, Chantal Rémy^1,2, Emmanuel L. Barbier^1,2

¹Inserm, U836, Grenoble, F-38043, France; ²Université Joseph Fourier, Grenoble Institut des Neurosciences, UMR-S836, Grenoble, France; ³Oncodesign Biotechnology, Dijon, France

Recently, an in vivo MR approach was introduced to obtain local blood oxygen saturation (lSO2) maps. This study evaluates a modified version of this approach in two rat models: stroke and tumor. Values of lSO2 in the contralateral striatum of rats bearing a brain lesion or in healthy rats are consistent with the literature. The small standard deviation suggests that the proposed lSO2 measurement approach is reproducible. Differences in lSO2 were observed between the two glioma models (C6 and U87-MG) and an increase lSO2 two days after focal brain ischemia, in agreement with a luxury perfusion.

                  1354.     Combined in Vivo MR and Optical Imaging of Stroke Induced Neurogenesis in the Mouse Brain

Tracy Deanne Farr¹, Dirk Wiedermann¹, Sébastien Couillard-Després², Luwig Aigner², Mathias Hoehn¹

¹In-Vivo NMR Laboratory, Max-Planck Institute for Neurological Research, Cologne, Germany; ²Department of Neurology, University of Regensburg, Germany

The formation of new neurons in the adult brain has generated much interest, and could have an impact on recovery from neurodegenerative disease. Neurogenesis is observed using invasive techniques, but the advent of transgenic animals with imaging reporters for cellular or molecular events is a promising alternative. We used mice with a bioluminescent reporter (luciferase) that is produced in response to upregulation of the doublecortin promoter. We are working to establish an in vivo multi-modal optical imaging and MRI protocol to monitor the extent, location, and timecourse of neurogenesis in these mice. Preliminary results indicate this response changes following ischemia.

                  1355.     High Resolution Diffusion Tensor Imaging of Post-Stroke White Matter Integrity in Ex Vivo Rat Brain

Maurits P.A. van Meer^1,2, Willem M. Otte^1,2, Kajo van der Marel¹, Annette van der Toorn¹, J. W. Berkelbach van der Sprenkel², Rick M. Dijkhuizen¹

¹Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands; ²Rudolf Magnus Institute of Neuroscience, University Medical Center Utrecht, Utrecht, Netherlands

DTI may inform on alterations in brain connectivity associated with neuroplasticity. Unbiased whole brain assessment with tract-based spatial statistics analysis (TBSS) was used to determine changes in fractional anisotropy (FA) on high resolution maps of ex vivo post-stroke rat brains. A significant reduction in FA in ipsilesional white matter was detected in 10-weeks post-stroke brains. Ipsi- and contralesional medial corpus callosum showed a significant elevation of FA compared to age-matched controls. These results show that high resolution ex vivo DTI in combination with TBSS analysis allows detailed assessment of degenerative and reorganizational changes in white matter integrity after stroke.

                 1356.     The Diffusion Tensor Reveals Gray Matter Architecture

Sune Norhoj Jespersen¹, Lindsey A. Leigland², Anda Cornea³, Christopher David Kroenke^2,4

¹Center of Functionally Integrative Neuroscience, Aarhus University, Aarhus, Denmark; ²Department of Behavioral Neuroscience, Oregon Health and Science University, Oregon, USA; ³Oregon National Primate Research Center, Oregon Health and Science University, Oregon, USA; ⁴Advanced Imaging Research Center, Oregon Health and Science University, OR, USA

                  1357.     The Effect of Axonal “Beading” on Water Diffusion Properties:  a Monte Carlo Simulation of Axonal Degeneration and Its Effects on DTI Contrasts

Jonathan A.D. Farrell^1,2, Bennett A. Landman³, Jiangyang Zhang², Seth Smith^1,2, Daniel S. Reich^4,5, Peter A. Calabresi⁵, Peter C. van Zijl^1,2

¹F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, USA; ²Neuroscience Section, Division of MR Research, Dept. of Radiology, Johns Hopkins University School of Medicine, Baltimore, MD, USA; ³Dept. of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, USA; ⁴Division of Neuroradiology, Dept. of Radiology, Johns Hopkins University School of Mediciine, Baltimore, MD, USA; ⁵Dept. of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, USA

Axonal degeneration, due to injury or disease, can cause multiple localized dilations (“beading”) of the axonal membrane. The goal of this study was to determine the effect of these morphological changes on diffusion properties measured with DWI. Healthy axons are modeled as cylinders, and degenerating axons are modeled as the union of a cylinder and a sphere of varying radii. Using a Monte Carlo framework, we show that axonal “beading” can cause decreased, non-Gaussian parallel diffusion, and increased perpendicular diffusion. This may aid the interpretation of DWI experiments and advance the development of DTI contrasts specific for axonal injury.

                  1358.     Understanding the Recuded ADC in Stroke Lesions Using Repeated Measurements with Different Diffusion Times

Markus Nilsson¹, Jimmy Lätt², Danielle van Westen², Stig Holtås^2,3, Ronnie Wirestam¹, Freddy Ståhlberg^1,3, Sara Brockstedt²

¹Department of Medical Radiation Physics, Lund University, Lund, Sweden; ²MR Department, Center for Medical Imaging and Physiology, Lund University Hospital, Lund, Sweden; ³Department of Diagnostic Radiology, Lund University, Lund, Sweden

The mechanism behind the reduction of the apparent diffusion coefficient (ADC) in ischaemic stroke is as yet unclear. Effects of water exchange have recently been observed in sub-acute stroke lesions, based on measurements with high b-values and a varied diffusion time. Here we repeated such measurements in two patients, three and ten days after stroke onset. The presence of water exchange was verified. The intracellular signal fraction decreased as the time from the stroke-onset increased and we found indications of different relaxation times in the intra- and extracellular space in the stroke lesions.

                  1359.     Evaluation of the Effect of Exchange on the Diffusion Weighted MR-Signal in Brain White Matter

Els Fieremans^1,2, Yves De Deene^2,3, Jens H. Jensen¹, Joseph A. Helpern¹

¹Department of Radiology, CBI, New York University School of Medicine, New York, NY, USA; ²Department of Electronics and Information Systems, MEDISIP, Ghent University-IBBT-IBiTech, Ghent, Belgium; ³Department of Radiotherapy and Nuclear Medicine, QMRI, Ghent University, Ghent, Belgium

The origin of the anisotropic diffusion weighted (DW) MR-signal observed in brain white matter (WM) is still not completely understood. In this study, Monte Carlo simulations of diffusion are presented in a geometry imitating the white matter. The effect of exchange between the intracellular and extracellular compartment on the DW MR signal has been evaluated. The results show that the diffusion kurtosis is a good probe for the presence of membranes and is sensitive to changes in permeability. Fitting the kurtosis could reveal new insights in the physiology of cells during pathological states.

                  1360.     Renormalization Group Method: Enhancement of Basser-Sen Model of the Brain White Matter

Oleg P. Posnansky¹, N. Jon  Shah^1,2

¹Institute of Neuroscience and Biophysics 3 - Medicine, Research Centre Juelich, Juelich, Germany; ²Faculty of Medicine, Department of Neurology,  RWTH Aachen University,  JARA, Aachen, Germany

We have developed a renormalization group method in order to explore the effects of a large range of geometrical and physical microparameters on the effective apparent diffusion coefficient. The main element of this method comprises the renormalization of structural parameters from the micro to the millimeter scale of the random multi-component white matter of the brain. Our approach enhances the Basser-Sen model by taking the influence of disorder into the consideration and it allows quantitative investigation of the sensitivity of the apparent diffusion coefficient to the variations of the dominant set of micro-parameters.

                  1361.     A Study on the Validity of the Tortuosity Approximation for Extracellular Diffusion Using Monte Carlo Simulations

Hubert Martinus Fonteijn¹, Matt G. Hall¹, Daniel C. Alexander¹

¹Department of Computer Science, Centre for Medical Imaging and Computing, London, UK

Models of extracellular diffusion in biological tissue rely on two assumptions: 1. diffusion is approximately Gaussian for long diffusion times and 2. The relationship between the apparent diffusion coefficient in hindered directions and the free diffusion coefficient is only dependent on the intracellular volume fraction and not on the specific tissue geometry. We have tested these assumptions using Monte Carlo simulations for the diffusion weighted signal using cylinders with gamma-distributed radii. We have found a mono-exponentially decaying signal for only a limited range of b-values. Moreover, the ADC is to some extent related to the distribution of cylinder radii.

                  1362.     Trace Weighting in Double Wave Vector Diffusion Experiments in Vivo

Martin A. Koch^1,2, Jürgen Finsterbusch^1,2

¹Dept. of Systems Neuroscience, University Medical Center Hamburg-Eppendorf, Hamburg, Germany; ²Neuroimage Nord, Hamburg - Kiel - Lübeck, Germany

Double wave vector diffusion weighting may represent a new method for assessing microscopic tissue structure. The difference between parallel and anti-parallel orientations of the gradients in two successive diffusion weighting preparations might be used to estimate the mean size of tissue pores. Calculations for short gradient pulses predict for samples with a non-uniform distribution of pore orientations that a rotation-invariant size estimate can be derived from the sum of measurements along three perpendicular orientations. It is investigated whether this holds true for in vivo experiments on brain tissue using a whole body MR system with finite gradient pulse durations.

                  1363.     Assessment of Tissue Properties and T2 Relaxation on ADC Measurements by Numerical Simulation of Water Diffusion

Kevin D. Harkins¹, Jean-Phillipe Galons², Timothy W. Secomb³, Theodore P. Trouard^1,2

¹Biomedical Engineering, University of Arizona, Tucson, AZ, USA; ²Radiology, University of Arizona, Tucson, AZ, USA; ³Physiology, University of Arizona, Tucson, AZ, USA

The biophysical mechanisms which affect the apparent diffusion coefficient (ADC) have been debated since the initial observation of a drop in ADC following ischemic stroke. A computational model of water diffusion is used to assess the role of intracellular volume fraction (IVF), intracellular diffusion coefficient (Dint), membrane permeability and T2 relaxation on the calculated ADC. Simulations indicate that a 30-50% drop in ADC can be achieved by swelling cells from 80% to 90% IVF when the intracellular T2 was allowed to be lower than extracellular T2. Furthermore, at diffusion times greater than 20 ms, the ADC was virtually independent of Dint.

                  1364.     Validation of Models for the Diffusion Weighted MR Signal in Brain White Matter

Els Fieremans^1,2, Yves De Deene^2,3, Jens H. Jensen¹, Joseph A. Helpern¹

¹Department of Radiology, CBI, New York University School of Medicine, New York, NY, USA; ²Department of Electronics and Information Systems, MEDISIP, Ghent University-IBBT-IBiTech, Ghent, Belgium; ³Department of Radiotherapy and Nuclear Medicine, QMRI, Ghent University, Ghent, Belgium

The diffusion weighted MR-signal attenuation in brain white matter is not mono-exponential. A bi-exponential model has been proposed since this fits the data well. We have modeled the diffusion weighted MR-signal by Monte Carlo simulations in a fiber geometry similar to brain white matter. Although a bi-exponential model fitted the data very well, the fitted diffusion coefficients and fractions did not converge to the simulated values in the intra- and extracellular space. However, fitting the cumulant expansion form terminated after the Nth order term to the data results in accurate fits for the diffusion coefficient and kurtosis.

                  1365.     Evidence for a Vascular Contribution to the Biexponential Signal Decay as a Function of the B-Value in DWI: A Verification of the IVIM-Model

Andreas Lemke¹, Lothar Rudi Schad¹, Bram Stieltjes², Frederik Laun³

¹Chair in Computer Assisted Clinical Medicine, University of Heidelberg, Faculty of Medicine, Mannheim, Germany; ²Department of Radiology, German Cancer Research Center, Heidelberg, Germany; ³Department of Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany

DWI of the abdomen was performed using a global suppression of the blood signal to investigate the vascular contribution to the measured ADC and to validate the IVIM-model. The perfusion fraction f and the diffusion coefficient D were extracted from the measured DW-data of five healthy volunteers with and without blood suppression using a biexponential fit. The perfusion fraction f in the suppressed pancreatic and liver tissue decreased significantly (p=0.008), whereas the diffusion coefficient D did not change with suppression (p>0.5). These results verify a vascular contribution to the DWI-measurement at low b-values and validate the IVIM-theory.

                  1366.     q-Space MR Propagator in Partially-Restricted, Axially-Symmetric and Isotropic Environments

Evren Ozarslan¹, Cheng Guan Koay, Peter J. Basser

¹STBB / LIMB / NICHD, National Institutes of Health, Bethesda, MD, USA

Diffusion may lead to non-symmetric propagators, which can be mapped from the complex-valued MRI signal. Because the true diffusion propagator obeys the reciprocity property, both forward and backward Fourier transforms can be employed, leading to propagators with different meanings. Depending on the geometry, Fourier transform in one direction may provide a more intuitive representation of the geometry than the other. In axially-symmetric and isotropic environments, having one-dimensional data is sufficient to reconstruct higher-dimensional propagators. In these environments, other transforms can be employed, which may make information, otherwise obscured by the one-dimensional Fourier transform, visible.

                  1367.     Analysis of Water Diffusion in White Matter Using a Hydration Layer Model

Elena Olariu¹, Ian Cameron^1,2

¹Physics, Carleton University, Ottawa, Ontario, Canada; ²Diagnostic Imaging , Otawa General Hospital

Diffusion measurements have been made with MRI for many years but an explanation for the observed behavior, in terms of the underlying mechanisms is still illusive. Diffusion decays have frequently been interpreted in terms of a two compartment model with the fast and slow diffusion coefficients associated with extra- and intracellular water, respectively. Unfortunately, the observed signal fractions are not consistent with the true ratio of intra- to extracellular water. Recently, LeBihan has suggested that the two observed components may be associated with free water and hydration water rather than with intra- and extracellular water. It is reasonable to expect that intra- and extracellular hydration water will diffuse more slowly than the rest of the tissue water. The purpose of the research reported here was to investigate this suggestion to see if the predictions of this model are consistent with measured diffusion decay data.

                  1368.     Treatment Response of Non-Monoexponential Diffusion in a Glioma Rodent Model

Benjamin Hoff¹, Denis Le Bihan², Alnawaz Rehemtulla³, Thomas Chenevert¹, Brian Ross¹, Craig Galbán¹

¹Radiology, University of Michigan, Ann Arbor, MI, USA; ²NeuroSpin, CEA, Saclay, France; ³Radiation Oncology, University of Michigan, Ann Arbor, MI

Diffusion MRI at low b-values (~1000 s/mm2) has shown promise as an early surrogate biomarker of treatment response in glioma patients. Recent studies have shown that at higher b-values (>3000 s/mm2) signal attenuation by diffusion deviates from monoexponential behavior in biological tissue. The aim of this study was to test the response of the apparent diffusion coefficient (ADC) calculated from various non-monoexponential models against a conventional two-point low b-value method following chemotherapy in a rodent brain tumor model.

                  1369.     Dependence of Fractional Order Diffusion Model Parameters on Diffusion Time

Xiaohong Joe Zhou^1,2, Qing Gao^1,3, Girish Srinivasan^1,3, Richard L. Magin³

¹Center for MR Research, Univ. of Illinois Medical Center, Chicago, IL, USA; ²Departments of Radiology, Neurosurgery, and Bioengineering, Univ. of Illinois Medical Center, Chicago, IL, USA; ³Dept. of Bioengineering, University of Illinois - Chicago, Chicago, IL, USA

In fractional order diffusion model, anomalous diffusion is described by two new parameters: fractional order spatial derivative â and a spatial variable µ. Although a correlation has been suggested between these parameters and the degree of tissue heterogeneity, the biophysical basis of such correlation has not been established. In this study, we have investigated the effects of diffusion time on these parameters and observed a strong dependence of µ on diffusion time. This result suggests that µ may reflect the degree of diffusion restriction and help establish the interrelation with tissue microstructures.

                  1370.     Diffusion Diffraction Patterns in Different Cells

Davide Imperati^1,2, M. Cross³, Klaus Kruttwig¹, P. Galvosas⁴, Konstantin Ulrich⁴, Andrè Pampel⁵, Jörg Kärger⁴, Mathias Hoehn¹, Harald E. Möller⁵, Marc Tittgemeyer¹

¹Max-Plank Institute for Neurological Research, Cologne, Germany; ²Department of Computer Science, University of Milan, Milan, Italy; ³Interdisciplinary Center for Medical Research, Leipzig, Germany; ⁴Department of Physics, University of Leipzig, Leipzig, Germany; ⁵Max-Plank Institute for Cognition and Brain Science, Leipzig, Germany

Diffusion imaging enables microscopic assessment of tissue microstructures by measuring the displacement of water protons.

                  1371.     Preliminary Experiences with Implementing High Resolution CSF-Suppressed Optic Nerve DTI at 3.0T with and Without Parallel Imaging

Rebecca Sara Samson¹, Mark R. Symms², David L. Thomas³, Madhan Kolappan¹, David H. Miller¹, Claudia A M Wheeler-Kingshott¹

¹Department of Neuroinflammation, UCL Institute of Neurology, London, UK; ²Department of Clinical & Experimental Epilepsy, UCL Institute of Neurology, London, UK; ³Medical Physics & Bioengineering, UCL, London, UK

There are several technical challenges associated with studying the optic nerve (ON) using DTI, in particular its small size, motion, contamination of signal by fat and Cerebrospinal Fluid (CSF), and susceptibility effects pose significant problems. We present our preliminary experiences with the implementation of ON DTI on two different manufacturer’s 3.0T scanners using different data acquisition methods both with and without the use of parallel imaging.

                  1372.     Improvement of DTI Measurement Using the Composite Gradient Systems on a Clinical 3T MRI System: DTI Study of Ex Vivo Dog's Heart

Seong-Eun Kim¹, K Craig Goodrich¹, Sung M. Moon¹, J. Rock Hadley¹, Dennis L. Parker¹

¹UCAIR Department of Radiology, University of Utah, Salt Lake City, UT, USA

Our composite system has the distinct advantage that both of standard and insert gradient systems can be operated simultaneously and/or independently. With simultaneous acquisition, the gradient strength available from either system alone can be increased. Ihe composite gradient system can acquire better DTI measurements with less artifact in human studies than can be obtained with insert or body gradient coils alone. It can also provide high resolution fMRI datasets with better imaging quality compared to data obtained using the standard gradient system.

                  1373.     Accelerating Diffusion Tensor Imaging Using Multi-Reference Image Constrained Reconstruction

Lindsey Jean Healy¹, Osama Abdullah¹, Edward W. Hsu¹

¹Bioengineering, University of Utah, Salt Lake City, UT, USA

MR diffusion tensor imaging (DTI) has suffered from long scan times, low SNR and resolution. This study examines the accuracy and efficiency of selected schemes to accelerate DTI via reduced encoding and multi-reference constrained reconstruction. Results indicate that generalized-series constrained reconstruction combined with direction-dependent, model-estimated images as references can be used to further improve DTI acquisition efficiency than that achieved previously using a single reference image. The findings support the validity of applying reduced sampling and constrained reconstruction to accelerate DTI, and are particularly promising for 3D DTI, high angular-resolution diffusion imaging, or other experiments that require extremely large datasets.

                  1374.     High b-Value Acquisition Using CURVE-Ball DTI

Sharon Peled¹, Stephen Whalen², Alexandra Golby²

¹Radiology, Brigham and Women's Hospital, Boston, MA, USA; ²Neurosurgery, Brigham and Women's Hospital

A new strategy for obtaining high SNR high b-value DTI information in brain is presented. The basis for the approach is the independence of DTI eigenvector directions from the b-value at which the acquisition takes place. This allows determination of the eigenvectors from relatively low b-value DTI. Thus with the help of an appropriate diffusion model, diffusion curves for each eigenvector can be generated using only sparse sampling of high b-value data. The method will enable better diffusion-based tissue characterization in clinical and research settings where scan time is a limiting factor.

                  1375.     Apparent Diffusion Coefficient Measurement of in Vivo Atherosclerotic Plaque Obtained from Six Human Subjects Using 2D Ss IMIV DWEPI Technique on 3T System

Seong-Eun Kim¹, Eun-Kee Jeong¹, J. Rock Hadley¹, John A. Roberts¹, Gernald A. Trieman^2,3, Laura C. Bell¹, Dennis L. Parker¹

¹UCAIR Department of Radiology, University of Utah, Salt Lake City, UT, USA; ²Surgical Service, VA Salt Lake City Health Care System; ³Department of Surgery School of Medicine, University of Utah

In this work we present the in vivo ADC measurement of in vivo atherosclerotic plaque obtained from six human subjects. The results obtained indicate that ADC map may be of substantial value as a new contrast for carotid plaque imaging. Although our ADC values obtained using the 2D ss IMIV DWEPI technique fall within the range of previously reported ADC value in an ex-vivo study, there is no previously known ADC value of each plaque component from an in-vivo study. The technique demonstrated here can now be used to further investigate the ADC in all types of plaque components.

                  1376.     Parallel Line Scan Diffusion Imaging with 2D Acceleration

Renxin Chu¹, Bruno Madore¹, Lawrence P. Panych¹, Mohammed H. Aljallad¹, Stephan E. Maier¹

¹Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA

Line scan diffusion imaging (LSDI) is a one-dimensional Fourier encoding techniques that typically does not involve phase encoding. The absence of phase encoding provides considerable robustness against motion and immunity from artifacts caused by field inhomogeneities and susceptibility. We propose a novel parallel line scan diffusion imaging with 2D acceleration technique by modulating the 90° and 180° slice selection pulses with a cosine waveform to yield double column excitation in 2D simultaneously. Four-fold acceleration can be achieved, at no cost in SNR. Human brain imaging was carried out to test the technique. The proposed accelerated technique preserves the significant advantages of line scan diffusion imaging, more specifically, immunity from susceptibility-induced signal loses and geometric image distortions.

                  1377.     Measuring and Correcting Errors That Occur in Diffusion Weighted Images Due to Non-Ideal Gradient Linearity

Zoltan Nagy¹, Daniel C. Alexander², Nikolaus Weiskopf¹

¹Wellcome Trust Centre for Neuroimaging, University College London, London, UK; ²Center for Medical Image Computing, University College London, London, UK

Because the diffusion weighting depends on the gradient amplitude to the second power, any deviations from the linearity in the gradient systems are amplified in ADC images. However, if this deviation in the gradient amplitude is known for each voxel the diffusion weighting b-value can be corrected, giving the accurate ADC measurement in every voxel. We provided a simple method of estimating the errors due to each of the diffusion encoding gradients and a simple formula for voxelwise correction of the ADC images.

                  1378.     Feasibility of In-Vivo Diffusion Tensor Echo Planar Imaging and Fiber Tracking at 14.1T

Nicolas Kunz^1,2, Yohan van de Looij^1,2, Petra S. Hüppi², Stéphane V. Sizonenko², Rolf Gruetter^1,3

¹Laboratory for Functional and Metabolic Imaging, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland; ²Division of Child Growth & Development, Department of Pediatrics, University of Geneva, Geneva, Switzerland; ³Department of Radiology, University of Geneva and Lausanne, Geneva and Lausanne, Switzerland

Despite the high interest of combination of DTI and MRS at ultra-high magnetic field, none such multimodal in vivo studies in the rodent brain have been published. This combination is very challenging due to different requirements of the two modalities. High resolution MRS requires the use of a transceive surface coil. The aim of this study was to implement a DTI-EPI sequence with whole brain coverage at 14.1T, while using a surface coil as both transmitter and receiver. We demonstrate the feasibility of in vivo DTI-EPI at 14.1T using a transceive surface coil with whole brain coverage.

                  1379.     Comparison of Reduced-FOV Single-Shot EPI Methods for DWI: ZOOM-EPI Vs. 2D Echo-Planar RF Excitation

Emine Ulku Saritas¹, Ken-Pin Hwang², Eric T. Han³, Jin Hyung Lee¹, Dwight George Nishimura¹, Ajit Shankaranarayanan³

¹Department of Electrical Engineering, Stanford University, Stanford, CA, USA; ²Applied Science Laboratory, GE Healthcare, Houston, TX, USA; ³Global Applied Science Laboratory, GE Healthcare, Menlo Park, CA, USA

Single-shot EPI (ss-EPI) is still the most widely used DWI sequence, due to its robustness against motion-induced phase perturbations. However, it is challenging to produce high-resolution diffusion images using ss-EPI. Several reduced-FOV methods have recently been proposed to overcome this challenge. In this work, we compare two of these methods: Reduced-FOV with 2D echo-planar RF (2D-EPRF) excitation and ZOOM-EPI. To achieve a thorough comparison, we present in vivo sagittal and axial DWI of the spinal cord using both techniques.

                  1380.     Double-Spin-Echo Diffusion Weighting with a Modified Eddy-Current Adjustment

Jürgen Finsterbusch^1,2

¹Dept. of Systems Neuroscience, University Medical Center Hamburg-Eppendorf, Hamburg, Germany; ²Neurimage Nord, Hamburg-Kiel-Lübeck, Germany

Echo-planar imaging suffers from geometric distortions in the presence of eddy currents which in particular are prominent after applying diffusion-weighting gradient pulses. To reduce these eddy currents, a double-spin-echo preparation is commonly used where the four pulse durations are adjusted to null eddy currents of a given time constant. However, eddy currents with different time constants are usually present yielding residual geometric distortions. It is shown that these residual distortions can be reduced when adjusting the two gradient pairs to different time constants. Although none of the time constants is compensated completely, the overall eddy-current performance can be improved.

                  1381.     K-Space and Image Space Combination for Motion-Induced Phase Error Correction in 3D Diffusion-Weighted Imaging

Anh Tu Van¹, Dimitrios C. Karampinos^2,3, Bradley P. Sutton^1,4

¹Electrical and Computer Engineering, University of Illinois, Urbana, IL, USA; ²Mechanical Science and Engineering, University of Illinois, Urbana, IL, USA; ³Beckman Institute, University of Illinois, Urbana, IL, USA; ⁴Bioengineering, University of Illinois, Urbana, IL, USA

3D diffusion-weighted imaging (DWI) is highly desirable when high-resolution isotropic voxels are needed in diffusion tensor imaging. However, 3D DWI is prone to motion-induced phase errors, much more than the 2D DWI case. In this work, we extend a previously developed method for motion-induced phase error correction to 3D DWI data. Based on a simple 3D acquisition strategy and rigid-body motion model for the motion-induced phase errors, the new method is time efficient. Both simulation and in vivo experiments are performed to demonstrate the robustness and effectiveness of the proposed method.

                  1382.     Hadamard Slice Encoding for Reduced-FOV Single-Shot Diffusion-Weighted EPI

Emine Ulku Saritas¹, Ajit Shankaranarayanan², Dwight George Nishimura¹

¹Department of Electrical Engineering, Stanford University, Stanford, CA, USA; ²Global Applied Science Laboratory, GE Healthcare, Menlo Park, CA, USA

A reduced-FOV single-shot EPI method that uses a 90^o 2D echo-planar RF excitation has recently been proposed to achieve high-resolution DWI. This method is compatible with contiguous multi-slice imaging without the need for slice skip. However, there is a limit on the number of slices that can be imaged in a simultaneously, determined by the number of slices that can fit between the two adjacent sidelobes of the periodic 2D excitation profile. In this work, we present two different Hadamard slice encoding schemes to double the number of slices for the reduced-FOV method. Specifically, the refocusing 180^o RF pulse used to achieve Hadamard slice encoding can be applied either on the two adjacent sidelobes, or on the main lobe of the 2D excitation profile.

                1383.     Pearson Set of Distributions as Improved Signal Model for Diffusion Kurtosis Imaging

Dirk H. J. Poot¹, Arjan J. den Dekker², Jan Sijbers¹

¹Visionlab, University of Antwerp, Antwerp, Belgium; ²Delft Center for Systems and Control, TUDelft, Delft, Netherlands

This work explains a new model which includes the kurtosis of the diffusion process in the model of the recorded diffusion weighted images. This new model is based on the Pearson set of statistical distributions. Compared to the traditional Taylor approximation based model of the diffusion weighted images, this model provides more realistic and accurate predictions of the magnitude of the diffusion weighted images, especially for large b-values. To be able to estimate the kurtosis, these large b-values are needed. Therefore, this improved model is relevant for the estimation of kurtosis measures from diffusion weighted images.

                  1384.     Importance of Multiscale Analysis in HARDI Studies

Irina Kezele¹, Cyril Poupon¹, Maxime Descoteaux¹, Fabrice Poupon¹, Jean-François Mangin¹

¹NeuroSpin, CEA, Saclay, France

High angular resolution distribution diffusion imaging (HARDI) implicitly captures information about the structure in which the diffusion process takes place. HARDI allows examination of relatively wide range of diffusion signal angular frequencies that, due to the complexity of both diffusion process and its milieu, may spread over multiple bands. In consequence, we opt for multiscale analysis, probing all frequencies, but also favouring those frequencies that are more in concordance with our specific aims, which are to deduce and sharpen fibre distributions. Inherent HARDI signal sphericity motivated us to take on the concepts of multiscale spherical wavelet analysis. We show the importance of multiscale signal analysis, and how different angular frequency bands may capture complementary information on underlying fibre distribution.

                  1385.     Groupwise Non-Rigid Registration of 4th-Order Diffusion Tensor Fields and Atlas Construction

Angelos Barmpoutis¹, Baba C. Vemuri¹, Dena Howland², John R. Forder³

¹CISE, University of Florida, Gainesville, FL, USA; ²Neuroscience, University of Florida, Gainesville, FL, USA; ³Radiology, University of Florida, Gainesville, FL, USA

In this work we present a method for simultaneous groupwise non-rigid registration of 4th-order tensor fields and atlas construction. To achieve the task of registration, we first define a novel distance measure on 4th order tensors using the Riemannian metric of positive real numbers. This metric is employed in an unbiased cost function, that is being minimized in order to estimate the unknown deformation fields and at the same time construct the unknown 4th-order tensor field atlas. We demonstrate the method using DW-MRI datasets from three rat spinal cords.

                  1386.     A Comparison of Two Models of Anomalous DWI Based on a Known Distribution of Water Diffusion Rates

CHU-YU LEE¹, Kevin M. Bennett², Lina J. Karam¹, Joseph P. Debbins³

¹Department of Electrical Engineering, Arizona State University, Tempe, AZ, USA; ²Harrington Department of Bioengineering, Arizona State University, Tempe, AZ, USA; ³Keller Center for Imaging Innovation, Barrow Neurological Institute, Phoenix, AZ, USA

Sretched exponential (£\DWI) and second-order cumulant (DKI) models were developed to describe the non-monoexponential signal attenuation of a DWI experiment. Both £\ and Kapp are thought to reflect heterogeneity in water diffusion rates, but their relationship to the underlying biophysics is still unclear. In this work, we simulated a simplified physical system of either one or two water compartments with a known distribution of water diffusion rates, and studied how these two models behaved. Our results showed that £\ is directly related to var[D] in both the one- and two-compartment models. Kapp is sensitive to both to E[D] and var[D]. Besides, £\DWI may be preferred when high b-values can be used, but DKI may be preferred at low b-values. However, because DKI is limited to low b-value ranges, it may be insensitive to changes in slow diffusion. These two models are thus similar, but have separate relationships to the intravoxel distribution of water diffusion rates.

                  1387.     Non-Rigid Registration of Diffusion Weighted Images Using Fibre Orientation Distributions

David Raffelt^1,2, J-Donald Tournier^3,4, Jurgen Fripp⁵, Natasha Lepore⁶, Stuart Crozier², Alan Connelly^3,4, Olivier Salvado¹

¹The Australian E-Health Research Centre, CSIRO, Brisbane, QLD, Australia; ²Department of Biomedical Engineering, University of Queensland, Brisbane, QLD, Australia; ³Brain Research Institute, Florey Neuroscience Institutes (Austin), Melbourne, VIC, Australia; ⁴Department of Medicine, University of Melbourne, Melbourne, VIC, Australia; ⁵The Australian E-Health Research Centre, CSIRO,, Brisbane, QLD, Australia; ⁶Laboratory of Neuro Imaging, David Geffen School of  Medicine UCLA, Los Angeles, CA, USA

Fibre Orientation Distributions (FODs) obtained from diffusion weighted imaging (DWI) provide a non-invasive method to investigate white matter structure and connectivity. In order to compare white matter between individuals, spatial normalisation is required. We propose a free form deformation registration method using a novel similarity measure that optimises directly on FODs. Our technique compared favourably with existing T1 weighted and fractional anisotropy based methods: average images were sharper indicative of more accurate spatial alignment. Unlike existing scalar or diffusion tensor based techniques, this method exploits information provided by FODs in voxels with crossing fibres, independently of how FOD are computed.

                  1388.     Spatial Transformations of Fiber Orientation Fields

Rafael Alonso Clarke^1,2, Giovanna Rizzo³, Daniela Perani⁴, Giuseppe Scotti², Ferruccio Fazio^1,3, Paola Scifo^1,2

¹Nuclear Medicine, San Raffaele Scientific Institute, Milan, -, Italy; ²CERMAC, San Raffaele Scientific Institute, Milan, -, Italy; ³IBFM, CNR, Milan, -, Italy; ⁴Università Vita-Salute San Raffaele, Milan, -, Italy

To perform group-level analyses and compare subjects, due to differences in brain shape and size, geometrical transformations must be applied to images to overlap regions.For DTI, the directional information can be considered in transformations using the Preserve Principal Directions method.In this work we present a novel method that we call Preservation of Principal Branches, for the transformation of Fiber Orientation Distribution objects (FODs) that takes into account their specific shapes.

                  1389.     A Polynomial Based Approach to Extract Fiber Directions from the ODF and Its Experimental Validation

Aurobrata Ghosh¹, Elias Tsigaridas², Maxime Descoteaux³, Rachid Deriche⁴

¹Project Odyssée, INRIA Sophia Antipolis Méditerranée, Sophia Antipolis, Alpes Maritimes, France; ²Project GALAAD, INRIA Sophia Antipolis Méditerranée, France; ³NMR Lab, Neurospin / CEA, Saclay, France; ⁴Project Odyssée, INRIA Sophia Antipolis Méditerranée, France

This paper presents a polynomial based approach for extracting the maximal directions of a spherical function, for example the ODF. It rewrites the ODF in the homogeneous polynomial (HP) basis constrained to the sphere and solves a constrained optimization problem algebraically. This guarantees that all the maxima are computed at once and also provides a measure for the quality of the maxima estimation. Since it works with a continuous polynomial function, this approach is not dependent on a discrete mesh for the mesh-resolution and mesh-orientation. The approach is tested on synthetic, phantom and real datasets and compared to a discrete mesh search approach. It is shown how this HP method naturally overcomes the inherent limitations of the discrete search method.

                  1390.     Estimation of Cell Size Using the Composite Hindered and Restricted Model of Diffusion

Yaniv Sagi¹, Peter J. Basser², Yaniv Assaf¹

¹Department of Neurobiology, Tel Aviv University, Tel Aviv, Israel; ²Eunice Kennedy Shriver National Institute of Child Health and Human Development, The National Institutes of Health, Bethesda, MD, USA

In this work we used diffusion imaging to estimate the average size of cells in a culture. Two cell cultures differing in cell size were scanned. The signal decay appears to be multi-exponential, indicating multi-compartmetation or restricted diffusion. The signal was fitted to a model of diffusion in two compartments: a hindered, extra-cellular compartment and a restricted, intra-cellular compartment. This enabled us to estimate the mean size of cells in each culture and the volume fractions of intra- vs. extra-cellular matrices. The results are in agreement with known sizes of these types of cells.

                  1391.     Diffusion Propagator Imaging (DPI): An Alternative to Diffusion Spectrum Imaging (DSI)

Maxime Descoteaux¹, Kuan-Hung Cho², Yi-Ping Chao³, Chun-Hung Yeh³, Jean-François Mangin¹, Ching-Po Lin³, Cyril Poupon¹

¹NeuroSpin, IFR 49, CEA Saclay, Gif-sur-Yvette, France; ²National Taiwan University, Taiwan; ³National Yang-Ming University, Taiwan

                  1404.     Outlier Detection for Diffusion Tensor Imaging by Testing for ADC Consistency

Hangyi Jiang^1,2, Min-chung Chou^1,2, Peter C.M. van Zijl^1,2, Susumu Mori^1,2

¹Johns Hopkins University, Baltimore, MD, USA; ²Kennedy Krieger Institute, Baltimore, MD, USA

                  1436.     Stochastic Fibre Tracking: An Average Curves Approach

Nagulan Ratnarajah¹, Andy Simmons², Ali Hojjat³

¹Department of BioSciences, University of Kent, Canterbury, Kent, UK; ²Centre for Neuroimaging Sciences, Kings College London, UK; ³Department of BioSciences, University of Kent, UK

To resolve orientational uncertainties in diffusion tensor imaging, probabilistic fiber tracking has received considerable interest. Current approaches model the uncertainty at each voxel with a probability density function (PDF) for the fiber orientations, then propagate a streamline in randomly sampled directions, and the most probable path is estimated using the connectivity map. We consider the random path as a set of curves, and find the most probable path estimated directly from the generated curves using average curves. A simple stochastic model is presented here and two implementations evaluated using phantom and in vivo diffusion MRI data

                  1437.     Diffusion Simulation Tractography for High Angular Resolution Diffusion Imaging

Ning Kang¹, Gregory T. Balls¹, Lawrence R. Frank^1,2

¹Center for Scientific Computation in Imaging, University of California San Diego, La Jolla, CA, USA; ²Radiology Department, VASDHS, San Diego, CA, USA

Regions of complex fiber architecture in the presence of multiple fiber orientations within a single voxel are common in the brain and pose a significant problem for standard DTI (Diffusion Tensor Imaging) based fiber tracking methods, therefore limit the utility of HARDI (High Angular Resolution Diffusion Imaging) acquisition techniques. Here we propose an extension of our previously demonstrated diffusion simulation tractography method to HARDI technique that has potentials to overcome these limitations and thus provide more information about connectivity in the brain.

                  1438.     Probabilistic Fiber Tracking Using the Residual Bootstrap with Constrained Spherical Deconvolution MRI

Ben Jeurissen¹, Alexander Leemans², Jacques-Donald Tournier^3,4, Jan Sijbers¹

¹Visionlab, Dept. of Physics, University of Antwerp, Antwerp, Belgium; ²CUBRIC, School of Psychology, Cardiff University, Cardiff, Wales, UK; ³Brain Research Institute, Florey Neuroscience Institutes (Austin), Melbourne, Victoria, Australia; ⁴Dept. of Medicine, University of Melbourne, Melbourne, Victoria, Australia

We present a new probabilistic tractography algorithm based on constrained spherical deconvolution (CSD) of diffusion weighted (DW) MRI and the residual bootstrap. Using simulations we show that the residual bootstrap is an accurate method to characterize CSD fiber trajectory uncertainty. As opposed to classic bootstrapping, the residual bootstrap only requires a single DW acquisition, making it clinically feasible. We compare our algorithm to state-of-the-art probabilistic diffusion tensor imaging (DTI) tractography, using both simulated and real DW data. Our algorithm is shown to be much less prone to fiber dispersion than probabilistic DTI tractography in regions of multiple fiber orientations.

                  1439.     Free-Spin Tracking: A Novel Global Tractography Algorithm

Pierre Fillard¹, Cyril Poupon¹, Jean-François Mangin¹

¹LNAO, CEA/DSV/I2BM/Neurospin, Gif/Yvette, France

We propose a novel tractography algorithm able to handle various fiber configurations like crossings. Fibers are modeled as chains of unit elements called spins. Spins are allowed to move, merge with other spins, and duplicate to form longer pieces of fibers. The entire white matter is tracked at once, which allows pieces of fibers coming from the entire volume to help find the optimal neuronal pathway in crossing regions. Experiments on two realistic MR phantoms show that such approach is successful in reconstructing fiber crossings and kissings, even using a simple diffusion model like the tensor.

                  1440.     Model-Based Streamline Rejection for Probabilistic Tractography

Jonathan D. Clayden¹, Chris A. Clark¹

¹Institute of Child Health, University College London, London, England, UK

This work describes a method for rejecting false positive pathways in probabilistic tractography based on a model of tract shape. Unlike with region-of-interest methods, the rejection criterion is probabilistic and based on the topology of the tract in each individual. In contrast to thresholding approaches, the method is sensitive to the meaning of the data and has no user-defined parameters. The common observation of declining visitation count with distance from a seed point is also alleviated.

                  1441.     Preliminary Results on the Use of STAPLE for Evaluating DT-MRI Tractography in the Absence of Ground Truth

Sonia Pujol¹, Carl-Fredrik Westin², Ross Whitaker³, Guido Gerig³, Tom Fletcher³, Vincent Magnotta⁴, Sylvain Bouix⁵, Ron Kikinis¹, William M. Wells III¹, Randy Gollub⁶

¹Surgical Planning Laboratory, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA; ²Laboratory of Mathematics in Imaging, Brigham and Women's Hospital, Harvard Medical School, Boston, MA; ³Scientific Computing and Imaging Institute, University of Utah, Salt Lake City, UT; ⁴University of Iowa, Iowa City, IA; ⁵Psychiatry Neuroimaging Laboratory, Boston, MA; ⁶Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Boston, MA

We describe preliminary results obtained from a framework for evaluating DT-MRI tractography algorithms that uses STAPLE (Simultaneous Truth and Performance Level Estimation) to estimate the performance of the methods in the absence of ground truth. In tests on a mathematical phantom we show that STAPLE is able to characterize fiber tracking performance by comparing its findings to true performance findings. We apply the framework to four methods operating on four white matter fasciuli in real data, and describe the results of this new approach for validating tractography.

                  1442.     Whole-Brain Track-Density Mapping as a Tool for Fiber Tractography

Fernando Calamante^1,2, Jacques-Donald Tournier^1,2, Heath Pardoe^1,2, Alan Connelly^1,2

¹Brain Research Institute, Florey Neuroscience Institutes (Austin), Melbourne, Victoria, Australia; ²Department of Medicine, University of Melbourne, Melbourne, Victoria, Australia

This study describes the use of whole-brain track-density mapping as a complementary tool for tractography. In particular, it is demonstrated to aid in definition of seed and target regions for tractography (making that important step more robust), and to facilitate normalization of fiber tracks for inter-subject comparisons. The maps are shown to have very good anatomical contrast, high spatial resolution, high SNR and, importantly, they are exactly in the same space (including distortions) as the diffusion data. Whole-brain track-density maps should play an important role in clinical and research studies.

                  1443.     A Global Approach to Diffusion Tensor Neighborhood Tractography

Paul A. Armitage¹, Susana Munoz Maniega¹, Mark E. Bastin²

¹Clinical Neurosciences, University of Edinburgh, Edinburgh, City of Edinburgh, UK; ²Medical & Radiological Sciences (Medical Physics), University of Edinburgh, Edinburgh, City of Edinburgh, UK

Neighborhood tractography has been shown to be beneficial for automating the extraction of white matter pathways in the brain. However, present implementations are generally specific to local tractography algorithms, such as those based on streamlining. Therefore, a neighborhood tractography framework is developed suitable for use with global tractography algorithms. When applied in conjunction with fast marching tractography, the method improved the automatic extraction of connectivity maps for white matter pathways of interest when compared to transposing seed points by registration alone.

                  1444.     Spatial Random Effects Modelling of Crossing Fibre Voxels in Diffusion MRI

Martin David King¹, Chris Alan Clark¹, David Gadian¹

¹UCL Institute of Child Health, University College London, London, UK

A spatial random effects model has been used in the analysis of multiple-directions diffusion-weighted MR data, focussing on the crossing-fibre problem that arises in tractography. The analysis was performed with the Markov chain Monte Carlo Gibbs sampler algorithm, using crossing fibre low b-value (1000 s mm-1) 20 directions diffusion data acquired from the pons. The results show that spatial random effects modelling, based on a conditional autoregressive prior, provides well resolved components compared with those obtained with an equivalent independent voxel-by-voxel treatment. We conclude that the spatial random effects modelling approach provides a useful extension to current tractography methods.

                  1445.     HYFF-HYbrid Tractography with Fiber Assignment by Continuous Tracking and Fast Marching

Hao Huang^1,2, Xin Fan¹

¹Advanced Imaging Research Center, UT Southwestern Medical Center, Dallas, TX, USA; ²Department of Radiology, UT Southwestern Medical Center, Dallas, TX, USA

Tractography based on diffusion tensor imaging (DTI) provides an efficient and noninvasive means to reveal the morphology of white matter tracts. Conventional streamline method such as FACT is known to have limitation of tracing only single lines. Fast marching tractography (FMT) allows fiber crossing and branching based on DTI, but is bound to discretization errors. The proposed HYFF (HYbrid tractography with Fiber assignment by continuous tracking and Fast marching) is a streamline method which ensures correct directions of tracing by forcing the traced lines to go downstream of the time field generated from FMT.

                  1446.     Measuring Error of Diffusion MRI-Based Brain Connectivity Matrices with Residual Bootstrap

Christopher T. Nguyen^1,2, Roland G. Henry^2,3, SungWon Chung^2,3

¹Bioengineering, University of California Berkeley, Berkeley, CA, USA; ²Center for Molecular and Functional Imaging, Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, USA; ³Graduate Group in Bioengineering, University of California San Francisco and Berkeley, San Francisco, CA, USA

Recently, noninvasive techniques using diffusion MRI were used to construct in-vivo brain connectivity matrices and networks. While exciting, the potential variability of these connectivity matrices is not known and will depend on several factors including data acquisition and fiber tracking algorithms. Using residual bootstrap, we propose a method to measure the errors in whole brain connectivity matrices and present results based on a deterministic fiber-tracking algorithm. The resulting matrix demonstrated high variability in many of the pairs of ROIs especially in known crossing fiber regions.

                  1447.     Improved Probabilistic Tractography Using Atlas-Based Fiber Tracking

Qing Xu¹, Adam W. Anderson¹, John C. Gore¹, Zhaohua Ding¹

¹Vanderbilt University Institute of Imaging Science (VUIIS), Vanderbilt University, Nashville, TN, USA

A probabilistic fiber tracking algorithm generates a set of fibers that reflect the distribution of underlying neuronal pathways by processing the diffusion tensor images. As imaging artifacts such as random noise and partial volume averaging usually render reconstructed fibers unreliable, typically certain prior knowledge is used to regularize the fiber tracking process. In this contribution, we propose a novel atlas based probabilistic fiber tracking algorithm that incorporates prior knowledge from a white matter fiber atlas, thereby eliminating the need for the commonly used heuristic priors.Preliminary experiments demonstrate that the atlas-guided method improves probabilistic tractography over methods with heuristic priors.

                  1448.     Automated Registration, Segmentation and Labeling of White Matter Fiber Tracts

Qing Xu¹, Adam W. Anderson¹, John C. Gore¹, Zhaohua Ding¹

¹Vanderbilt University Institute of Imaging Science (VUIIS), Vanderbilt University, Nashville, TN, USA

Brain white Matter (WM) fibers are widely reconstructed by using magnetic resonance diffusion tensor imaging (DTI). A fiber-to-bundle registration algorithm is proposed to coregister a whole-brain target fiber set with an already reconstructed reference bundle set. Using the resulting transformation, the fibers from different target datasets can all be warped into the reference space for comparison and group analysis. Moreover, their bundle type can be automatically labeled. Experiments with eight human brain DTIs have shown significant similarity of the reference with the post-registered target bundles, and also high consistency of the resulting bundles with a manually segmented ground truth.

                  1449.     Gender Differences in White Matter Microstructure in the Adult Brain Revealed by Tract Based Spatial Statistics.

Emer Judith Hughes¹, David J. Sharp², Derek L.G Hill³, Alle Meije Wink⁴, Joseph V. Hajnal⁴, Serena J. Counsell⁵

¹Robert Steiner MRI Unit, Hammersmith Hospital, Imperial College, London, England, UK; ²Cognitive Neuroimaging Group, MRC Clinical sciences Centre, Imperial college, London, England, UK; ³The London Bioscience Innovation Centre, IXICO ltd, London, England; ⁴Hammersmith Hospital, Imperial College, Robert Steiner MRI Unit, London, England, UK; ⁵Robert Steiner MRI Unit, Hammersmith Hospital, Imperial college, London, England, UK

Diffusion tensor imaging studies (DTI) have found evidence for sexual dimorphism in a number of white matter tracts, with males having higher fractional anisotropy (FA) than females. The aim of this study was to assess whole brain white matter, in a large study group, in order to assess the extent of these microstructural differences using Tract Based Spatial Statistics (TBSS). Our results demonstrated extensive regions in the brain where the white matter microstructure differs between males and females, including a number of regions that have not been previously reported.

                  1450.     Separate Assessment of Diffusion Properties of NAA and NAAG at 7T

Hermien E. Kan¹, Matthias J. P. van Osch¹, Maarten J. Versluis¹, Aranee Techawiboonwong², Mark A. van Buchem¹, Andrew J. Webb¹, Itamar Ronen²

¹Leiden University Medical Center, Leiden, Netherlands; ²Department of Anatomy and Neurobiology, Boston University School of Medicine, Boston, MA, USA

In diffusion weighted spectroscopy (DWS), the behaviour of intra cellular metabolites can potentially give information on compartmentation, in contrast to water for which measurements are not specific for any compartment. In this work, we measure for the first time in humans the different diffusive properties of N-Acetyl aspartate (NAA) and N-Acetylaspartylglutamate (NAAG) by applying DWS at a field strength of 7T, where there is sufficient spectral separation to perform this measurement

                  1451.     Separation of Fiber Tracts Within the Human Cingulum Bundle Using Single-Shot STEAM DTI with Partial Fourier Encoding and Parallel Imaging

Alexander Karaus¹, Sabine Hofer¹, Jens Frahm¹

¹Biomedizinische NMR Forschungs GmbH, Goettingen, Germany

The purpose of this work was to present the cinglulum bundle located above the corpus callosum. It consists of a complex white matter fiber tract of the human brain that comprises long association fibers, commissural fibers, and various U-fibers. The fiber tractography was achieved by diffusion tensor imaging using a single-shot STEAM-sequence with 24 gradient directions at 1.8 mm isotropic resolution. In order to map the full cingulum bundle 41 oblique sections in AC-PC orientation were acquired without gaps in an interleaved order.

                  1452.     How to Smooth Diffusion Tensor Images in a Voxel Based Analysis?

Wim Van Hecke¹, Alexander Leemans², Steve De Backer¹, Paul M. Parizel³, Jan Sijbers¹

¹University Antwerp, Antwerp, Belgium; ²CUBRIC, University of Cardiff, Cardiff, Wales, UK; ³Radiology, Antwerp University Hospital, Antwerp, Belgium

Many DTI studies are starting to use voxel based analysis (VBA) to evaluate differences in the diffusion properties between healthy diseased subjects. In this work, simulated DTI data sets with a predefined pathology are used to evaluate the sensitivity and specificity of the pathology detection comparing isotropic and anisotropic smoothing kernels with different full width at half maximum. We demonstrate that the use of anisotropic kernels can increase the sensitivity and the specificity of detecting a pathology in a VBA. We therefore suggest to apply an anisotropic smoothing method in DTI group studies to increase SNR while preserving WM boundaries.

                  1453.     Diffusion Tensor Invariants and Principal Eigenvector Coherence Changes with Field Strength at Various b-Value Ranges

Ai Wern Chung¹, Martin D. King¹, David L. Thomas², Roger J. Ordidge², Chris A. Clark¹

¹Radiology & Physics Unit, UCL, Institute of Child Health, London, UK; ²Department of Medical Physics, UCL, Wellcome Trust High Field MR Research Laboratory, London, UK

Our aim is to assess the effect of magnetic field strength on diffusion tensor invariants, including principal eigenvector coherence, over b-values 0 to 3000 s mm^-2 in healthy subjects. We found a significant increase in FA at 3.0 T versus 1.5 T for all b-values tested in white matter, with overall FA decreasing at high b. Field strength was found to be a significant main effect on the accompanying principal eigenvector coherence, also exhibiting a decreasing trend with increasing b. In summary, the improvement of SNR with field strength saw significant increase in white matter FA along with coherence.

                  1454.     Segmentation and Characterisation of White Matter Tracts in Late Childhood and Adolescence

Jonathan D. Clayden¹, Catherine J. Riney¹, Janine Cooper¹, Monica Muñoz¹, Chris A. Clark¹

¹Institute of Child Health, University College London, London, England, UK

This work describes the application of the recently-developed probabilistic neighbourhood tractography (PNT) method to data acquired from subjects in late childhood or adolescence. Using this method, we segmented a number of white matter tracts in each subject's data, and investigated the effects of age and gender on diffusion parameters. We found clear differences between the tracts, and we demonstrate some evidence for a lateralisation effect which is at least partly modulated by gender.

                  1455.     Micro-Architectural Features of the in Vivo Human Optic Chiasm

Joelle E. Sarlls¹, Carlo Pierpaoli¹

¹NICHD, National Institutes of Health, Bethesda, MD, USA

Diffusion tensor images were acquired at sub-millimeter resolution, in-vivo, in the oblique plane of the optic nerves/chiasm/tracts. Acquiring data at sub-millimeter resolution dramatically reduces partial volume effects, allowing quantitative measures of the optic chiasm without CSF contamination and increased fiber coherence. In addition to the commonly calculated parameters of diffusion, measures of the diffusion ellipsoid’s shape were also calculated. We observe that there are not only architectural differences in the crossing and uncrossed fibers of the medial and latteral optic chiasm, but that the trajectory of crossing fibers may depend on their dorsal/ventral location in the chiasm as well.

                  1456.     Stability of Diffusion Direction Based Thalamus Segmentation

Sarah C. Mang¹, Uwe Klose¹, Susanne Reiterer^1,2, Wolfgang Grodd¹

¹Section Exp. MRI of CNS, Diagnostic and Interventional Neuroradiology, Tübingen, Germany; ²Hertie Institute for Clinical Brain Research, General Neurology, University of Tübingen, Tübingen, Germany

A simple diffusion direction based segmentation method was used to distinguish thalamic sub-structures on 53 healthy volunteers. This segmentation method classifies voxels according to the orientation of their principal diffusion direction. The results of this simple segmentation method were stable in the evaluated subject population. Our segmented clusters did in addition show a correspondence to the clusters segmented with a more complicated connectivity based segmentation approach.

                  1457.     Detection of Motor Thalamus by Probabilistic Diffusion Density : Verification by Motor BOLD-Based FMRI

Tzu-chen Yeh¹, Zong-Kai Hsu², Sue-Jin Lin², Chou-Ming Cheng¹, Jen-Chuen Hsieh², Low-Tone Ho¹

¹Department of Medical Research and Education, Taipei Veterans General Hospital, Taipei, Taiwan, Taiwan; ²Institute of Brain Science, National Yang-Ming University, Taipei, Taiwan, Taiwan

Structural MRI and functional MR data with motor task of right index were obtained from fourteen normal subjects. Thalamal parcellation by probabilistic diffusion density tractography (PDD) was performed with two protocols. Protocol I applied the Brodmann areas 1-6 as targets in normalized space. And protocol II used the central correlates of motor fMRI as target. Two similarity indices of thalamus parcellation were calculated as SI(BA1-6) = 0.56and SI(motor-fMRI) = 0.96 regarding to protocol I and II, respectively. We concluded the PDD-based parcellation of motor thalamus can be validated by using the fMRI of a simple motor task.

                  1458.     Mapping the Human Connectome at Multiple Scales with Diffusion Spectrum MRI

Leila Cammoun¹, Xavier Gigandet¹, Olaf Sporns², Jean-Philippe Thiran¹, Kim Q. Do³, Philippe Maeder⁴, Reto Meuli⁴, Patric Hagmann^1,4

¹Signal Processing Laboratory 5, Ecole Polytechnique Fédérale de Lausanne, Lausanne, VD, Switzerland; ²Department of Psychological and Brain Sciences, Indiana University, Bloomington, IN, USA; ³Center of Psychiatric Neuroscience, University Hospital Center and University of Lausanne (CHUV), Lausanne, VD, Switzerland; ⁴Department of Radiology, University Hospital Center and University of Lausanne (CHUV), Lausanne, VD, Switzerland

We propose to map the human connectome by constructing normalized whole-brain structural connection matrices derived from diffusion spectrum MRI tractography at 5 different scales. These connection matrices are then examined across scales for several important network characteristics. We show that key network measures can be robustly estimated across multiple scales with results that are consistent with previous single-scale investigations. In particular, we confirm that cortical networks exhibit exponential distributions of node degree and fiber densities, robust small world characteristics, as well as consistent estimates for node centrality at all scales examined.

                  1459.     Cingulum Bundle Asymmetry Predicts Trait Neuroticism: A DTI Study

Kathrine Skak Madsen^1,2, Terry L. Jernigan^1,2, Arnold Skimminge^1,3, Erik Lykke Mortensen^2,4, Gitte M. Knudsen^2,5, William F.C. Baaré^1,2

¹Danish Research Center for Magnetic Resonance, Copenhagen University Hospital, Hvidovre, Copenhagen, Denmark; ²Center for Integrated Molecular Brain Imaging, Copenhagen, Denmark; ³DTU Informatics, Technical University of Denmark, Lyngby, Denmark; ⁴Department of Health Psychology, University of Copenhagen, Copenhagen, Denmark; ⁵Neurobiology Research Unit, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark

Amygdala and subgenual cingulate are linked to anxiety and mood disorders, for which the trait neuroticism is a risk factor. Left and right subgenual cingulate functional imbalances may contribute to behavioural and physical symptoms observed in depression. We investigated associations between neuroticism and cingulum FA in 45 healthy adults. DWI images were processed with TBSS to align main fibre tracts and ROIs were drawn in right and left cingulum. As hypothesized, cingulum FA laterality index (asymmetry) significantly predicted neuroticism. It is unclear whether cingulum FA asymmetry is a possible marker of increased risk of developing anxiety and mood disorders.

                  1460.     High Resolution Diffusion-Weighted Imaging Showing Radial Anisotropy in the Human Cortex in Vivo

Robin Martin Heidemann¹, Alfred Anwander¹, Thomas R. Knösche¹, Thorsten Feiweier², Fabrizio Fasano^3,4, Josef Pfeuffer⁵, Robert Turner¹

¹Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany; ²Siemens Healthcare Sector, Erlangen, Germany; ³Fondazione Santa Lucia, Rome, Italy; ⁴Siemens Medical Solutions, Milano, Italy; ⁵Siemens Medical Solutions, Charlestown, MA, USA

High resolution diffusion-weighted imaging is affected by blurring due to T₂* relaxation and geometrical distortions due to off-resonance effects. A combination of a zoomed approach and parallel imaging enables one to achieve high acceleration factors which are essential to obtain high resolution diffusion–weighted images with minimal distortions. With the achieved image quality and an in plane resolution of 1 mm x 1 mm it is possible to show the radial anisotropy of the human cortex in vivo.

                  1461.     Gender Differences in Correlations of Regional White Matter Integrity with Intelligence Factor Scores

Johnny Ng¹, CheukYing Tang^1,2, Emily Eaves¹, Isabella Kanellopoulou², Xinsu Mai¹, David Carpenter¹, David Schroeder³, Roberto Colom⁴, Richard J. Haire^3,5

¹Radiology, Mount Sinai School of Medicine, New York, NY, USA; ²Psychiatry, Mount Sinai School of Medicine, New York, NY, USA; ³Johnson O'Connor Research Foundation, Chicago, IL, USA; ⁴Universidad Autónoma de Madrid (UAM), Spain; ⁵School of Medicine, UC Irvine, Irvine, CA, USA

We studied correlations between regional white matter integrity, using DTI with a Siemens 3T Allegra, and intelligence factor scores with gender effect in 40 control subjects. Fractional anisotropy (FA) and directional color maps were computed using in-house software. Region of Interests were defined on color-coded maps. FA values were extracted and merged with intelligence factor scores for correlation analysis. Significant positive and negative correlations were detected. These findings were consistent with a recent report on DTI/IQ correlations on subjects 5-18 where correlations were negative in males and positive in females as they aged. Our results confirmed these findings into adulthood.

                  1462.     Diffusion Tensor Imaging at 7T: Expectations Vs. Reality Check

Oliver Speck¹, Kai Zhong¹

¹Biomedical Magnetic Resonance, Otto-von-Guericke University, Magdeburg, Germany

In addition to strong T2 weighting, diffusion encoding reduces the signal significantly to encode the direction information. Therefore, DTI is notoriously SNR hungry and the use of very high field strength has been proposed to increase sensitivity. Despite the introduction of 7T, it is still not clear if 7T results in data quality improvement. The SNR gain in DTI measurements at 7T is estimated based on realistic tissue and imaging parameters. Large volume coverage DTI data have been acquired at 3T and at 7T and were compared. With current whole body gradients diffusion imaging at 7T is not superior to 3T.

                  1463.     Defining Arterial Input Function (AIF) in DSC-MRI: From Global to Local

Qing Ji¹, John O. Glass¹, Wilburm E. Reddick¹

¹Radiological Science, St.Jude Children's Research Hospital, Memphis, TN, USA

We propose a novel method to automatically extract local AIF from T2* weighted perfusion MRI. The local AIF was modeled as the convolution of a global AIF with a vascular transport function and incorporated into a pharmacokinetic model to fit the concentration-time course of the image voxels. We examined ten DSC perfusion MRIs from pediatric brain tumor patients and report initial results demonstrating that the proposed method can fit most voxels well and reconstructed local AIF maps not only show the time delay and dispersion of local vascular features, but also the typical cerebral blood flow pattern.

                  1464.     DSC-MR Perfusion: Leave Tracer Recirculation Alone

Jayme Cameron Kosior^1,2, Richard Frayne²

¹Electrical and Computer Engineering, University of Calgary, Calgary, AB, Canada; ²Seaman Family MR Research Centre, Foothills Medical Centre, Calgary, AB, Canada

A common misconception is that indicator dilution theory cannot be used to derive perfusion parameters such as cerebral blood flow (CBF) and cerebral blood volume (CBV) if tracer recirculation is present in dynamic susceptibility contrast MR perfusion data. Here, we show that it is unnecessary to remove tracer recirculation from DSC-MR data in order to derive perfusion parameters.

                  1465.     Improved Assessment of Regional Cerebral Blood Flow by Dynamic Susceptibility Contrast MRI Using a Kernel-Based Deconvolution Approach

Denis Peruzzo¹, Gianluigi Pillonetto¹, Alessandra Bertoldo¹, Claudio Cobelli¹

¹Department of Information Engineering, University of Padova, Padova, Italy

A deconvolution operation must be performed to obtain the residue function (R(t)) in DSC-MRI images quantification. In this study, a kernel based deconvolution approach is proposed and validated on both simulated and clinical data. It tackles the problem in a fully Bayesian framework and includes information on both R(t) continuity and on the system BIBO stability. It has been shown to provide more physiological R(t) estimates and more accurate CBF values than SVD and cSVD. Furthermore, not only is DNP insensitive to the delay between the AIF and the C(t), but it can also estimate it.

                  1466.     Can a Human Operator Be Replaced by a Computer for Processing of Bolus-Tracking Perfusion Data?

Matus Straka¹, Michael Mlynash², Greg Zaharchuk¹, Gregory W. Albers², Roland Bammer¹

¹Lucas Center, Department of Radiology, Stanford University, Stanford, CA, USA; ²Stroke Center, Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA, USA

Bolus-tracking DSC-MRI PWI is an important technique in acute stroke, but its use in clinical routine is hampered by need of manual processing. We have developed a fully automated system aimed on perfusion processing. A key part of the system is the automated selection of AIF and VOF signals in the data. In this study, we compared manual and automatic selections on 30 cases with focus on noisy data and data with motion. The results indicate high success (>90%) rate of the system on various bolus-tracking datasets and allow usage of such algorithm in clinical routine.

                  1467.     Estimation of CBF Values Using Multi-Echo DSC-MRI:  a Comparison with a Xenon CT

Matus Straka¹, Greg Zaharchuk¹, Rexford David Newbould², Gregory W. Albers³, Michael E. Moseley¹, Roland Bammer¹

¹Lucas Center, Department of Radiology, Stanford University, Stanford, CA, USA; ²GlaxoSmithKline, London, UK; ³Stroke Center, Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA, USA

Standard PWI acquisitions using single-echo EPI suffer from various errors (e.g. vascular signal clipping and counfound determination of quantitative perfusion values). Advanced acquisition schemes (e.g. PERMEATE) as well as corrections for partial volume effect and susceptibility effect of tracers in bulk blood were proposed to mitigate the problems. In this study, we have compared CBF perfusion maps computed from multi-echo parallel EPI sequences with values from XeCT CBF maps. We conclude that multi-echo acquisition contribute to better estimates of the quantitative parameter, but the improved acquisition opened a whole new set of challenges that were important before.

                  1468.     Limitations of a Multiplicative Correction of Partial Volume Effects on the Arterial Input Function in Bolus-Tracking Perfusion

Adam Espe Hansen¹, Henrik Pedersen¹, Egill Rostrup¹, Henrik BW Larsson¹

¹Functional Imaging Unit, Glostrup Hospital, Glostrup, Denmark

The partial volume effect (PVE) on the arterial input function (AIF) remains a major obstacle to absolute quantification of cerebral blood flow (CBF) using MRI. This study evaluates the validity and performance of a commonly used multiplicative rescaling of the AIF to correct for the PVE. In a group of six patients, perfusion imaging was performed using a T₁-weighted approach. Various degrees of PVE were induced on the AIF and subsequently corrected using a multiplicative AIF rescaling. Our results show that a multiplicative rescaling is not always applicable and can introduce a CBF bias. An easily measurable quantity denoted the tissue signal fraction (TSF) is proposed as a measure of the applicability of a multiplicative rescaling. For the present CBF quantification method a TSF of less than 0.4 results in a CBF bias below 15% after AIF rescaling.

                  1469.     Dynamic Susceptibility MRI with a Pre-Bolus Administration Design for Improved Absolute Quantification of Perfusion

Linda Knutsson¹, Anna Rydhög¹, Danielle van Westen², Stig Holtås², Freddy Ståhlberg^2,3, Ronnie Wirestam¹

¹Department of Medical Radiation Physics, Lund University, Lund, Sweden; ²Department of Diagnostic Radiology, Lund University, Lund, Sweden; ³Department of Medical Radiation Physics, Lund University , Lund, Sweden

Reproducible absolute quantification of cerebral blood volume (CBV) and cerebral blood flow (CBF) by dynamic susceptibility contrast MRI (DSC-MRI) is difficult to achieve, for example, due to partial-volume effects (PVEs). The purpose of this study was to correct for arterial PVEs by rescaling the AIF using a VOF obtained by injecting a fraction of the contrast-agent dose as a pre-bolus. During the pre-bolus passage, a segmented EPI sequence in single-slice mode was used to register the VOF in the superior sagittal sinus. Our results showed that our proposed correction method removed a substantial amount of arterial PVEs.

                  1470.     Estimation of Perfusion and Other Vascular Parameters from First Part of Bolus Passage

Lars G. Hanson¹, Henrik Lund¹, Irene K. Mikkelsen²

¹Danish Research Centre for MR, dept. 340, Copenhagen University Hospital, Hvidovre, Denmark; ²Centre for Functionally Integrative Neuroscience, Århus University Hospital, Århus, Denmark

Vascular properties can be derived from dynamic measures of the

                  1471.     Dose Optimization for Combined Perfusion Weighed Imaging and Contrast Enhanced MRA Using Gadofosveset

Erik Søndergaard Poulsen¹, Aage Kristian Olsen², Dora Zeidler¹, Niels Hjort¹, Leif Østergaard¹

¹Center of Functionally Integrative Neuroscience (CFIN), University of Aarhus, Aarhus, Denmark; ²PET-center, Aarhus University Hospital, Denmark

We optimized the dose of novel Gd-based, intravascular contrast agent gadofosveset trisodium (Vasovist®, Bayer Schering Pharma. Berlin, Germany) for dynamic susceptibility contrast (DSC) MRI in the brain. In 40 kg anesthetized pigs, a dose of 0.0916 mmol/kg was shown to generate a similar signal drop as a standard 0.1 mmol/kg Gd-chelate (Gadovist 1.0®, Bayer Schering Pharma. Berlin, Germany) while generating good CNR on steady state MRA.

                  1472.     Quantification of Vessel Permeability by Modeling Contrast Agent Extravasation in Dynamic Susceptibility Contrast MRI of Brain Tumors

Yi-Ying Wu¹, Wei-Shan Yang^2,3, Yuan-Yu Hsu⁴, Ho-Ling Liu^2,5

¹Institute of Medical Physics and Imaging Science, Chang Gung University, Kwei-Shan , Tao-Yuan, Taiwan; ²Institute of Medical Physics and Imaging Science, Chang Gung University, Kwei-Shan, Tao-Yuan, Taiwan; ³Department of Radiology, Cheng Hsin Rehabilitation Medical Center, Taipei, Taiwan; ⁴Department of Medical Imaging, Buddhist Tzu Chi General Hospital, Taipei, Taiwan; ⁵MRI Center, Chang Gung Memorial Hospital, Tao-Yuan, Taiwan

Disruption of BBB in brain tumors can cause errors in perfusion measurements using DSC MRI. This study proposed a model that takes both T1 and T2 effect of the contrast extravasations into account and at the same time incorporates the parameter of permeability-surface-area-product (PS). This model was applied in three DSC datasets of brain tumors at 3T. The resultant PS ranged from 0.28 to 0.74 min-1 in tumors, which was greater than in normal tissues. Tumor/white matter blood volume ratios were corrected (3.5-7.4 before and 1.6-4.4 after correction) by fitting DSC time curves to the proposed model.

                  1473.     Quantitative OEF Determination in Tumor Patients Using Additional DSC Measurements

Moritz Mie¹, Maja Sohlin², Johann Scharf³, Lothar Rudi Schad⁴

¹Computer Assisted Clinical Medicine, Faculty of Medicine Mannheim,, University of Heidelberg, Mannheim, Germany; ²Medical Physics in Radiology, DKFZ, Heidelberg, Germany; ³Department of Neuroradiology, University Hospital, Mannheim, Germany; ⁴Computer Assisted Clinical Medicine, Faculty of Medicine Mannheim, University of Heidelberg, Mannheim, Germany

Tissue oxygenation is a very important factor in the field of neuroradiology. With the assistance of the oxygen extraction fraction (OEF) an estimation of tissue viability should be possible. In this work, we improved the present technique by using an additional independent dynamic susceptibility contrast (DSC) measurement that directly gives the amount of cerebral blood volume (CBV) which is an important parameter for stabilizing the OEF calculation. With this technique a difference in OEF between a healthy brain area and a tumorous one is observed.

                  1474.     Normative Blood Flow Values in the Posterior Fossa Using Quantitative Spin-Echo DSC Perfusion MRI

Jessy J. Mouannes¹, Anahita Aghaei-Lasboo², Amir H. Yassari³, Anindya Sen², Aaron Skolnik³, Shahram Rahimi², Timothy J. Carroll^2,4, Bernard R. Bendok⁵, Matthew T. Walker², Sandra W. Horowitz², Ali Shaibani²

¹Biomedical Engineering, Northwestern University , Chicago, IL, USA; ²Radiology, Northwestern University, Chicago, IL, USA; ³Feinberg School of Medicine, Northwestern University, Chicago, IL, USA; ⁴Biomedical Engineering, Northwestern University, Chicago, IL, USA; ⁵Neurological Surgery, Northwestern University, Chicago, IL, USA

The interest in cerebral perfusion imaging has increased in recent years, with the aim of accurately detecting brain tissue at risk of infarction. These efforts have resulted in the establishment of normal values for cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT), for the supratentorial section of the brain. However, without a quantitative understanding of normal flow values in the posterior fossa, it is difficult to make judgments on issues such as cerebrovascular reserve or chronic ischemia. Therefore, we have evaluated normative “quantitative” perfusion values for the posterior fossa in adults using the Bookend technique.

                  1475.     Dynamic Contrast Enhanced Whole Brain Perfusion Using a Rapid 3D T₁-Weighted Sequence at 7T

Paul S. Morgan^1,2, Emma C. Tallantyre³, Ali Al-Radaidah³, Jennifer E. Dixon⁴, Matthew J. Brookes⁴, Nikos Evangelou³, Peter G. Morris⁴

¹Radiology & Radiological Sciences, Medical University of South Carolina, Charleston, SC, USA; ²Academic Radiology, University of Nottingham, Nottingham, UK; ³Clinical Neurology, University of Nottingham, Nottingham, UK; ⁴Sir Peter Mansfield MR Centre, University of Nottingham, Nottingham, UK

7T has shown potential in imaging the human brain. We investigated the feasibility of acquiring whole brain perfusion data during administration of a bolus of gadolinium-based contrast agent at 7T using a 3D T₁-weighted technique previously demonstrated at lower field. Successful data were acquired on three patients with multiple sclerosis, yielding perfusion values for white and gray matter in the range obtained by other perfusion studies, indicating that this technique may be performed successfully at 7T.

                  1476.     Quantitative Cerebral Perfusion in Rodents Assisted by Susceptibility Weighted Imaging

Rui Liu¹, Renjie He², Kurt H. Bockhorst², Venkata K. Mogatadakala², Ponnada A. Narayana²

¹Department of Electrical and Computer Engineering, University of Houston, houston, TX, USA; ²Department of Diagnostic and Interventional Imaging, University of Texas Medical School at Houston, Houston, TX, USA

Synopsis: A method for accurate determination of the perfusion parameters based on dynamic susceptibility contrast MRI is proposed and applied to determine the hemodynamic parameters in a rat brain. Our algorithm is based on the singular valued decomposition (SVD) technique. In addition, we registered SWI images with gradient-echo EPI images to identify and exclude venous structures for improved estimation of hemodynamic parameters. The hemodynamic parameters calculated using our procedure agrees with those determined using the microsphere technique, considered to be the “gold standard”.

                  1477.     Gas-Filled Microbubbles as Intravascular Susceptibility Contrast Agent for Brain MRI

Jerry S. Cheung^1,2, April M. Chow^1,2, Ed X. Wu^1,2

¹Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Hong Kong SAR, China; ²Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong SAR, China

Gas-filled microbubbles have the potential to become a unique MR contrast agent due to their magnetic susceptibility effect, biocompatibility and localized manipulation via ultrasound cavitation. In this study, custom-made albumin-coated microbubbles and a commercially available lipid-based clinical ultrasound contrast agent SonoVue® were investigated with in vivo dynamic brain MRI in Sprague-Dawley rats at 7 Tesla. The results indicate that microbubbles can serve as an intravascular contrast agent for brain MRI at high field. Such microbubble MRI has the potential to provide real-time MRI guidance in various microbubble-based drug delivery and therapeutic applications.

                  1478.     Detection of Pulmonary Embolism with Hyperpolarized 3He MRI: A Comparison of PO2-Based and Susceptibility-Based Techniques

Michelle E. Law¹, Jiangsheng Yu¹, Stephen Kadlecek¹, Kiarash Emami¹, Masaru Ishii², John MacDuffie-Woodburn¹, Matthew Stetz¹, Rahim R. Rizi¹

¹Radiology, University of Pennsylvania, Philadelphia, PA, USA; ²Department of Otolaryngology, Head and Neck Surgery, Johns Hopkins University, Baltimore, MD, USA

Hyperpolarized 3He MRI has been applied to diagnosis pulmonary emboli. In this work, we present a comparison of pO2-based and susceptibility-based hyperpolarized 3He MRI techniques for the detection of pulmonary emboli in a pig model. The experiment results show that the pO2-based technique is more sensitive than the susceptibility-based technique.

                  1479.     An Automated Method for Determination of Arterial Input and Venous Output Function Using Perfusion Parametric Joint Histogram Analysis

Hiroyuki Kabasawa¹, Tetsuji Tsukamoto¹

¹Japan Applied Science Laboratory, GE Yokogawa Medical Systems, Hino-shi, Tokyo, Japan

The automated arterial input and venous output function (AIF and VOF) is crucial to improve stroke diagnosis workflow and to reduce the variation of perfusion analysis result. The quality of AIF and VOF is also critical for perfusion quantification. We have developed the automated AIF/VOF detection algorithm based on the perfusion parametric joint histogram analysis. We showed that the VOF detection accuracy was significantly improved, by adding the averaged tracer concentration after bolus passages information into the joint histogram analysis.

                  1480.     Intravascular Water Molecule Lifetime in the Japanese Macaque Brain

Jeffrey Moses Njus¹, James R. Pollaro¹, Mathew T. Snodgrass¹, John Cunneen¹, Ethan Muldoon¹, Vincent B. Warren², Xin Li¹, Charles S. Springer¹, Steven G. Kohama², William D. Rooney¹

¹Advanced Imaging Research Center, Oregon Health & Science University, Portland, OR, USA; ²Oregon National Primate Research Center, Beaverton, OR, USA

The purpose of this study was to investigate brain intravascular water molecule lifetime estimation using a dynamic contrast enhanced technique. MRI data were collected at 3T in the Japanese macaque. Gadoteridol (Gd) was administered and whole-brain quantitative R₁ maps were collected using a sparse pharmacokinetic temporal sampling scheme during the contrast washout period. We compare intravascular water lifetimes extracted with and without accounting for Gd extravasation during the time series.

                  1481.     Simultaneous Imaging of Absolute CBF Change and BOLD with Saturation-Recovery-T1 MRI Approach Under Ischemia and Hypercapnia

Xiao Wang¹, Xiao hong Zhu¹, Yi Zhang¹, Wei Chen¹

¹Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN, USA

Apparent T1 is sensitive to cerebral perfusion, thus, CBF can be imaged by MR-based arterial spin labeling techniques. In this study, we proposed an alternative approach based on the saturation-recovery T1 imaging method for simultaneously measuring absolute CBF change (∆CBF) and BOLD. This perfusion approach was validated by examining the relationship between the simultaneously-measured ƒ´CBF using the MRI approach and relative percent CBF change using LDF in the rat brain under ischemia and hypercapnia conditions. The results suggest that the measured change in apparent T1 was tightly correlated to the absolute CBF increase during hypercapnia and decrease during ischemia. This perfusion approach, thus, should provide a useful, robust MRI tool for noninvasively imaging absolute CBF change and BOLD associated with brain physiology, function and viability.

                  1482.     Rapid and Direct Quantification of Longitudinal Relaxation Time (T1) in Look-Locker Sequences Using an Adaptive Neural Network

Hassan Bagher-Ebadian^1,2, Ramesh Paudyal^1,2, Tom Mikkelsen³, Quan Jiang¹, James Russel Ewing^1,2

¹Neurology, Henry Ford Hospital, Detroit, MI, USA; ²Physics, Oakland University, Rochester, MI, USA; ³Neurosergery, Henry Ford Hospital, Detroit, MI, USA

In this study an adaptive neural network is employed for direct estimation of longitudinal relaxation time (T1) in Look-Locker signals. It is hypothesized that, given a signal generated by a LL model, an ANN could be trained to directly estimate T1. The analytical equation of the Look-Locker signal was considered as the gold standard of training and a set of LL signals for a wide range of T1’s were generated. For each T1 value LL signal inputs were generated by varying the other independent parameters in the synthetic model of signal (T2*, M0 etc).

                  1483.     Accuracy of Cerebral Blood Flow Measurements in Accelerated Dynamic Contrast Enhanced MRI Using k-T SENSE

Henrik Pedersen¹, Adam Espe Hansen¹, Henrik B.W. Larsson¹

¹Functional Imaging Unit, Glostrup Hospital, Glostrup, Denmark

Dynamic contrast enhanced (DCE) MRI represents an attractive technique for quantifying cerebral blood flow (CBF). However, the inherent slow nature of DCE-MRI currently prohibits whole-head imaging of CBF. This study investigates how different degrees of data reduction obtained with k-t SENSE influence CBF measurements in the brain. The results suggest that the optimum combination of training data size and acceleration factor is 11 training profiles and 8x acceleration, resulting in a net acceleration factor of 4.6. In practise, this allows increasing the spatial coverage of DCE-MRI from 4 slices with SENSE to 10 slices with k-t SENSE.

                  1484.     Dynamic Contrast Enhanced (DCE) MRI Metrices as a Predictor of Response in Head and Neck Cancers

Sushma Agrawal¹, Rishi Awasthi², Anup Singh³, Ram Kishore Singh Rathore³, Rakesh Kumar Gupta²

¹Department of Radiotherapy, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, Uttar Pradesh, India; ²Department of Radiodiagnosis, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, Uttar Pradesh, India; ³Department of Mathematics and statistics, Indian institute of technology, Kanpur, Uttar Pradesh, India

DCE imaging prior to radiotherapy and three months of completion of radiotherapy were performed in 21 patients of locally advanced head and neck cancers.The DCE MRI parameters in terms of tissue blood flow (TBF), tissue blood volume (TBV), corrected TBV, bolus arrival time (BAT) and b were correlated with T, N, stage group of the patient and with response to treatment. TBF, TBV and corrected TBV were higher for higher T stage, but not for N stage, and overall stage group .These parameters were higher for complete responders than partial responders at both primary and nodes. Our study reflects TBF and TBV as predictors of outcome in head and neck cancer patients but needs validation in more patients to get a more robust conclusion

                  1485.     Concurrent Measurement of Brain Perfusion, Blood Volume and Blood Brain Barrier Permeability Using Dynamic Contrast Enhanced T₁ -Weighted MRI

Henrik BW Larsson¹, Frederic Courivaud², Egill Rostrup¹, Adam Espe Hansen¹

¹Functional Imaging Unit, Glostrup Hospital, Glostrup, Denmark; ²The Interventional Centre, Rikshospitalet, Oslo, Norway

The measurement of brain perfusion (CBF) and cerebral blood volume (CBV) is important when diagnosing and treating vascular, degenerative and neoplastic diseases. These diseases are often associated with an increase of blood brain barrier (BBB) permeability. Despite the widespread use of MR perfusion imaging based on bolus tracking a concurrent estimation of CBF, CBV and permeability has proved difficult to achieve. The present study shows that brain perfusion, brain blood volume and blood brain barrier permeability can be obtained concurrently from dynamic contrast enhanced T₁ -weighted perfusion imaging. Perfusion was estimated by Tikhonov’s deconvolution method and blood volume and permeability were estimated by using Patlak’s method in 10 patients with brain tumors. The results point to the importance of considering the effect of BBB leakage on the CBV estimation.

                  1486.     Enhancement of Gas-Filled Microbubble Magnetic Susceptibility by Iron Oxide Nanoparticles

April M. Chow^1,2, Jerry S. Cheung^1,2, Ed X. Wu^1,2

¹Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Hong Kong SAR, China; ²Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong SAR, China

Gas-filled microbubbles possess the ability to be an MR susceptibility contrast agent due to the induction of large local magnetic susceptibility differences by the gas-liquid interface. However, microbubble susceptibility effect is relatively weak when compared with other intravascular MR susceptibility contrast agents. In this study, we demonstrated that microbubble susceptibility effects can be improved by embedding and entrapping iron oxide nanoparticles, and hence microbubbles can be monitored with high sensitivity and low concentrations under MRI.

                  1487.     Single-Shot Look Locker T1 Mapping with Golden Angle Radial Sampling for Free-Breathing Liver DCE-MRI in Rats at 1.5 T

Andreas Steingoetter¹, Jonas Svensson^1,2, Rickmer Braren³, Rene Botnar^1,4, Stefanie Remmele⁵

¹Department of Nuclear Medicine, Klinikum rechts der Isar, Technische Universität München, Munich, Germany; ²Department of Medical Radiation Physics, Malmoe University Hospital, Lund University Malmoe, Malmoe, Sweden; ³Department of Radiology, Klinikum rechts der Isar, Technische Universität München, Munich, Germany; ⁴Division of Imaging Sciences, King’s College London School of Medicine, London, UK; ⁵Philips Research Europe-Hamburg, Hamburg, Germany

A 2D single-shot Look-Locker T1 mapping technique (LLRGC) applying golden angle radial sampling and dedicated contrast enhancing k-space filter has recently been proposed for DCE-MRI studies. Here, we evaluate this technique for non-triggered and free-breathing DCE-MRI experiments in rats. T1 variability, flip angle dependency and motion sensitivity were analyzed in-vitro and in-vivo. Modelling capability of acquired concentration curves was confirmed by calculating Ktrans and ve. Phantom T1 values match reference values and show no flip angle dependency. No impairing motion artefacts are observed in images and T1 maps of rat abdomen. Determined Ktrans and ve values correspond to literature values.

                  1488.     Developmental Analysis of Placental Vascularization Using Dynamic Contrast- Enhanced MRI

Stav Sapoznik¹, Vicki Plaks¹, Elina Berkovitz², Rebecca Haffner-Krausz², Michal Neeman¹

¹Biological Regulation, Weizmann Institute of Science, Rehovot, Israel, Israel; ²Veterinary Resources, Weizmann Institute of Science, Rehovot, Israel

The importance of the placental circulation has long been recognized and is exemplified by the correlation of fetal weight with placental size and blood flow. In the current study we applied macromolecular contrast-enhanced MRI for in utero assessment of placental function along pregnancy in mice. We were able to assess placental blood volume fraction, rate of contrast material enhancement, placental volume and fetal length. We evaluated normal placentas at different developmental stages, as well as strain specific differences. Additionally, we studied placental function during fetal resorption and the function of tetraploid placenta in complementation rescue of genetically modified mice.

                  1489.     Factor Analysis in Segmentation of 4D DCE-MRI Renal Studies

Borys Shuter^1,2, Voreak Suybeng³, David A. Stringer⁴, Marica Cutajar⁵, Thomas Dissing⁶, Anni Eskild-Jensen⁷, Michael Pedersen⁸, Jørgen Frøkiær⁶, Jens Christian Djurhuus⁶, Ashraf Kassim³, Shih-Chang Wang¹, Isky Gordon⁵

¹Diagnostic Radiology, National University of Singapore, Singapore, Singapore; ²Diagnostic Imaging, National University Hospital, Singapore; ³Electrical and Computer Engineering, National University of Singapore, Singapore; ⁴KK Women's and Children's Hospital, Singapore; ⁵UCL Institute of Child Health, London, UK; ⁶Institute of Clinical Medicine, University of Aarhus, Denmark; ⁷Department of Nuclear Medicine, Aarhus University Hospital, Denmark; ⁸Institute of Clinical Medicine, University of Aarhus,, Denmark

Temporal information inherent in 4D DCE-MRI may be utilised to segment anatomy of clinical interest. Factor analysis is shown to be able to isolate renal compartments and other abdominal and thoracic organs in clinical studies and a porcine model of renal obstruction.

                  1490.     DCE MRI Pixel-By-Pixel Quantitive Curve Pattern Analysis (CPA)

Junyu Guo¹, Wilburn E. Reddick¹

¹Radiological Sciences, St. Jude Children's Research Hospital, memphis, TN, USA

A novel Curve Pattern Analysis (CPA) method is presented for DCE-MRI data processing. The CPA method characterizes and quantifies the DCE-MRI signal curves without prerequisites such as AIF and T1 measurement. The simulations show that the CPA parameters are stable and approximately insensitive to the baseline T1 value, TR and flip angle. In vivo study shows that the CPA parameter &[kappa] is very sensitive to the curve pattern and well correlated with the kinetic parameter kep. This method therefore could have a higher repeatability by eliminating effects from some variation factors, e.g. AIF and T1.

                  1491.     A Precise Model for Arterial Input Functions of First Pass DCE-MRI

Jeiran Jahani¹, Glyn Johnson²

¹Bioimaging, New York University, New York, USA; ²Bioimaging, New York University, New York, USA

                  1492.     Orthogonal Diffusion Anisotropy Measurements in the Dorsal Third Ventricle of Adult Rat Brain Reveal Cerebrospinal Fluid Flow

Laura Nieto-Charques¹, Pilar López-Larrubia¹, Sebastián Cerdán¹

¹Instituto de Investigaciones Biomédicas Alberto Sols CSIC-UAM, Madrid, Spain

Diffusion Weighted Magnetic Resonance Imaging (DW-MRI) provides information on the microstructure of tissues and its changes. However, the calculated ADC values may contain contributions from additional translational motions or flow. To investigate this aspect we measured water ADC in three orthogonal directions of the Dorsal Third Ventricle of rat brain during a live-sacrifice and low-high b value paradigms. We found that CSF flow through the head-feet direction of the D3V increased significantly the ADC determined in this direction for both low and high b value sequences. An isotropic diffusion pattern is found when impeding CSF flow by sacrificing the animals.

                  1493.     Deletion of the Brain-Specific Link Protein BRAL-1 Facilitates Extracellular Diffusion in the Mouse Corpus Callosum

Ivan Vorisek^1,2, Lydia Vargova^2,3, Lesia Dmytrenko¹, Yoko Bekku⁴, Toshitaka Oohashi⁴, Eva Sykova^1,2

¹Department of Neuroscience, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, v.v.i., Prague, Czech Republic; ²Center for Cell Therapy and Tisue Repair, Charles University, 2nd Medical Faculty, Prague, Czech Republic; ³Department of Neuroscience, Charles University, 2nd Medical Faculty, Prague, Czech Republic; ⁴Department of Mollecular Biology and Biochemistry, Okayama University Graduate School of Medicine and Dentistry, Okayama, Japan

Besides morphological techniques, the structure of the nervous tissue may be revealed by the diffusion of substances in the extracellular space (ECS). The efficacy of extrasynaptic transmission between neurons and between neurons and glia is based on the diffusion of neuroactive substances in the ECS and depends on the diffusion properties of the ECS. Our previous studies revealed that changes in the extracellular matrix substantially affect the diffusion properties of nervous tissue. In the present study we examined three parameters describing the diffusion of molecules and neuroactive substances in the cortex and corpus callosum of BRAL1 positive and negative mice.

                  1494.     In Vivo Diffusion Tensor Magnetic Resonance Imaging and Fiber Tracking of the Mouse Brain

Laura-Adela Harsan¹, Dominik Paul¹, Susanne Schnell¹, Bjorn W. Kreher¹, Juergen Hennig¹, Jochen F. Staiger², Dominik von Elverfeldt¹

¹Department of Diagnostic Radiology, University Hospital Freiburg, Medical Physics, Freiburg, Germany; ²Department of Neuroanatomy, Institute for Anatomy and Cell Biology, Center for Neuroscience, Freiburg, Germany

In vivo DT-MRI and fiber tracking was used in the present study to describe major white matter fiber tracts of the mouse brain and also to identify for the first time non-invasively the rich connectivity between the amygdala and different brain regions. Beside the standard fiber tracking procedure we generated probability maps of connectivity with which it was possible to investigate – in a statistical sense - all possible connecting pathways between two seed points. We show here applications to determine the connection probability between regions belonging to the visual or limbic systems.

                  1495.     Diffusion Tensor Image Guided Histological Assessment of a Kainic Acid Rat Epilepsy Model Ex Vivo Utilizing Tract-Based Spatial Statistics Analysis

Alejandra Sierra¹, Kimmo Lehtimäki², Teemu Laitinen¹, Jari Nissinen¹, Asla Pitkänen^1,3, Olli Gröhn¹

¹Department of Neurobiology, A.I. Virtanen Institute, University of Kuopio, Kuopio, Finland; ²Department of Biotechnology and Molecular Medicine, A.I. Virtanen Institute, University of Kuopio, Kuopio, Finland; ³Department of Neurology, Kuopio University Hospital, Kuopio, Finland

Epilepsy is a challenging disease for imaging due to heterogeneous, widespread and non-focal changes in the brain tissue. The present study diffusion tensor imaging (DTI) and tract-based spatial statistics (TBSS) analysis provides "anatomics" of the brain pathology during experimental epileptogenesis, revealing areas involved in the epileptogenic process in a kainic acid animal model. This technique has a great potential to serve as a robust screening method to guide tedious histological analysis aimed to reveal cellular alterations of neuronal pathways.

                  1496.     MRI Evaluation of Selective Disruption of the Blood-Brain Barrier by Photochemical Internalization

Michelle Zhang¹, Steen J. Madsen¹, Henry Hirschberg^1,2, H Michael Gach³

¹Health Physics, University of Nevada Las Vegas, Las Vegas, NV, USA; ²Beckman Laser Institute, University of California Irvine, Irvine, CA, USA; ³Research Imaging Facility, Nevada Cancer Institute, Las Vegas, NV, USA

T2- and T1-weighted post-contrast MRI scans were acquired at 7 T to evaluate blood brain barrier (BBB) disruption from treatment-induced edema and contrast volumes. Photochemical internalization (PCI) treatment, coupling the macromolecule Clostridium perfringens (Cl p) epsilon prototoxin with AlPcS2a-photodynamic therapy (PDT), was performed on non-tumor bearing inbred Fischer rats. The result of BBB disruption from PCI was compared with a control group receiving PDT-only. PCI was found to be highly effective for inducing selective and localized disruption of the BBB. The extent of BBB opening peaked on day 3 and was completed restored by day 18 after PCI.

                  1497.     Crossing Fibers in Lateral White Matter of the Cervical Spinal Cord Detected with Diffusion MRI  in Monkey Postmortem

Henrik Lundell^1,2, Tim Dyrby¹, Maurice Ptito^1,3, Jens Bo Nielsen⁴

¹Danish Research Centre for Magnetic Resonance, Copenhagen University Hospital, Copenhagen, Denmark; ²Department of Exercise and Sport Sciences, University of Copenhagen, Copenhagen, France, Denmark; ³School of Optometry, Univ Montreal, Montreal, QC, Canada; ⁴Department of Exercise and Sport Sciences, University of Copenhagen, Copenhagen, Denmark

Mapping the white matter configuration of the spinal cord is of interest for understanding superspinal contribution to the generation of motion and coordination of muscles. Postmortem diffusion weighted MRI is a potent technique to investigate the microstructure of neuronal tissue. We have investigated fiber directions of the spinal cord in monkey using DT, Q-ball and PAS. Crossing fiber structures in the corticospinal tract was found using multi-fiber reconstruction techniques with good correlation to histological findings of terminating fibers.

                  1498.     Comparison of Cerebral Blood Flow as Measured by Arterial Spin Labeling and Cerebral Blood Volume as Measured by Micro-CT Imaging Over Regions of the Mouse Brain

Brige Paul Chugh¹, Jason P. Lerch¹, Lisa X. Yu¹, R Mark Henkelman¹, John G. Sled¹

¹Toronto Centre for Phenogenomics, Mouse Imaging Centre, The Hospital for Sick Children, Toronto, Ontario, Canada

We developed an efficient imaging protocol to study the relationship between cerebral blood volume (CBV) and cerebral blood flow (CBF) over regions of the entire mouse brain, which may in future be applied to phenotype models of neurovascular disease. We performed a study that compared normative values of CBV and CBF over 13 mouse brain regions and over the cerebral cortex. The CBF was imaged using 3D arterial spin labeling and these images were co-registered to CBV images determined by a micro-CT protocol. This method could be useful for characterizing regional differences in vascularity in mouse models of cerebrovascular disease.

                  1499.     Temporal Tissue Assessment in Non-Human Primate Cerebral Ischemia Using Diffusion-Weighted MR Imaging and ISODATA Cluster Analysis

Mark J.R.J. Bouts^1,2, Ona Wu^1,3, Rick M. Dijkhuizen², Alex J. de Crespigny^1,3, Helen E. D'Arceuil^1,3

¹Athinoula A. Martinos center for biomedical imaging, Massachusetts General Hospital, Charlestown, MA, USA; ²Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands; ³Radiology, Massachusetts General Hospital, Charlestown, MA, USA

Non-human primate experimental stroke models allow for studying precisely timed evolutionary DWI stroke patterns, which appear similar to those seen in human stroke, without temporal MRI sampling restriction. In regional analysis partial volume artifacts and non-significant regional signal variations within the lesions can bias the analysis outcome.Therefore, in this study we applied an ISODATA analysis to elucidate on a voxel-by-voxel basis multiple evolutionary ADC/FA signatures in permanent vs transient MCA occluded macaque brains. Five distinct signatures were distinguished demonstrating the potential of voxel-by-voxel analysis in staging, identifying and quantifying ischemic tissue damage as a result of stroke.

                  1500.     Cerebral Hypoxia-Ischemia in Neonates as a Model of Ischemic Injury to Study MR Diagnosis of Descending Corticospinal Tract Degeneration

Sanju Lama¹, Min Qiao², Amy Ng¹, Delphi Barua¹, Dave Kirk¹, Tad Foniok², Ursula Irene Tuor^1,2

¹Experimental Imaging Center and Faculty of Medicine, University of Calgary, Calgary, AB, Canada; ²Institute for Biodiagnostics (West), National Research Council, Calgary, AB, Canada

Wallerian degeneration of the descending corticospinal tract (DCST) has been reported as a detection of increased signal intensities in Diffusion weighted imaging (DWI) following pediatric stroke. We hypothesized that a neonatal animal model of cerebral hypoxia ischemia and MRI may also detect such MR intensity changes. Seven day old rats were subjected to cerebral hypoxia-ischemia. Following the injury, T2 and DWI increased significantly in ipsilateral regions of the DCST including the cerebral peduncle and internal capsule.This is comparable to observations made clinically indicating the availability of an animal model to investigate details of MR diagnosis of CNS pre/Wallerian degeneration.

                  1501.     DTI Eigenvalues in Grey Matter: A Songbird's Perspective

Geert De Groof¹, Marleen Verhoye^1,2, Alexander Leemans³, Marcel Eens⁴, Veerle M. Darras⁵, Annemie Van der Linden¹

¹Bio-Imaging Lab, University of Antwerp, Antwerp, Belgium; ²Vision Lab, University of Antwerp, Antwerp, Belgium; ³Cardiff University Brain Research Imaging Centre (CUBRIC), Cardiff University, Cardiff, UK; ⁴Ethology Research Group, University of Antwerp, Antwerp, Belgium; ⁵Animal Physiology and Neurobiology Section, K.U. Leuven, Leuven, Belgium

                 1509.     Delayed Arrival of Arterial Blood Measured with Arterial Spin Labeling in Patients with a Symptomatic Carotid Artery Stenosis

Reinoud Pieter Harmen Bokkers¹, H. Bart van der Worp², Willem P. Mali¹, Jeroen Hendrikse¹

¹Department of Radiology, UMC Utrecht, Utrecht, Netherlands; ²Department of Neurology, UMC Utrecht, Utrecht, Netherlands

Arterial spin labeling (ASL) with image acquisition at multiple delay times is able to measure the temporal dynamics of arterial blood inflow in addition to cerebral blood flow. The purpose of this study was to investigate the effect of a symptomatic stenosis in the internal carotid artery on the arrival of arterial blood measured with ASL. Herein, we found a delayed arrival of arterial blood in the hemisphere ipsilateral to ICA stenosis. ASL measurements of arterial blood inflow may provide valuable information on the hemodynamic changes in patients with an ICA stenosis.

                  1510.     Characterising the Origin of the Arterial Spin Labelling Signal in MRI Using a Multi-Echo Acquisition Approach

Jack A. Wells^1,2, Mark F. Lythgoe^2,3, Mankin Choy^2,3, David Gadian², Roger Ordidge¹, David L. Thomas¹

¹Advanced MRI Group, University College London, London, UK; ²RCS Unit of Biophysics, UCL Institute of Child Health, London, UK; ³Centre for Advanced Biomedical Imaging, University College London, London, UK

ASL provides a means of isolating the MR signal from arterial blood water in the brain. We have measured the transverse decay of the ASL signal over a range of bolus durations and delivery times to estimate the dynamic origin of nutritive flow within the extra and intracellular tissue space in the rat brain. By taking measurements with and without vascular crusher gradients we have calculated the extent of the perfusion weighted signal originating from the cerebral vasculature. We hope that this technique may be useful for future application in animal models of disease to better understand the relationship between perfusion and pathology.

                  1511.     Reliable Isolation of the Intravascular Contribution in Arterial Spin Labelling MRI

Michael A. Chappell¹, Bradley J. MacIntosh¹, Nicola Filippini^1,2, Matthias Günther^3,4, Clare E. Mackay^1,2, Peter Jezzard¹, Mark W. Woolrich¹

¹Centre for Functional MRI of the Brain, University of Oxford, Oxford, UK; ²Department of Psychiatry, University of Oxford, UK; ³Univeristy Hospital Mannheim, University of Heidelberg; ⁴Advanced MRI Technologies, Sebastopol, CA

Multi-inversion time ASL is a potentially rich source of information about the cerebral blood flow, providing more than just CBF measurement alone. This study demonstrates that it is feasible to extract the intravascular contribution in ASL data that has not been subject to flow suppression. A probabilistic approach is used that allows Automatic Relevancy Determination to be implemented, avoiding over fitting with an arterial blood signal where none exists.

                  1512.     Optimization and Implementation of Vessel Suppression Preparation for ASL MRI

Weiying Dai^1,2, Philip M. Robson^1,2, Ajit Shankaranarayanan³, David C. Alsop^1,2

¹Radiology, Beth Israel Deaconess Medical Center, Boston, MA, USA; ²Radiology, Harvard Medical School, Boston, MA, USA; ³Applied Science Laboratory, GE Healthcare, Menlo Park, CA, USA

The presence of intravascular signal can have undesirable effects on image quality and perfusion values with arterial spin labeling (ASL) techniques. Bipolar gradients have been employed to attenuate the flowing labeled spins within spin or gradient echo echoplanar images. However, the insertion of bipolar gradients can be difficult or impossible in multiple RF refocused imaging sequences such as FSE and balanced SSFP. As an alternative, we optimized and implemented a preparation sequence before the image acquisition to eliminate the fast flowing spins. This preparation can be flexibly combined with any image acquisition.

                  1513.     Dispersion of a Short ASL Bolus Along the Arterial Tree

Matthias Günther¹

¹Neurology department, University Hospital Mannheim, University Heidelberg, Mannheim, Germany

In ASL, the inflow of labeled blood is usually modeled by assuming a single arrival time of the bolus in the voxel under consideration. However, it was shown that models, which assume a distribution of arrival times can fit some signal curves more accurately. The goal of this work is to show how a labeled blood bolus is dispersed while traveling down the arterial tree. A short bolus of 500ms length is used and sampled with 100ms temporal resolution. The broadening of this bolus is approximately proportional to the bolus arrival time. This tool might be a sensitive marker to detect local changes of hemodynamics.

                  1514.     Benefits of Short Bolus ASL

Matthias Günther¹

¹Neurology department, University Hospital Mannheim, University Heidelberg, Mannheim, Germany

Usually, a long labeled blood bolus is used in arterial spin labeling (ASL) to yield optimal signal-to-noise ratios in perfusion-weighted images. In this work, properties of short bolus ASL is examined and demonstrated. Benefits of this approach include the approximate measurement of the tissue response curve and the precise probing of properties of parts of the arterial tree. Based on the ASL data with a short bolus length BL data sets can be reconstructed with a virtual bolus length, which is a multiple of BL. This allows calculating ASL time series with a bolus length of e.g. 2500ms, which usually cannot be measured in reality. The deviation between true and calculated bolus is less than 1% for common parameters. Short bolus ASL might probe sensitive to changes due to neuro-degenerative or small vessel disease.

                  1515.     Theoretical and Experimental Comparison of Different Techniques for Continuous Arterial Spin Labelling

Rolf Pohmann¹, Juliane Budde¹, Edward Auerbach², Gregor Adriany², Kamil Ugurbil²

¹Magnetic Resonance Center, Max-Planck-Institute for Biological Cybernetics, Tübingen, Germany; ²Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, USA

Several sequences for continuous arterial spin labelling have been proposed to overcome the technical and conceptual difficulties of this technique. Four different schemes for performing tag and control scans have been simulated for parameter optimization and implemented on a 3 T scanner. All sequences produced excellent perfusion images and were clearly superior to pulsed arterial spin labelling. Both simulations and experiments showed minor differences in SNR between the four techniques.

                  1516.     ASL Optimization for Hippocampus Physostigmine Challenge Perfusion Study

Xiufeng Li¹, Subhendra Sarkar², David M. Buhner³, Robert W. Haley⁴, Richard W. Briggs^3,5

¹Biomedical Engineering, UT Southwestern Medical Center, Dallas, TX, USA; ²Radiology, Beth Israel Deaconess Medical Center, Boston, MA, USA; ³Internal Medicine, UT Southwestern Medical Center, Dallas, TX, USA; ⁴Internal Medicine, UT Southwestern Medical Center , Dallas, TX, USA; ⁵Radiology, UT Southwestern Medical Center, Dallas, TX, USA

To better facilitate hippocampus physostigmine challenge perfusion studies using ASL technique, one optimization study was performed to determine proper post-bolus delay time by performing multiple inversion perfusion studies with fixed labeling time but varied post-bolus delay times for sessions with both saline infusion and PHY infusion. The study results indicate that post-bolus delay times equal to 1.0 s or 1.2 s give lower inter-subject variability of hippocampus CBF measurements for perfusion studies with both saline and PHY challenge. Hippocampus CBF measurements at post-bolus delay equal to 1.2 s showed the largest decrease in CBF with PHY infusion.

                  1517.     Modulated Dual Saturation Pulse Trains for FAIR Studies of Cerebellum Perfusion

Xiufeng Li¹, Subhendra Sarkar², Robert W. Haley³, Richard W. Briggs^3,4

¹Biomedical Engineering, UT Southwestern Medical Center, Dallas, TX, USA; ²Radiology, Beth Israel Deaconess Medical Center, Boston, MA, USA; ³Internal Medicine, UT Southwestern Medical Center, Dallas, TX, USA; ⁴Radiolody, UT Southwestern Medical Center, Dallas, TX, USA

When FAIR with Q2TIPS is applied for perfusion studies of specific brain regions, such as cerebellum, the superior labeled venous blood generates huge undesired artifacts, making CBF estimation in neighboring tissue unreliable. To avoid these adverse artifacts in cerebellum perfusion studies, a modulated dual saturation pulse trains for FAIR (MDS FAIR) technique was implemented and evaluated by performing perfusion studies in the cerebellum. The study results show that the MDS FAIR can greatly minimize these adverse venous artifacts. This technique should also be valuable for perfusion studies of other organs and tissues where similar problems exist.

                  1518.     Correcting for Off-Resonance Induced Degradation of Inversion Efficiency in Pseudo-Continuous ASL

Hesamoddin Jahanian^1,2, Luis Hernandez-Garcia^1,2, Douglas C. Noll^1,2

¹Functional MRI Laboratory, University of Michigan, Ann Arbor, MI, USA; ²Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA

Pseudo-continuous arterial spin labeing (pCASL) uses a long train of labeling pulses to provide multi-slice cerebral perfusion measurements while compensating for magnetization transfer effects without using additional hardware. Changes in local resonance frequency and field gradients, due to field inhomogenities, can compromise the tagging efficiency of pCASL, which causes loss in SNR and can lead to quantification error. Here we examine the efficacy of dynamically changing the residual gradient moment (h) to systematically compensate the unwanted changes in φ thus restoring the tagging efficiency of PCASL. The method is demonstrated using numerical simulation and In-vitro data.

                  1519.     Off-Resonant Artifact Correction of RF Pulse Concatenation for Blood Flow Imaging Applications

Cheng Ouyang¹, Luis Hernandez², Brad P. Sutton^1,3

¹Bioengineering, University of Illinois at Urbana-Champaign, Urbana, IL, USA; ²FMRI Laboratory, University of Michigan, Ann Arbor, MI, USA; ³Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, IL, USA

Concatenation of RF pulses holds great potential for allowing tag and saturation pulses to occur near imaging slices in arterial spin labeling scans or other blood flow imaging methods. However, concatenated RF pulses suffer from reduction of tag efficiency and improper control images when magnetic field inhomogeneity is present. In this abstract, we present a framework for correcting field inhomogeneity effects on the net flip angle of concatenated RF pulses. This framework will allow for future developments of blood flow imaging methods with saturation planes very close to or coincident with the imaging slices.

                  1520.     Continuous Arterial Spin Labeling at 9.4T: How Long to Label?

Hanbing Lu¹, William Rea¹, Elliot A. Stein¹, Yihong Yang¹

¹National Institute on Drug Abuse, National Institutes of Health, Baltimore, MD, USA

A ¡°steady-state¡± condition has often been assumed in ASL quantification. However, when T1 values are remarkably increased at high fields, such as 9.4T, the steady-state condition may not be satisfied when the tagging duration is not sufficiently long. Two practical questions arise: 1) how long should the tagging duration be for reaching a steady-state at 9.4T; and 2) how much error could be potentially introdcued when such assumption is not satisfied. Theoretical analysis and eperimental data are presented. Results show that at 9.4T, short tagging duration (¡Ü4.8s) does not satisfy the ¡°steady-state¡± assumption, systematically underestimating resting-state perfusion values by ~30%. A correction procedure may be required.

                  1521.     Regional White Matter Perfusion Measurement Using an Optimized Pseudo-Continuous ASL MRI

Kun Lu¹, Thomas T. Liu¹, Eric C. Wong¹, Youngkyoo Jung¹

¹Radiology, University of California San Diego, La Jolla, CA, USA

Measuring white matter perfusion using arterial spin labeling (ASL) MRI is challenging due to low SNR, partial volume and transit time effects. In this study we used an optimized pseudo-continuous ASL method to measure transit time and perfusion in major white matter regions across the brain. The optimized method offered significantly improved SNR compared to conventional pulsed and continuous ASL methods and enabled perfusion measurement in white matter. The partial volume effects were reduced by carefully selecting only regions of interest containing more than 90% of white matter. Our results indicated a wide spread of the white matter transit time and perfusion values. The mean transit time for whole brain white matter was 1394 msec and mean perfusion 23.6 ml/100g/min.

                  1522.     Optimization of the Encoding Scheme for Improved SNR Efficiency in Vessel Encoded Pseudo-Continuous ASL

Jia Guo¹, Eric C. Wong²

¹Bioengineering, UC San Diego, La Jolla, CA, USA; ²Radiology and Psychiatry, UC San Diego, La Jolla, CA, USA

In Vessel-Encoded Pseudo-Continuous ASL, encoding schemes with high SNR efficiency are important to correctly decode the vascular territory information. Hadamard type encoding is optimal, but it is not always obvious how to construct such a matrix. In this study, the tagging profile of VE-PCASL is measured from in vivo data, and fitted to a simple model. Based on this model, an encoding scheme with a small number of encoding steps to optimize the efficiency is achieved by configuring the encoding gradients such that the encoding matrix has columns from a Hadamard matrix under constrains such as gradient amplitude.

                  1523.     A Method for Automatic Selection of the Labeling Slabs in Regional Arterial Spin Labeling

Ina Kompan¹, Matthias Günther^1,2, Johannes Heitz³

¹University of Heidelberg, Heidelberg, Germany; ²Universitätsklinikum Mannheim, Mannheim, Germany; ³mediri GmbH, Heidelberg, Germany

The method of regional arterial spin labeling allows to measure the cerebral perfusion of single feeding arteries. Selective positioning of the labeling slabs on the arteries of interest therefore must be accomplished. Manual selection of the slabs is operator-dependent. Here, a method is presented for automatic finding and positioning of the inversion slabs.

                  1524.     Reproducibility of Flow Territories Defined by Plannings-Free Vessel Encoded Pseudo-Continuous Arterial Spin Labeling

Sanna Gevers¹, Aart J. Nederveen¹, Reinoud P.H. Bokkers², Jeroen Hendrikse², Dennis A. Kies³, Wouter M. Teeuwisse³, C.B. Majoie¹, Matthias J.P. van Osch³

¹Radiology, Academic Medical Center, Amsterdam, Noord Holland, Netherlands; ²Radiology, University Medical Center , Utrecht, Netherlands; ³Radiology, Leiden University Medical Center, Leiden, Netherlands

Plannings-free selective arterial spin labeling MRI has the unique capacity to show the perfusion territories of brain feeding arteries non-invasively. The clinical applicability of this method is highly dependent on reliability and accuracy with which different flow territories can be identified. Therefore the aim of the present study was to determine whether RPI based flow territories are imaged sufficiently reliable and accurate to be used in a clinical setting.

                  1525.     Within and Between Session Reproducibility of MR Perfusion Using PICORE Q2TIPS at 3T

Yang Wang¹, Andrew J. Saykin¹, Chen Lin¹, Kristine M. Mosier¹, Andrew J. Kalnin¹, Josef Pfeuffer²

¹IU center for Neuroimaging, Department of Radiology, Indiana University School of Medicine, Indianapolis, IN, USA; ²Siemens Medical Solutions USA, Inc.

In this study, we evaluate within and between session reproducibility of perfusion MR using PASL sequence PICORE Q2TIPS, and compare results with and without physiological noise correction.

                  1526.     Double Acquisition Background Suppressed  (DABS) FAIR at 3T and 7T: Advantages for Simultaneous BOLD and CBF Acquisition.

Roman Wesolowski¹, Penny A. Gowland¹, Susan T. Francis¹

¹School of Physics and Astronomy, University of Nottingham, Sir Peter Mansfield Magnetic Resonance Centre, Nottingham, Nottinghamshire, UK

We have developed and optimised a Double Acquisition Background Suppression (DABS) method for simultaneous CBF and BOLD image collection using FAIR at 3 and 7T. Background suppression reduces physiological noise in ASL by acquiring images close to the null point, but this prohibits simultaneous BOLD acquisition. DABS is a new method which acquires a second BOLD weighted acquisition at the end of each TR period. We have used this technique to obtain qualitative maps of CBF and BOLD haemodynamic responses to a finger tapping task at both 3 and 7T. This technique improves the detection of CBF changes whilst retaining good BOLD contrast.

                  1527.     Background Suppression in Multi Slice Arterial Spin Labeling

Wouter M. Teeuwisse^1,2, Maarten J. Versluis^1,2, Mark A. van Buchem^1,2, Matthias J.P. van Osch^1,2

¹Radiology, Leiden University Medical Center, Leiden, Netherlands; ²C.J.Gorter Center for High Field MRI, Leiden, Netherlands

In Arterial Spin Labeling, background suppression (BS) is known to enable a two fold increase in SNR of the perfusion images. However, for multi slice acquisition BS is only optimal for the first slice and will deteriorate in later slices due to regrowth of the background signal. In this study, efficiency of BS and its relation to SNR is investigated and also, whether addition of BS inversion pulses that are played between acquisition of slices improves BS and SNR for later slices.