Jennifer Campbell¹, Parya MamayyezSiahkal², Peter Savadjiev³, Ilana R. Leppert¹, Kaleem Siddiqi², and G. B. Pike^1
1McConnell Brain Imaging Centre, Montreal Neurological Institute, McGill University, Montreal, Quebec, Canada, ²Centre for Intelligent Machines, McGill University,³Brigham and Women's Hospital, Harvard University

The objective of the current work was to develop an improved probabilistic tractography framework that could handle, in addition to crossing fibres, information on more complex subvoxel geometries, such as fanning fibres. The technique incorporates a residual bootstrap probabilistic processing step, followed by a tractography process that results in the assignment of an index of connectivity, at each voxel in the volume, to the region of interest of the user's choice. This connectivity index is derived using a weakest link approach, and solves many of the problems inherent in popular connectivity indices that are based on frequency of connection.

Stefan Lienhard¹, James Malcolm², Carl-Frederik Westin³, and Yogesh Rathi^2
1Information Technology and Electrical Engineering, ETH Zürich, Zürich, Switzerland, ²Harvard Medical School, Psychiatry Neuroimaging Laboratory, Boston, MA, United States, ³Harvard Medical School, Laboratory of Mathematics in Imaging, Boston, MA, United States

We introduce a tractography method by extending an existing framework which models the signal with Gaussian tensors. At each fiber point an unscented Kalman filter finds the most consistent direction as a mixture of previous estimates and of the local model. In the existing framework the diffusion tensor’s second and third eigenvalues are identical. We extend the tensor representation so that the diffusion tensor can be an arbitrary ellipsoid. Synthetic experiments show better angular resolution at fiber crossings. Tests on in vivo data show that our new model finds fibers in areas where the simpler model stops.

Robert Stefan Vorburger¹, Carolin Reischauer¹, and Peter Boesiger^1
1Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland

High angular resolution diffusion-weighted imaging techniques have been developed to resolve complex intravoxel fiber structure. Until now, just a few dedicated algorithms have been introduced. The current work presents a novel tracking approach that simulates particle motion in a force field which is derived directly from the so-called orientation distribution function using principles of classical mechanics. On the basis of the derived particle tracts, connectivity maps and virtual fibers are subsequently generated. The benefit of the algorithm is demonstrated by presenting tracking results in a healthy volunteer.

Kenji Ito¹, Yoshitaka Masutani^1,2, Yuichi Suzuki², Shigeki Aoki³, Osamu Abe⁴, Akira Kunimatsu^1,2, and Kuni Ohtomo^1,2
1Graduate School of Medicine Univ. of Tokyo, Bunkyo-ku, Tokyo, Japan, ²Univ. of Tokyo Hospital, Bunkyo-ku, Tokyo, Japan, ³Radiology, Juntendo Hospital, Bunkyo-ku, Tokyo, Japan, ⁴Radiology, Nihon University Itabashi Hospital, Itabashi-ku, Tokyo, Japan

Although HARDI (High Angular Resolution Diffusion Imaging) acquisition techinique is essential for crossing fibers analysis, its limitation for clinical situation is the long scan time. We propose a clinically feasible scheme; local-HYDI (Hybrid Diffusion Imaing), which combines whole brain imaging using LARDI (Low Angular Resolution Diffusion Imaging) and local brain imaging with HARDI for crossing fibers volume. Using the local-HYDI data, we also present a Hybrid Tractography (HT) technique based on local switching of deterministic and probabilistic techniques according to data type (LARDI or HARDI) of the location. In this abstract, we evaluated the feasibility of our local-HYDI and HT.

Hsiao-Chin Cheng¹, Yung-Chin Hsu², and Wen-Yih Isaac Tseng^1,3
1Center for Optoelectronic Biomedicine, National Taiwan University College of Medicine, Taipei, Taiwan, ²Department of Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsinchu, Taiwan, ³Department of Medical Imaging, National Taiwan University Hospital, Taipei, Taiwan

We normalized diffusion spectrum imaging data sets, acquired from 7 males and 7 females, to a template using 6D Large Deformation Diffeomorphic Metric Mapping (LDDMM) algorithm. Voxel-based analysis was performed to compute the gender difference in tract volume of the corpus callosum. The males¡¦ tract volume was generally larger than the females¡¦, but there was a spatial variation in the difference. The most prominent difference was found in frontal and temporal lobes, whereas little difference was found in parietal and occipital lobes. Our study demonstrates the feasibility of 6D LDDMM in the analysis of tract volume using voxel-based morphometric approach.

Esmail Davoodi-Bojd¹, Mohammadreza Nazem-Zadeh², Hamid Soltanian-Zadeh¹, and Quan Jiang^2
1Control and Intelligent Processing Center of Excellence, School of Electrical and Computer Engineering, University of Tehran, Tehran, Iran, ²Neurology, Henry Ford Hospital, Detroit, MI, United States

Position Orientation Space (POS) is composed of three dimensions for position and two dimensions for orientation information in each voxel. The POS can be very helpful in low resolution datasets. If two fiber tracts are irresolvable sharing crossing area in three dimensional space, they may be resolvable in five dimensional POS. Since four distinct peaks of the Orientation Distribution Function (ODF) are adequate for extracting the fibers, we propose a novel strategy to the compute major directions from the ODF, then they are employed for segmenting fiber bundles by an algorithm similar to that of Hagmann et al.

Christia Ros¹, Daniel Güllmar¹, and Jürgen R Reichenbach^1
1Medical Physics Group, Department of Diagnostic and Interventional Radiology I, Jena University Hospital, Jena, Thuringia, Germany

To cope with large tractography data sets, we propose COMET – a new framework that is capable to perform autonomous, high quality Cluster analysis Of Major Equivalent Tracts (COMET). The framework facilitates exploratory data analysis of fiber tracts and enables the exploration of axonal pathways and connections, as well as quantitative analysis in large groups of subjects. By exploiting the capabilities of modern multiprocessor system and using new clustering techniques as well as a variety of similarity measures, our toolkit is able to cluster large data sets on the order of minutes.

Mohammadreza Nazem-Zadeh¹, Kourosh Jafari-Khouzani², Abbas Babajani-Fermi², Siamak Pourabdollah Nejad-Davarani¹, Hamid Soltanian-Zadeh^2,3, and Quan Jiang^1
1Neurology, Henry Ford Hospital, Detroit, MI, United States, ²Diagnostic Radiology, Henry Ford Hospital, Detroit, MI, United States, ³Control and Intelligent Processing Center of Excellence, School of Electrical and Computer Engineering, University of Tehran, Tehran, Iran

Using High angular resolution diffusion imaging (HARDI), the fiber orientation distribution function (ODF) on the unit sphere is calculated and used to extract the principal diffusion directions (PDDs). Fast and accurate estimation of PDDs is a prerequisite for tracking algorithms that deal with fiber crossings. In this paper, a clustering approach to estimate PDDs is proposed which is an extension of fuzzy c-means clustering developed for orientation coordinates of points on a sphere. Experimental results illustrate that the proposed clustering algorithm is more accurate, more resistant to noise, and faster than the techniques currently being utilized.

Pew-Thian Yap¹, John H. Gilmore², Weili Lin¹, and Dinggang Shen^1
1Radiology and BRIC, University of North Carolina, Chapel Hill, NC, United States, ²Psychiatry, University of North Carolina, Chapel Hill, NC, United States

Tractography in an atlas space allow the reconstructed trajectories to form a common geometry onto which diffusion properties from the individual images can be projected for tract-based comparison. We show, however, that conventional average-atlas-based approach, when applied to HARDI data, causes significant deviation of the estimated local orientations from the 'true' orientations, inevitably jeopardizing subsequent trajectory reconstruction. In our approach, local fiber orientation information is estimated by harnessing orientation information simultaneously from all images in a population. We model the orientation statistics at each voxel location by employing the bipolar Watson distribution, which will capture the mean orientations of the fiber bundles and also the related degrees of orientation dispersion. This distribution information, when fed into a stochastic tractography algorithm allows reconstruction of fiber trajectories which are consistent across images in the population.

Laura Mancini^1,2, Faiza Javad², Jason D Warren³, John S Thornton^1,2, Xavier Golay^1,2, Tarek Yousry^1,2, and Caroline Micallef^1,2
1Lysholm Dept of Neuroradiology, National Hospital for Neurology and Neurosurgery, UCLH NHS Foundation Trust, London, WC1N 3BG, United Kingdom, ²Academic Neuroradiological Unit, Dept Brain Repair and Rehabilitation, UCL Institute of Neurology, London, WC1N 3BG, United Kingdom, ³Dementia Research Centre, UCL Institute of Neurology, London, WC1N 3BG, United Kingdom

This is the first combined DTI/fMRI study to investigate pathways connecting cortical and sub-cortical structures in the auditory system. Auditory pathways connect the inferior collicular nucleus (ICN) and medial geniculate body (MGB) to the auditory cortex. These tracts are particularly difficult to identify because they intersect the optic radiation and numerous other fascicles. 2.3mm isotropic DTI (64 gradient directions, b-value=1400s/mm ²) were analyzed with probabilistic, 2-tensor model tractography. ICN and MGB were identified anatomically, while auditory cortices were identified by fMRI using sparse acquisition and amplitude-modulated iterated-ripple-noise pitch as stimuli. Our results successfully identified sub-cortical auditory projections in 14 healthy subjects.

Michel Thiebaut de Schotten^1,2, Flavio Dell'Acqua^1,3, Stephanie Forkel^1,4, and Marco Catani^1,3
1Natbrainlab, Institute of Psychiatry, London, United Kingdom, ²Hopital de la Salpêtrière, CRICM-INSERM UMRS 975, Paris, France, ³Department of Neuroimaging Sciences, Institute of Psychiatry, London, United Kingdom, ⁴Department of Forensic and Neurodevelopmental Sciences, Institute of Psychiatry, London, United Kingdom

Little is known about how the size of tract can modify the speed of conduction. Larger tract volumes could depend on a number of factors, including greater fibre myelination, higher number of axons and larger axonal diameter. Experimental physiology has shown that the conduction speed of larger diameter, or more myelinated axons is faster. A higher number of axons would also boost the speed of conduction by assuring a parallel processing. So, are larger pathways faster ? In this study we found a direct correlation between tract volume and the speed of detection visual events.

Kerstin Pannek¹, Thomas Kampf², Jane Mathias³, Greg Brown⁴, Jamie Taylor⁵, Olivier Salvado⁶, and Stephen Rose^7
1Centre for Advanced Imaging, The University of Queensland, Brisbane, Queensland, Australia, ²Department of Experimental Physics 5, University of Wuerzburg, Wuerzburg, Germany, ³School of Psychology, University of Adelaide, Adelaide, South Australia, Australia, ⁴MRI Unit, Royal Adelaide Hospital, Adelaide, South Australia, Australia, ⁵Radiology, Royal Adelaide Hospital, Adelaide, South Australia, Australia, ⁶Biomedical Imaging, Australian eHealth Research Centre, Brisbane, Queensland, Australia, ⁷Centre for Clinical Research, The University of Queensland, Brisbane, Queensland, Australia

Streamline number and streamline length are quantitative tractography metrics that are influenced by white matter pathology. We propose to assess streamline length in a fully automated voxel-wise manner. The length distribution within an individual voxel can be described by a mixture of Gaussian distributions, and compared across subjects. Voxel-wise length distributions appear to be highly reproducible over time. We demonstrate how this new method can be used to identify fibre populations affected by white matter pathology.

Firat Kara¹, Fu Chen¹, Jörg Matysik¹, and Alia Alia^1
1Leiden Institute of Chemistry, Leiden University, Leiden, South holland, Netherlands

Knowledge of T₂ relaxation times for mouse brain at ultra high field (17.6 T) can be important to optimize imaging parameters for optimum contrast to noise and higher sensitivity and to observe changes induced by various pathological conditions. In this work in vivo T₂ relaxation parameters for mouse brain have been measured at 17.6 T and compared with those measurements at 9.4 T. Phantom solutions were used to quantify and validate changes in T₂ relaxation time at different field strengths. A decrease in T₂ relaxation time was found in several regions of mouse brain at 17.6 T as compared with 9.4 T. Phantom results validated a decrease in T₂ relaxation time at higher field strengths.

Nyoman Dana Kurniawan¹, Gary Cowin¹, Shaun P. Collin^2,3, and Jeremy F.P. Ullmann^3
1Centre for Advanced Imaging, The University of Queensland, Brisbane, Queensland, Australia, ²School of Animal Biology, The University of Western Australia, Crawley, Western Australia, Australia, ³School of Biomedical Sciences, The University of Queensland, Brisbane, Queensland, Australia

Zebrafish is an important model in development and neuroscience research. However due to its extremely small size (4x2x1mm), ultra-high resolution MR diffusion images are required to obtain meaningful information. Here we present the white matter tracks of the zebrafish brain reconstructed using Track Density Imaging at 5-micron resolution and comparison with conventional high-resolution anatomical MRI.

Yulin V Chang¹, and Philip V Bayly^1
1Mechanical Engineering, Washington University, St. Louis, MO, United States

We investigated the relationships between cortical folding, T₂, average ADC, and diffusion anisotropy in a developing ferret brain using diffusion tensor imaging. Our results show that brain folding is accompanied by the vanishing of the diffusion anisotropy in the gray matter. We observed that the white matter has not been fully myelinated by the last time point (P30) of measurement, which suggests that cortical folding and white matter myelination are independent processes during brain development.

Lesley M Foley¹, T Kevin Hitchens^1,2, John A Melick³, Nancy T Ho², Tusey C Tam², Chien Ho^1,2, and Patrick M Kochanek^3,4
1Pittsburgh NMR Center for Biomedical Research, Carnegie Mellon University, Pittsburgh, PA, United States, ²Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA, United States, ³Safar Center for Resuscitation Research, University of Pittsburgh School of Medicine, Pittsburgh, PA, United States, ⁴Departments of Critical Care Medicine, Pediatrics and Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, PA, United States

Using MRI we assessed brain and pulmonary edema and cerebral blood flow (CBF) after resuscitation, from TBI+HS using two conventional solutions, namely the crystalloid Lactated Ringers (LR), the colloid hextend (Hex), and an octomeric recombinant hemoglobin (rHb). MRI assessment of edema using 1/T1 seemed to provide a more sensitive measurement than wet weight/dry weight values. Recombinant hemoglobin whilst increasing CBF initially also produces slightly more edema than either LR or Hex. One possibility is that rapid restoration of CBF in the damaged brain with rHb results in perfusion of severely damage tissue and edema.

Qi Peng^1,2, Yi Zhang^1,2, Oscar San Emeterio Nateras^1,2, and Timothy Q Duong^1,2
1Radiology, UT Health Science Center at San Antonio, San Antonio, TX, United States, ²Research Imaging Institute, UT Health Science Center at San Antonio, San Antonio, TX, United States

Blood flow (BF) measurement of the human retina is challenging because the thin retina is located in a region of high magnetic susceptibility, is susceptible to eye motion and requires high spatial resolution. This study successfully demonstrated the feasibility of high spatial-resolution (500x800¦Ìm) retinal BF measurement under baseline and hypercapnia. Pseudo-continuous arterial spin-labeling technique with background suppression and single-shot turbo spin-echo acquisition were employed to improve BF sensitivity, suppress vitreous signal, and achieve high spatial resolution free of image distortion and signal dropout. This approach could open up new avenues for retinal research and may have important clinical applications.

Yi Zhang¹, Oscar San Emeterio Nateras², Qi Peng^1,2, Carlos A. Rosende³, John M. Johnson⁴, and Timothy Q. Duong^1,2
1Research Imaging Institute, University of Texas Health Science Center at San Antonio, San Antonio, TX, United States, ²Radiology, University of Texas Health Science Center at San Antonio, San Antonio, TX, United States, ³Ophthalmology, University of Texas Health Science Center at San Antonio, San Antonio, TX, United States,⁴Physiology, University of Texas Health Science Center at San Antonio, San Antonio, TX, United States

This study investigated the relation between perfusion pressure and blood flow (BF) in the human retina using MRI during rest and isometric exercise (squeezing a tennis ball inside the MRI scanner). Basal BF in the posterior retina was 137±47mL/100mL/min (±SD, N=4). Isometric exercise increased mean BF, heart rate, mean arterial pressure, and ocular perfusion pressure (P<0.05), but not intraocular pressure, arterial oxygen saturation, end-tidal carbon dioxide, or respiratory rate (P>0.1). A MRI approach provides objective quantitative BF with a large field of view without depth limitation. BF MRI during isometric exercise provides a unique means to study retinal physiology and autoregulation free of adverse pharmacological effects.

Guang Li¹, Bryan De La Garza², Yen-Yu I Shih², Eric R Muir^2,3, and Timothy Q Duong^2
1Radiology, UT Health Science Center at San Antonio, San Antonio, Texas, United States, ²UT Health Science Center at San Antonio, United States, ³Georgia Institute of Technology, Atlanta, Georgia, United States

Vision loss due to retinal degeneration is a major problem in ophthalmology. We developed blood flow (BF) MRI (44x44x600 μm³) using continuous arterial spin labeling at 11.7T to image layer-specific, quantitative retinal BF (RBF) and choroidal BF (ChBF) in the rat eye. This method was used to investigate BF changes in an animal model of progressive retinal degeneration, the Royal-College-of-Surgeons (RCS) rat. In this model, RBF and ChBF were affected differently by retinal degeneration. RBF was attenuated in RCS rats as the retina degenerated, while ChBF likely was not. BF MRI provides layer-specific quantitative BF data of the retina without depth limitation and with a large field-of-view, potentially opening up new avenues for retinal disease research in animal models.

Eric R Muir¹, William Lavery², Jeffrey W Kiel², René C Rentería^3,4, and Timothy Q Duong^1
1Research Imaging Institute, University of Texas Health Science Center, San Antonio, TX, United States, ²Department of Ophthalmology, University of Texas Health Science Center, San Antonio, TX, United States, ³Department of Physiology, University of Texas Health Science Center, San Antonio, TX, United States, ⁴Center for Biomedical Neuroscience, University of Texas Health Science Center, San Antonio, TX, United States

Glaucoma, a leading cause of blindness worldwide, is characterized by progressive degeneration of retinal ganglion cells and the optic nerve. Elevated intraocular pressure, which is associated with glaucoma, may reduce blood flow (BF) in the eye. The retina is nourished by two separate vasculatures, the retinal and choroidal vessels. Arterial spin labeling MRI was used to image layer-specific retinal and choroidal BF in the DBA/2J mouse model of glaucoma at different stages of disease. Retinal and choroidal BF were distinctively reduced at different ages in DBA/2J mice. MRI provided a non-invasive method to monitor vascular changes in rodents in vivo.

Andrea Federspiel¹, Ariane Orosz¹, Martinus Hauf², Roland Wiest², Danny JJ Wang³, Thomas Dierks¹, and Kay Jann^1
1Department of Psychiatric Neurophysiology, University Hospital of Psychiatry, Bern, Switzerland, ²Institute of Diagnostic and Interventional Neuroradiology, University of Bern, Switzerland, ³Department of Neurology, UCLA, Ahmanson-Lovelace Brain Mapping Center, Los Angeles, CA, United States

Calibrated fMRI is performed with simultaneous EEG and fMRI recording. In the fMRI setting a set of ASL and BOLD images are acquired with hypercapnia condition and a set of ASL and BOLD images during visual stimulation (checkerboard 2Hz). Calculation of CMRO2 during hypercapnia was performed and revealed values in line with previous findings. Visual evoked potentials showed latency of P100 peak at 116 ms. During hypercapnia a reduced power in frequency bands theta and alpha 2 are observed. These findings suggest that during hypercania CMRO2 may not be constant. These findings may have implication in future calibrated fMRI setting.

Lars Michels¹, Ernst Martin¹, Daniel Brandeis², Rafael Lüchinger², Peter Klaver³, Ajit Shankaranarayanan⁴, David C Alsop^5,6, and Ruth L O'Gorman^1
1University Children's Hospital, Zürich, Switzerland, ²Department of Child and Adolescent Psychiatry, University of Zürich, Zürich, Switzerland, ³Department of Psychology, University of Zürich, Zürich, Switzerland, ⁴Global Applied Science Laboratory, GE Healthcare, Menlo Park, CA, United States, ⁵Beth Israel Deaconess Medical Center, Boston, MA, United States, ⁶Harvard Medical School, Boston, MA, United States

This study examines the relationship between resting EEG power fluctuations in low, medium, and high frequency bands and resting cerebral perfusion. EEG and ASL data were acquired in separate measurement sessions in a group of 12 healthy adults. Peak EEG power correlated positively with perfusion in a widespread network including both cortical and sub-cortical regions. After controlling for whole-brain ASL perfusion, significant correlations were restricted to a smaller network of regions, and predominantly negative correlations were found for alpha frequencies, whereas higher frequencies (gamma) exhibited predominantly positive correlations.

Inês Sousa^1,2, Pedro Vilela³, and Patricia Figueiredo^1
1Institute for Systems and Robotics, Instituto Superior Técnico, Lisbon, Portugal, ²Healthcare Sector, Siemens, S.A., Lisbon, Portugal, ³Imaging Department, Hospital da Luz, Lisbon, Portugal

An approach for the optimization of a Gamma impulse response function to be used in a GLM analysis ASL perfusion and BOLD data, collected during a Cued Deep Breathing paradigm, is proposed. The optimal parameter values of the Gamma function were determined, for the whole-brain in terms of maximum number of active voxels, and on a voxel-by-voxel basis in terms of the maximum Z score. The results obtained indicate that a voxe-by-voxel optimization may be preferable due to the spatial heterogeneity of the parameters, yielding optimal lag and width maps and contributing to more sensitive and accurate cerebrovascular reactivity measurements.

Chun-Xia Li¹, Sudeep Patel¹, Eddie Auerbach², and Xiaodong Zhang^1
1Yerkes Imaging Center, Yerkes National Primate Research Center, Emory University, Atlanta, GA, United States, ²Center for MR Research, School of Medicine, University of Minnesota, Minneapolis, United States

Non-human primates were widely used as various disease models and examined under isoflurane anesthesia.Isoflurane is believed to increase the cerebral blood flow in general but the detailed effects in the monkey brain still remain unknown. In this study, the dosage effects of isoflurane (0.6 to 1.2 MAC) on CBF in the different brain regions of monkey brain were investigated with the continuous arterial-spin-labeling (CASL) technique.

Siyuan Hu¹, Hengyi Rao¹, Lauren Mancuso¹, John A. Detre¹, and David Wolk^1
1Department of Neurology, University of Pennsylvania, Philadelphia, PA, United States

The medial temporal lobe (MTL) plays a critical role in episodic memory function, and is activated by episodic memory tasks. Deficits in episodic memory performance are also seen in aging and in Alzheimer's disease. Here we correlated resting MTL function as measured by arterial spin labeled (ASL) perfusion MRI with episodic memory performance in 31 cognitively normal elderly participants. After controlling for age, years of education, gender, and global CBF values, we found a negative correlation between episodic memory performances and resting CBF in left hippocampus. These findings suggest that resting MTL perfusion provides a biomarker of memory performance phenotype, and that increased CBF may represent a compensatory response to memory decline.

Guangming Lu¹, Zhiqiang Zhang¹, Cuiping Yuan¹, and Lianfang Shen^1
1Department of Radiology, Jinling hospital, Nanjing University School of Medicine, Nanjing, Jiangsu, China, People's Republic of

Interictal single-photon emission computed tomography (SPECT) studies have demonstrated that there is hypoperfusion within the extra-temporal structures besides to the temporal lobe in mesial temporal lobe epilepsy (mTLE), which contributes to the proposal of concept of the mesial temporal lobe epilepsy network [1]. The purpose of this study was to determine the feasibility of detecting perfusion abnormalities in mTLE using arterial spin labeling (ASL)-based MRI, which is a noninvasive method for calculating regional cerebral blood flow (rCBF).

Abhishek Yadav¹, Rakesh Kumar Gupta¹, Santosh Kumar Yadav¹, M Rangan², V A Saraswat³, M A Thomas⁴, and R KS Rathore^5
1Radiodiagnosis, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Lucknow, India, Lucknow, Uttar Pradesh, India, ²Pediatric Gastroenterology, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Lucknow, India, Lucknow, UP, India, ³Pediatric Gastroenterology, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Lucknow, India, lucknow, UP, India, ⁴Department of Radiological Sciences, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Lucknow, India, California, Los Angels, United States, ⁵Department of Mathematics & Statistics, Indian Institute of Technology, Kanpur, UP, India

Acute-on-chronic liver (ACLF) failure develops in patients with previously well-compensated chronic liver disease following an acute precipitating event. It is known that the cerebral autoregulation may be defective in patients of liver failure, and raised ICP is often seen in ALF patients. Ammonia and cytokines are known to increase in ACLF, and have synergistic role in pathogenesis of HE. The current data suggest that ASL demonstrates the increase in CBF various grey matter regions in ACLF and may be used in the in initial and follow up study of these ACLF patients.

Brian A Taylor¹, Adam Winchell^1,2, Jan Sedlacik¹, Alberto Broniscer³, Ruitian Song¹, Ralf B Loeffler¹, and Claudia M Hillenbrand^1
1Radiological Sciences, St. Jude Children's Research Hospital, Memphis, TN, United States, ²Biomedical Engineering, University of Memphis, Memphis, TN, United States,³Oncology, St. Jude Children's Research Hospital, Memphis, TN, United States

An algorithm that combines dynamic susceptibility contrast (DSC) and arterial spin labeling (ASL) imaging for quantitative perfusion measurements was evaluated in a large clinical study in children with diffuse pontine glioma. DSC measurements were calibrated to ASL measurement in voxels with low transit times. An alternative method was evaluated which calibrated DSC to ASL in the gray matter.

Alexandre Coimbra¹, Dai Feng², Sonia Apreleva², Peter Hu³, S Ramana⁴, A Bernstein⁵, Matthias Guenther⁶, William Cho⁷, Mark Forman⁸, Ajay Verma⁹, Gary Herman¹⁰, Richard Baumgartner², and David Feinberg^4
1Imaging, Merck & Co, Inc, West Point, PA, United States, ²Biometrics, Merck & Co, Inc, Rahway, NJ, United States, ³BARDS, Merck & Co, Inc, Upper Gwynedd, PA, United States, ⁴Advanced MRI Technologies, Sebastopol, CA, United States, ⁵Redwood Regional Medical Group, Santa Rosa, CA, United States, ⁶Fraunhofer MEVIS-Institute for Medical Image Computing, Bremen, Germany, ⁷Experimental Medicine, Merck & Co, Inc, Upper Gwynedd, PA, United States, ⁸Clinical Pharmacology, Merck & Co, Inc, Upper Gwynedd, PA, United States, ⁹Translational Neurology, Biogen Idec, Cambridge, MA, United States, ¹⁰Clinical Research, Merck & Co, Inc, Rahway, NJ, United States

In this contribution we assessed the test-retest reproducibility of 3D GRASE ASL technique at 1.5 T and in populations of AD patients and age matched control. Assessment of measurement reproducibility was done using graphical methods as well as quantitative metrics such as Intraclass Correlation Coefficient and within subject coefficient of variability. Our findings suggest that the test-retest reproducibility varies between ROIs, and overall moderate to very good reproducibility can be achieved. Assessment of reproducibility is an important first step to inform design (e.g. parallel versus cross-over) of future studies of disease progression and treatment effect.

Xiao Wang¹, Xiao-hong Zhu¹, Yi Zhang¹, and Wei Chen^1
1Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota Medical School, Minneapolis, MN, United States

In the present study, the absolute CBF increase induced by transient mild hypercapnia in the rat brain was directly compared using the SR-T1app method and the CASL technique. The results revealed good agreement in both magnitude and spatial patterns of CBF change measured by these two techniques. In addition, both techniques showed great sensitivity to the variation of hypercapnia level and the associated CBF change. Our results also show that the SR-T1app method could also provide absolute CBF value once the intrinsic R1 (R1int) was determined. Therefore, the SR-T1app method should provide a noninvasive, simple and efficient way to determine both absolute CBF and CBF change induced by physiological and pathological perturbations in the rat brain.

Yufen Chen¹, Hengyi Rao¹, and John A. Detre^1
1Center for Functional Neuroimaging, University of Pennsylvania, Philadelphia, PA, United States

Cerebral blood flow (CBF) is tightly coupled to brain metabolism and is known to be modulated by age and gender. But little is known about intersubject variability in CBF, which may be reflective of individual phenotypic differences. Here, we retrospectively analyzed arterial spin labeling (ASL) data from 136 subjects to test the hypothesis that metabolic variance exceeds structural variance. F-tests showed gray matter (GM) CBF had higher variance than GM volume. Linear model of age and gender showed reduced R² fit to GM CBF compared to GM volume, suggesting the presence of additional sources of variability.

David Dongsuk Shin¹, Burak Ibrahim Ozyurt², and Thomas T Liu^1
1Center for Functional MRI, University of California, San Diego, La Jolla, CA, United States, ²Department of Psychiatry, University of California, San Diego, La Jolla, CA, United States

A rapidly growing number of CBF measures are being collected both in clinical and research settings around the world. Here we present an online CBF database with an integrated analysis pipeline for CBF quantification (CBFDAP). To date, we have successfully processed and accumulated several hundred CBF datasets acquired with FAIR and OptPCASL protocols for a range of subject populations. The number of datasets is expected to grow rapidly as we begin to make the CBFDAP available to the general public. The CBFDAP provides an infrastructure for the easy upload, processing, storage, retrieval, and exploration of ASL-based CBF data.