Dmitry Kurzhunov¹, Robert Borowiak^1,2, Marco Reisert¹, Philipp Wagner¹, Axel Krafft^1,2, and Michael Bock^1
1University Medical Center Freiburg, Dept. of Radiology - Medical Physics, Freiburg, Germany, ²German Cancer Research Center (DKFZ), German Cancer Consortium (DKTK), Heidelberg, Germany

This work presents a comparison analysis of different reconstruction techniques for quantification of 3D maps of the cerebral metabolic rate of oxygen consumption (CMRO₂) in human brain. Several ¹⁷O-MR 3D data sets of a healthy volunteer’s brain were acquired at a clinical 3 Tesla MR system with inhalation of 70%-enriched ¹⁷O₂ gas. Iterative image reconstruction procedures, e.g. where different co-registered ¹H MR image data sets of high spatial resolution act as edge-preserving constraints, are compared and used to improve the image quality and the precision of CMRO₂ mapping. Anisotropic Diffusion as non-Homogeneous Constraint (ADHOC) is shown to be superior.

Tomoki Fujii¹, Krishna R. Singh², Bill Bordeau³, Joao A. Lima¹, and Bharath Ambale-Venkatesh^1
1Johns Hopkins University, Baltimore, MD, United States, ²Prairie Vascular Institute, Springfield, IL, United States, ³Zimmer Biomet Biologics, Warsaw, IN, United States

Peripheral artery disease is a major public health concern particularly among the elderly. Although measures such as ankle-brachial index and segmental pressures have been used to characterize disease severity, MRI techniques allow us to assess subclinical vascular function and morphology and may help improve our understanding of vascular adaptations. In a small pilot study, we test whether hyperemia-induced BOLD oxygenation changes are a viable measure of tissue oxygenation in the foot and if they represent the reduced oxygenation seen in PAD.

Marina Lysenko¹, Noam Ben-Eliezer¹, Inbal E Biton², Joel R Garbow³, and Michal Neeman^1
1Biological Regulation, Weizmann Institute of Science, Rehovot, Israel, ²Veterinary Resources, Weizmann Institute of Science, Rehovot, Israel, ³Biomedical Magnetic Resonance Laboratory, Mallinckrodt Institute of Radiology, Washington University, St. Louis, MO, United States

The murine placenta is a complex organ, consisting of different cell compartments that greatly influence its blood-flow pattern. Dynamic contrast enhanced (DCE) MRI of murine placental perfusion has been reported previously using both low and high MW contrast media. In this study, we used high-MW, albumin-based macromolecular contrast agent that does not cross the placental barrier, but, instead, forms contrast-based aggregates that accumulate in the maternal vasculature simultaneously with active contrast internalization by trophoblast cells in the labyrinth .To interpret the observed data, we suggest a novel model for describing feto-maternal processing and aggregate formation of labeled albumin in placental DCE-MRI experiments.

André Ahlgren¹, Ronnie Wirestam¹, Freddy Ståhlberg^1,2,3, and Linda Knutsson^1
1Department of Medical Radiation Physics, Lund University, Lund, Sweden, ²Department of Diagnostic Radiology, Lund University, Lund, Sweden, ³Lund University Bioimaging Center, Lund University, Lund, Sweden

Partial volume effects (PVE) can significantly affect parameter estimates in perfusion MRI. In contrast to arterial spin labeling (ASL), the impact of PVEs in dynamic susceptibility contrast MRI (DSC-MRI) has not yet been well established. In this work, we assess and compare partial volume correction (PVC) of DSC-MRI and ASL data in 20 healthy subjects. PVC reduced the tissue volume dependence of perfusion estimates in DSC-MRI and ASL. White matter perfusion maps were of higher quality for DSC-MRI. However, for PVC of DSC-MRI we used several assumptions which need further evaluation.

Marco Pizzolato¹, Rutger Fick¹, Timothé Boutelier², and Rachid Deriche^1
1Athena Project-Team, Inria Sophia Antipolis - Méditerranée, Sophia Antipolis, France, ²Olea Medical, La Ciotat, France

Bolus dispersion phenomena affect the residue function computed via deconvolution of DSC-MRI data. Indeed the obtained effective residue function can be expressed as the convolution of the true one with a Vascular Transport Function (VTF) that characterizes the dispersion. The state-of-the-art technique CPI+VTF allows to estimate the actual residue function by assuming a model for the VTF. We propose to perform deconvolution representing the effective residue function with Dispersion-Compliant Bases (DCB) without assumptions on the VTF, and then apply the CPI+VTF on DCB results. We show that DCB improve robustness to noise and allow to better characterize the VTF.

Liyuan Song¹, Lizhi Xie², and Junfang Xian^1
1Department of Radiology,Beijing Tongren Hospital,Capital Medical Universityy, Beijing, China, People's Republic of, ²GE Healthcare, MR Research China, Beijing, Beijing, China, People's Republic of

This work assessed the feasibility of quantitative parameters derived from dynamic contrast enhanced MR imaging (DCE-MRI) and evaluate the value of quantitative dynamic contrast enhanced MR imaging in the diagnosis and differential diagnosis of orbital masses in adults. From the result we can see that it is feasible that quantitative parameters of orbital masses can be derived from DCE-MRI. ROI onf the earliest and most enhanced area was optimal for distinguishing benign masses from malignant masses in orbit.

Jacob M. Johnson¹, Leah C. Henze Bancroft², James H. Holmes³, Edward F. Jackson^1,2, Frank R. Korosec^1,2, Courtney K. Morrison², Roberta M. Strigel¹, Kang Wang³, and Ryan J. Bosca^1
1Radiology, University of Wisconsin, Madison, WI, United States, ²Medical Physics, University of Wisconsin, Madison, WI, United States, ³GE Healthcare, Madison, WI, United States

The recent development of a multi-modality, commercially available, dynamic flow phantom has provided a means of assessing the repeatability, reproducibility, and fidelity of contrast concentration time courses. In this work, we aimed to develop and evaluate a methodology for assessing the repeatability and reproducibility contrast concentration time courses derived from dynamic contrast-enhanced MR images of this dynamic flow phantom.

Irene Klærke Mikkelsen¹, Anna Tietze^1,2, Lars Ribe¹, Anne Obel³, Mikkel Bo Hansen¹, and Kim Mouridsen^1
1CFIN, Aarhus University, Aarhus, Denmark, ²Dept. of Neuroradiology, Aarhus University Hospital, Aarhus, Denmark, ³Neuroradiology, Aarhus University Hospital, Aarhus, Denmark

Dynamic Contrast Enhanced Perfusion Imaging (DCE) allows for quantification of the blood-brain barrier integrity in tumor patients. A key post-processing step is to fit a hemodynamic model to DCE data. The fitting procedure can, however, cause spurious voxels and image degradation. We compared the widely used Levenberg-Marquardt fitting algorithm to a Bayesian algorithm. Image quality was assessed in 42 tumor patients. The Bayesian approach provided the highest image quality scores. This was confirmed in simulated data with fewer outliers (spurious voxels) when using the Bayesian approach. The hemodynamic two-compartment model that separates cerebral blood flow and leakage, provides reliable Ve images, when the robust Bayesian fitting algorithm is used.

Jost Michael Kollmeier¹, Volkert Roeloffs¹, and Jens Frahm^1
1Biomedizinische NMR Forschungs GmbH, Max-Planck-Institut für biophysikalische Chemie, Göttingen, Germany

We present a DCE-MRI experiment using a commercial perfusion flow phantom for quantitative analysis of image series with high spatial and high temporal resolution (107 ms). Both can be obtained by current real-time MRI methods, i.e. radial undersampled radial FLASH and image reconstruction by nonlinear inversion (NLINV). Contrast agent bolus tracking with high CNR and quantitative parameter maps are presented.

Zhe Han^1,2, Juan Chen², Min Chen², Chen Zhang², and Dandan Zheng^3
1Chinese Academy of Medical Science and Peking Union Medical College, Beijing, China, People's Republic of, ²Department of Radiology, Beijing Hospital, Beijing, China, People's Republic of, ³GE Healthcare, MR Research China, Beijing, China, People's Republic of

In this study we compared the association of dynamic contrast-enhanced (DCE)-derived quantitative parameters with the histologic grade, N-stage, epidermal growth factor receptor (EGFR) expression and K-RAS gene mutation of primary rectal cancer.Significant correlations were found between Ktrans values and N-stage, Ktrans values and EGFR expression, Kep values and EGFR expression. DCE-derived quantitative parameters may be a promising imaging biomarker of tumor aggressiveness and prognosis.

SoHyun Han¹ and HyungJoon Cho^1
1Biomedical Engineering, Ulsan National Institute Science and Technology, Ulsan, Korea, Republic of

In vivo estimation of Gd-concentration in dynamic contrast enhanced (DCE)-MRI are often compromised from non-negligible T2* effect and limited temporal resolution. In this study, we introduce compressed sensing assisted turbo spin echo (CS-TSE) acquisition to provide accurate Gd-concentration estimation without the need of additional signal calibration, and to achieve a sub-second temporal resolution with extended slice coverage. Phantom verification followed by in vivo arterial input function (AIF) studies validated the faithful concentration estimation of CS-TSE. Robust measurement of first-pass kidney feeding AIF with increased temporal resolution was demonstrated with sub-second temporal resolution.

Pavan poojar¹, Bikkemane Jayadev Nutandev², Nithin N Vajuvalli¹, C.K. Dharmendra Kuman², Ramesh Venkatesan³, and Sairam Geethanath^1
1Medical Imaging Research Centre, Dayananda Sagar College of Engineering, Bangalore, India, ²Bangalore, India, ³Wipro-GE Healthcare, Bangalore, India

In dynamic scans, the significant values of k-space dependent on the shape of the organ which leads to arbitrary k-space trajectories. Gradient optimization for arbitrary k-space trajectory using active contour is a new acquisition technique that has been applied on six DCE breast data. The arbitrary k-space trajectory was obtained by active contour and gradients are optimized by employing convex optimization based on hardware constraints. Image reconstruction was performed using Fourier transform with density compensation.  $$$K^{trans}$$$ and Ve maps were generated for different acceleration factors (1x, 2x, 3x, 4x and 10x) on tumor region to demonstrate utility of the method.

Nithin N Vajuvalli¹, Shivaprasad Ashok Chikop¹, and Sairam Geethanath^1
1Medical Imaging Research Centre, Dayananda Sagar Institutions, Bangalore, India

This study is of relevance to MR researchers interested in DCE-MRI. Tofts model is a well-established two compartment model to determine the PharmacoKinetic (PK) maps, which is time consuming due to the presence of iterative curve fitting for each voxel. Current work focuses on the application of Partial Least Square (PLS) regression modelling to determine PK maps. PLS is a statistical method based on PCA and linear regression that provides the relationship between the predictor and response variables. We report 95-98% reduction in time as compared to curve fitting approaches for in silico phantoms and in vivo breast DCE data.

Graeme A Keith¹, Christopher T Rodgers¹, Michael A Chappell², and Matthew D Robson^1
1Oxford Centre for Clinical Magnetic Resonance Research, University of Oxford, Oxford, United Kingdom, ²Institute of Biomedical Engineering, University of Oxford, Oxford, United Kingdom

A previously presented arterial spin labelling (ASL) method was tested for reproducibility and variability. These measures are important to consider when planning a clinical study. The results presented show that the method has the sensitivity required to detect changes in MBF in pathology and under stress. The variation in individuals is shown to be less than across the sample as a whole. This knowledge will be useful in the planning of future clinical research studies.

James R Larkin¹, Manon A Simard¹, Alexandre A Khrapitchev¹, Kevin J Ray¹, James A Meakin², Paul Kinchesh¹, Sean Smart¹, Peter Jezzard², Michael A Chappell³, and Nicola R Sibson^1
1CRUK and MRC Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, Oxford, United Kingdom, ²FMRIB Centre, University of Oxford, Oxford, United Kingdom, ³Institute of Biomedical Engineering, Department of Engineering, University of Oxford, Oxford, United Kingdom

Arterial spin labelling perfusion imaging in the rodent brain is easily confounded by off-resonance effects at the tagging plane. These effects are a consequence of the higher field strengths used pre-clinically and the nearby air cavities in the rodent head and neck, something not as problematic in the clinic. By implementing a multiphase pCASL sequence with eight phases spaced at 45° and lying between 0 and 315°, it is possible to obtain data to allow fitting thereby accounting for any off-resonance effects. This process dramatically improves image quality without excessively affecting acquisition time. 

Adam Bush¹, Jon Detterich², Thomas Coates³, Herbert Meiselman⁴, and John Wood^1
1Biomedical Engineering/ Cardiology, University of Southern California/ Children's Hospital Los Angeles, Los Angeles, CA, United States, ²Cardiology, Children's Hospital Los Angeles, Los Angeles, CA, United States,³Hematology, Children's Hospital Los Angeles, Los Angeles, CA, United States, ⁴Physiology and Biophysics, University of Southern California, Keck School of Medicine, Los Angeles, CA, United States

Precise knowledge of the T2 of blood (T2b) is required for spin-echo based blood oxygenation determination methods such as TRUST (T2 Relaxation Under Spin Tagging).  In this study we measure the T2b in vivo and vitro using TRUST MRI.  After correcting for physiologic variable we found that our model of T2b is statistically significantly different from the models used by other groups.  We conclude those model lead to errors in derived parameters including oxygen saturation, oxygen extraction fraction and cerebral metabolic rate.

Marijn van Stralen¹, Esben Thade Petersen^1,2, Jeroen Hendrikse¹, and Clemens Bos^1
1University Medical Center Utrecht, Utrecht, Netherlands, ²Danish Research Center for MR, Hvidovre, Denmark

Abdominal perfusion imaging using contrast media injection is potentially nephrotoxic. Arterial spin labeling (ASL), employing endogenous contrast, was shown using spatially selective labeling strategies. We investigated the reproducibility of velocity selective ASL (VS-ASL), which eliminates delicate label planning and possibly improves perfusion SNR by labeling closer to the target tissue. We show that abdominal VS-ASL is feasible in healthy volunteers and overcome labeling artifacts by pacing and triggering the acquisition with good temporal SNR. However, VS-ASL is sensitive to motion during readout, deteriorating reproducibility. It could benefit from outlier rejection techniques and retrospective motion correction.  

Yi Wang¹, Xingfeng Shao¹, Steen Moeller², and Danny JJ Wang^1
1Neurology, UCLA, Los Angeles, CA, United States, ²Center of Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States

The temporal SNR of simultaneous multi-slice (SMS) 2D EPI ASL has been shown to be inferior to that of 3D background suppressed GRASE. In this work, we present a novel simultaneous multi-slab (SMSB) 3D GRASE sequence for volumetric pCASL imaging with high spatial resolution. The image quality of SMSB-GRASE was evaluated and compared to a standard 3D GRASE pCASL sequence. Preliminary results demonstrated the feasibility for whole-brain volumetric perfusion imaging at a high spatial resolution, although the drop in RF slice profiles in the overlapped boundary slices still needs to be addressed in future work.

Hyo Min Lee^1,2, Marta Vidorreta^3,4, Yulin Vince Chang³, and John Alan Detre^3,4
1Bioengineering, University of Pennsylvania, Philadelphia, PA, United States, ²Institute for Biomedical Engineering, University and ETH Zürich, Zürich, Switzerland, ³Radiology, University of Pennsylvania, Philadelphia, PA, United States, ⁴Neurology, University of Pennsylvania, Philadelphia, PA, United States

ASL MRI is an appealing biomarker for clinical research and management, but ASL MRI sequences are difficult to calibrate because a reliable phantom for simulating tissue-specific perfusion has yet to be developed. In this work, we describe a prototype perfusion phantom based on 3D printed vessels and mock parenchyma that may allow reliable, ex-vivo assessments of ASL sequences.

Li Zhao¹ and David C Alsop^1
1Radiology, Beth Israel Deaconess Medical Center, Boston, MA, United States

Pseudo continuous arterial spin labeling (pCASL) studies can be degraded by magnetic field variations at the labeling plane. We demonstrate through simulations that high velocity efficiency is particularly vulnerable to field offsets. By changing labeling parameters from published recommendations and/or introducing a new RF pulse, the off-resonance sensitivity and peak systolic velocity sensitivity of pCASL can be reduced. Preliminary experimental comparisons of parameters are reported.

Thorsten Honroth¹, Suzan Vreemann², Marco Vicari¹, Hendrik Laue¹, Ritse Mann², and Matthias Günther^1,3,4
1Fraunhofer MEVIS, Bremen, Germany, ²Radboud University Medical Center, Nijmegen, Netherlands, ³University of Bremen, Bremen, Germany, ⁴mediri GmbH, Heidelberg, Germany

A single-shot 3D arterial spin labeling (ASL) sequence has been developed and optimized for breast cancer imaging. In a case study, its ability to measure the perfusion of a tumor without contrast agents is demonstrated. The resulting ASL perfusion-weighted image of the tumor shows high correspondence with the subtraction image of the contrast-enhanced measurement.

Ze Wang^1,2
1Hangzhou Normal University, Hangzhou, China, People's Republic of, ²Psychiatry and Radiology, University of Pennsylvania, PHILADELPHIA, PA, United States

ASL CBF signal is derived from the difference between successive labeling and no-labeling images. The low signal-to-noise-ratio and the pairwise subtraction can then result in outliers, which can significantly degrade CBF quantification quality in a typical several minutes scan. A priors-guided adaptive outlier cleaning algorithm was verified in this study. Our results showed that the proposed method improved both CBF quantification quality and CBF measurement stability.

Jia Guo¹, Richard B. Buxton¹, and Eric C. Wong^1,2
1Radiology, UC San Diego, La Jolla, CA, United States, ²Psychiatry, UC San Diego, La Jolla, CA, United States

The bolus duration in pulsed arterial spin labeling (PASL) is typically short, resulting in low SNR. We propose using multiple inversion pulses to increase the total bolus duration for improved SNR. In this study, a wedge-shaped inversion was combined with a regular slab inversion and a QUIPSS II pulse to lengthen the total bolus duration while keeping the ASL signal quantitative. The preliminary in vivo results showed an SNR improvement of 54% in gray matter, in good agreement with theory, compared to a regular PASL scan. The mean GM CBF values were consistent with PCASL reference scans. This new labeling method should benefit studies using PASL. 

Joshua S. Greer^1,2, Keith Hulsey², Robert E. Lenkinski^2,3, and Ananth J. Madhuranthakam^2,3
1Bioengineering, University of Texas at Dallas, Richardson, TX, United States, ²Radiology, UT Southwestern Medical Center, Dallas, TX, United States, ³Advanced Imaging Research Center, UT Southwestern Medical Center, Dallas, TX, United States

Arterial spin labeling (ASL) is a rapidly growing area of interest, primarily because of its ability to provide quantitative perfusion maps non-invasively. But, for the technique to be adopted for clinical use, these quantitative measurements need to be accurate and robust, which will require a quality controlled perfusion phantom to ensure consistency for different magnet strengths and manufacturers. In this study, we demonstrate a simple perfusion flow phantom that can be used to test the precision and repeatability of ASL perfusion measurements.

Yang Li^1,2, Deng Mao^1,2, Zhiqiang Li³, Michael Schär¹, James G. Pipe³, and Hanzhang Lu^1
1Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, MD, United States, ²Graduate School of Biomedical Sciences, University of Texas Southwestern Medical Center, Dallas, TX, United States, ³Imaging Research, Barrow Neurological Institute, Phoenix, AZ, United States

Recent studies have identified a cardiac-pulsation induced signal modulation in recommended ASL implementation (pseudocontinuous labeling 1.8s/post-labeling delay 1.8s/background-suppression/3D acquisition). In pCASL with single-shot readout, the ASL signal fluctuation could be reduced by cardiac-triggering scheme. Here is this study, we aim to extend the scope and provide possible solutions to other pCASL settings that suffer from pulsation effect, such as pCASL with 3D segmented readout, perfusion change detecting in CBF manipulations (e.g. hypercapnia), and regular pCASL when cardiac-triggering sequence is not available. We have demonstrated that considerations of cardiac phase can improve ASL data quality in multiple settings.

Jalal B. Andre¹, Swati Rane¹, Zhiqiang Li², James G. Pipe², Michael N. Hoff¹, Donna J. Cross¹, and Satoshi Minoshima^3
1Radiology, University of Washington, Seattle, WA, United States, ²Imaging Research, Barrow Neurological Institute, Phoenix, AZ, United States, ³Radiology, University of Utah, Salt Lake City, UT, United States

In this pilot project, we evaluated the effect of various readout schemes on specific ASL imaging metrics assessed by statistical 3D stereotactic surface projection, and applied to a pseudocontinuous labeling scheme that was conserved across all evaluated sequences. We conclude that descriptive statistical 3D mapping can offer insight into the performance of the five differing readout methods. 

Lydiane Hirschler^1,2, Jérome Voiron², Sascha Köhler², Nora Collomb^1,3, Emmanuel L. Barbier^1,3, and Jan M. Warnking^1,3
1Université Grenoble Alpes, Grenoble Institute of Neuroscience, Grenoble, France, ²Bruker Biospin, Ettlingen, Germany, ³Inserm, U836, Grenoble, France

Arterial Spin Labeling (ASL) is a non-invasive technique to obtain quantitative maps of perfusion. At higher magnetic fields, it benefits from both higher signal-to-noise ratio and longer T₁ but could suffer from higher RF power deposition and thus temperature increase. The latter issue has however not been characterized in animals. In this study, the specific absorption rate (SAR) delivered to a rat was measured in vivo at 9.4T using continuous ASL (CASL) and pseudo-continuous ASL (pCASL) with and without a dedicated labeling coil.

Jan Petr¹, Henri JMM Mutsaerts², Enrico De Vita^3,4, Jens Maus¹, Jörg van den Hoff¹, and Iris Asllani^5
1Institute of Radiopharmaceutical Cancer Research, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany, ²Sunnybrook Research Institute, Toronto, ON, Canada, ³Lysholm Department of Neuroradiology, National Hospital for Neurology and Neurosurgery, London, United Kingdom, ⁴Academic Neuroradiological Unit, Department of Brain Repair and Rehabilitation, UCL Institute of Neurology, London, United Kingdom,⁵Department of Biomedical Engineering, Rochester Institute of Technology, Rochester, NY, United States

Partial volume (PV) effects are a well-recognized confounder in arterial spin labeling due to its limited spatial resolution. Several algorithms exist to correct for these errors. Nevertheless, PV-correction is rarely used, mainly because the PV maps obtained from segmented T1-weighted images are regarded as not being sufficiently reliable when transformed into ASL space. Here, we show the impact of spatial deformation and resolution in the PV-maps used for PV-correction in the calculation of mean total gray matter (GM) cerebral blood flow (CBF). We also show how the deformations affect the calculation of PV-uncorrected mean GM CBF.

Jasper Verbree¹ and Matthias J.P. van Osch^1
1Radiology Department; Leiden Institute for Brain and Cognition; C.J. Gorter Center for High-field MRI, Leiden University Medical Center, Leiden, Netherlands

In pCASL, the blood tagged at the end-of-labeling period is expected to contribute most to the perfusion signal due to T1 recovery of the labeled spins. The influence on PCASL of cardiac triggering at the end-of-labeling was assessed with simulations and subsequently applied in volunteers. Simulations predict a 9% variation in ASL-signal over the cardiac cycle. In-vivo measurements were unable to show the predicted effect nor a difference in tSNR. Combining with earlier findings concerning cardiac triggering, neither triggering start- or end of labeling triggering improves signal stability, suggesting that cardiac triggering is not beneficial for pCASL.

Mayank V Jog¹, Kay Jann², Lirong Yan², and Danny JJ Wang^2
1Biomedical Engineering, University of California Los Angeles, Los Angeles, CA, United States, ²Neurology, University of California Los Angeles, Los Angeles, CA, United States

Transcranial Direct Current Stimulation (tDCS) is one of such neuromodulation techniques that applies a small current (1-2mA) using scalp electrodes. Though tDCS has been shown to improve cognition as well as clinical symptoms, the mechanism of action is still unclear.

In this study, we sought to evaluate the neurophysiological effects of tDCS in a typical bilateral motor montage through concurrent Cerebral Blood Flow (CBF) measurements using arterial spin labeling (ASL). We were able to reliably detect increased blood flow under the anode as well as CBF changes in brain-wide networks.

Henitsoa Rasoanandrianina^1,2,3,4, Aude-Marie Grapperon⁵, Manuel Taso^1,2,3,4, Olivier M. Girard^1,2, Guillaume Duhamel^1,2, Elisabeth Soulier^1,2, Lauriane Pini^1,2, Audrey Rico⁶, Bertrand Audoin⁶, Maxime Guye^1,2, Jean-Philippe Ranjeva^1,2, and Virginie Callot^1,2,3
1CRMBM UMR 7339, Aix-Marseille Université, CNRS, Marseille, France, ²CEMEREM, AP-HM, Pôle d'Imagerie Médicale, Hopital de La Timone, Marseille, France, ³iLab-Spine International Associate Laboratory, Marseille/Montréal, France, ⁴LBA UMR T 24, Aix-Marseille Université, IFSTTAR, Marseille, France, ⁵Service de Neurologie et Maladies neuro-musculaires, AP-HM,Hopital de La Timone, Marseille, France, ⁶Service de Neurologie et Unité NeuroVasculaire, AP-HM,Hopital de La Timone, Marseille, France

In this study, regional alteration of the spinal cord (SC) tissue encountered in amyotrophic lateral sclerosis (ALS) were investigated using dedicated SC templates and 3T-multiparametric MRI techniques, in particular diffusion tensor imaging (DTI) and the emerging myelin-specific inhomogeneous magnetization transfer (ihMT) technique. Results collected on 9 patients showed significant alteration of the DTI metrics compared to age-matched controls. They also demonstrated impairment of the MT metrics in the bilateral corticospinal tracts, as well as in the dorsal sensory tracts and the anterior gray matter horns. Combined with reduced ihMT metric variations, this suggests increase of the macromolecular pool, without pronounced demyelination. The structural changes we observed suggest a complex chrono-physiopathology that need to be further investigated. 

Jennifer SW Campbell¹, Ilana R Leppert¹, Mathieu Boudreau¹, Sridar Narayanan¹, Julien Cohen-Adad^2,3, G B Pike^1,4, and Nikola Stikov^2,5
1Montreal Neurological Institute, Montreal, QC, Canada, ²Ecole Polytechnique, University of Montreal, Montreal, QC, Canada, ³Functional Neuroimaging Unit, University of Montreal, Montreal, QC, Canada,⁴Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada, ⁵Montreal Heart Institute, Montreal, QC, Canada

The aggregate myelin g-ratio is a function of the myelin volume fraction (MVF) and the fiber volume fraction (FVF).  While this relationship holds in theory, obtaining precise and accurate MRI measures of the MVF and FVF remains a challenge.  Most MVF mapping techniques have been linearly correlated with histology, but the literature suggests that the slope and intercept are acquisition dependent. In this work, we focus on three magnetization transfer (MT) derived MVF metrics (MTR, MT_sat and qMT) and explore how improper calibration of the MVF estimates propagates to the aggregate g-ratio.   The result of an incorrect MVF calibration is not simply loss in sensitivity to g-ratio changes, but rather g-ratio trends that are statistically significant, incorrect, and highly dependent on the fiber volume fraction changes.

Xu Jiang^1,2, Peter van Gelderen¹, and Jeff H. Duyn^1
1AMRI, LFMI, NINDS, NIH, Bethesda, MD, United States, ²Physics, University of Maryland, College Park, MD, United States

Studying the spectral asymmetry in Magnetization Transfer (MT) is essential for precise estimation of MT-related parameters from off-resonance MT experiments. Measurement of the delay-dependent water proton saturation following composite MT pulses was used to determine parameters for a 2-pool exchange model. These parameters were further used to calculate saturation levels of macromolecular protons (MPs) following off-resonance MT pulses. The off-resonance frequency for MPs is found to be -2.7ppm from water for fixed marmoset brain, and -2.56ppm for human brain. This is consistent with previous studies.

Scott D. Swanson^1
1Department of Radiology, University of Michigan, Ann Arbor, MI, United States

This study shows that Provotorov theory of RF saturation provides an accurate description of inhomogeneous MT (ihMT) in model systems. These results help understand how long proton T1D times lead to large ihMT signals in model systems and in tissues.

Anup Singh^1,2, Mohammad Haris³, Kejia Cai⁴, Hari Hariharan⁵, and Ravinder Reddy^5
1Centre for Biomedical Enineering, Indian Institute of Technology Delhi, New Delhi, India, ²Biomedical Engineering, AIIMS Delhi, New Delhi, India, ³Research Branch, Sidra Medical and Research Center, Doha, Qatar,⁴Department of Radiology, University of Illinois at Chicago, Chicago, IL, United States, ⁵Department of Radiology, University of Pennsylvania, Philadelphia, PA, United States

Creatine(Cr) is a significant brain metabolite and its alterations has been reported in various disease conditions. In this study, chemical-exchange-saturation-transfer (CEST) MRI of Creatine(CrCEST) was performed in human brain at 7T MRI scanner. Numerical simulations were also carried out for evaluating contributions from other brain metabolites to CrCEST and a method to reduce this contamination was proposed based upon simulated data observations. Using, conventional CESTasy method, CrCEST has ~50% contribution from Cr. Using proposed subtraction based approach it is feasible to reduce contaminations from other metabolites/molecules and hence making CrCEST more specific to Cr.

Keisuke Ishimatsu¹, Karine Pozo², Shanrong Zhang¹, Koji Sagiyama¹, Osamu Togao¹, James Bibb³, and Masaya Takahashi^1
1Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, TX, United States, ²Department of Psychiatry, University of Texas Southwestern Medical Center, Dallas, TX, United States,³Department of Psychiatry / Harold C. Simmons Comprehensive Cancer Center / Department of Neurology and Neurotherapeutics, University of Texas Southwestern Medical Center, Dallas, TX, United States

The objective is to investigate whether amide proton transfer (APT) imaging is useful for evaluation of anticancer treatment responses in chemotherapy. We compared the temporal changes of APT signal with the different treatment strategies using two new drugs, administered individually or in combination, in a mouse model of medullary thyroid carcinoma.

Vitaliy Khlebnikov¹, Daniel Polders², Jeroen Hendrikse¹, Pierre A Robe¹, Eduard H Voormolen¹, Peter R Luijten¹, Dennis WJ Klomp¹, and Hans Hoogduin^1
1Radiology, University Medical Center Utrecht, Utrecht, Netherlands, ²Philips Healthcare, Best, Netherlands

The purpose of this study was to provide insight into the effect of water-T1-relaxation (T1w) on Amide Proton Transfer (APT) contrast in tumors. To this end, three different metrics of APT contrast, (mainly novel magnetization transfer ratio (MTRRex), relaxation-compensated MTRRex (AREX) and traditional asymmetry (MTRasym)) were compared in normal and tumor tissues in a variety of intracranial tumors at 7T. The strong correlation of MTRRex and MTRasym with T1w and the absence thereof in AREX suggests that much of APT contrast in tumors at 7T originates from the inherent tissue water-T1-relaxation  properties.

Nicolas Geades¹, Amal Samaraweera², William Morley¹, Matthew Cronin³, Nikos Evangelou², Penny Gowland¹, and Olivier Mougin^1
1Sir Peter Mansfield Imaging Centre, University of Nottingham, Nottingham, United Kingdom, ²Division of Clinical Neuroscience, Queen’s Medical Centre, University of Nottingham, Nottingham, United Kingdom,³Brain Imaging and Analysis Centre, Duke University, Durham, NC, United States

This study presents a method of acquiring quantitative MT and NOE concentration percentages of MS lesions over a period of 30 weeks. MT and NOE mean percentages were compared for WM lesion ROIs and NAWM ROIs, showing a clear drop of both MT and NOE when a lesion appears, followed by a gradual increase in concentrations in the following weeks, indicating remyelination. The fitting results are backed by a parallel repeatability study which shows the repeatability of the method and its noise levels. The results indicate that NOE fitting is very robust against variations in B1 compared to fitting MT.

Catherine DeBrosse¹, Ravi Nanga¹, Puneet Bagga¹, Mohammad Haris², Hari Hariharan¹, and Ravinder Reddy^1
1Center for Magnetic Resonance and Optical Imaging, University of Pennsylvania, Philadelphia, PA, United States, ²Research Branch, Sidra Medical and Research Center, Doha, Qatar

Metabolic regulation is disrupted in many diseases. As a result, the levels of lactate present in the body are often affected and implicated in disease progression and clinical outcome. To better understand lactate metabolism, an imaging technique with high sensitivity and spatial resolution is required. In this study, a chemical exchange saturation transfer (CEST) magnetic resonance imaging method, based on the exchange between lactate hydroxyl proton and bulk water protons was used to image lactate. As proof-of-principle, LATEST was implemented in vivo in exercising human skeletal muscle to image the increased lactate that results from intense exercise. 

Jochen Keupp¹, Jinyuan Zhou², and Osamu Togao^3
1Philips Research, Hamburg, Germany, ²Department of Radiology, Johns Hopkins University, Baltimore, MD, United States, ³Clinical Radiology, Kyushu University Hospital, Fukuoka, Japan

APTw MRI is an emerging technique for sensitive tissue characterization, in particular in oncology  (e.g. tumor grading). Fast-spin-echo(FSE)-Dixon acquisition techniques allow efficient and simultaneous acquisition of APT weighted (APTw) and ΔB₀ information. An improved FSE-Dixon APTw acquisition protocol with intrinsic ΔB₀ correction was implemented on a clinical MRI scanner, using multiple averages with saturation at the amide chemical shift (Δω=+3.5ppm). Contrast homogeneity was evaluated in a volunteer study and is presented together with initial clinical results on brain tumor patients.

Lukas Pirpamer¹ and Stefan Ropele^1
1Neurology, Medical University of Graz, Graz, Austria

We here present a proof of concept for a new quantitative MT mapping sequence using spin and stimulated echoes. The approach is based on the fact, that the labeled magnetization of the STEAM signal follows an double-exponential decay due to MT. With the help of a T1 map, a single acquisition with just one mixing time and an integrated spin echo allows to map the fraction of the bound proton pool.

Yajun Ma¹, Graeme Bydder¹, and Jiang Du^1
1Department of Radiology, UCSD, San Diego, CA, United States

Conventional MT modeling can only be applied to long T₂ tissues since short T₂ tissues such as cortical bone show little or no signal with clinical sequences. Ultrashort echo time magnetization transfer (UTE-MT) imaging is likely to help with this difficulty. In this study we aimed to develop and utilize UTE-MT imaging and compare two-pool with three-pool modeling of bovine cortical bone samples using a clinical 3T scanner.

Francisco Torrealdea¹, Marilena Rega¹, Sebastian Brandner¹, David Thomas¹, and Xavier Golay^1
1Brain Repair & Rehabilitation, UCL Institute of Neurology, London, United Kingdom

In this work, the feasibility of using glucoCEST as a tool for early detection of primary brain tumours is explored. Mice bearing xenograft glioblastoma tumours were scanned longitudinally using a glucoCEST protocol. The results suggest the intriguing possibility that glucoCEST contrast may be able to detect the presence of cancer at very early stage.

Antje Arnold^1,2, Yuguo Li^1,3, Guanshu Liu^1,3, Peter C.M. van Zijl^1,3, Jeff W.M. Bulte^1,2, Piotr Walczak^1,2, and Kannie WY Chan^1,3
1Radiology, Johns Hopkins University School of Medicine, Baltimore, MD, United States, ²Cellular Imaging Section and Vascular Biology Program, Institute for Cell Engineering, Baltimore, MD, United States, ³FM Kirby Research Center, Kennedy Krieger Institute, Baltimore, MD, United States

Cell therapy is showing promise in treating neurological disorders, but cell survival after transplantation is usually low, which is a major limiting factor for achieving therapeutic efficacy. One of the major hurdles in translating cell therapies to patients is the lack of non-invasive approaches to monitor the cells and their microenvironment after transplantation. We developed an injectable alginate hydrogel that supports cell survival and allows monitoring of cell status using liposomes as the nanosensors after transplantation into the brain. Hydrogel embedded cells survived better as compared to the cells without the hydrogel, and cells transplanted using the nanosensor-labeled hydrogel could be imaged using CEST-MRI.

Tao Jin¹, Bistra Iordanova¹, Ping Wang¹, and Seong-Gi Kim^2,3
1University of Pittsburgh, Pittsburgh, PA, United States, ²2Center for Neuroscience Imaging Research, Institute for Basic Science, Suwon, Korea, Republic of, ³Department of Biomedical Engineering, Sungkyunkwan University, Kuwon, Korea, Republic of

Glucose uptake and metabolism are important biomarkers for tumor diagnosis and prognosis. Recent studies showed that the glucose uptake and metabolism can be measured by a chemical exchange sensitive spin-lock (CESL) MRI approach with administration of non-labelled glucose or analogs (glucoCESL), providing unique advantage over the widely used position emission tomography technique. In this preliminary study, we evaluated the efficacy of glucoCESL for the study of brain tumor. The sensitivity and spatiotemporal characteristics of CESL signal with administration of D-Glucose, 2-deoxy-D-glucose and L-glucose were compared.

Xiang Xu^1,2, Kannie WY Chan^1,2, Huanling Liu^1,3, Yuguo Li^1,2, Guanshu Liu^1,2, Peter C.M. van Zijl^1,2, and Jiadi Xu^1,2
1Department of Radiology and Radiological Science, Johns Hopkins University, Baltimore, MD, United States, ²F.M. Kirby Research Center, Kennedy Krieger Institute, Baltimore, MD, United States, ³Department of Ultrasound, Guangzhou Panyu Central Hospital, Guangzhou, China, People's Republic of

An on-resonance variable delay multi-pulse (onVDMP) CEST technique was developed for the detection of fast-exchanging protons. The new method was applied to the detection of glucoCEST signal changes upon venous glucose injection in a mouse tumor model and compared with conventional cw-CEST method. Both methods highlight the tumor and the blood vessels upon glucose injection in mice brain implanted with brain tumors. However compared with cw-CEST, the onVDMP technique increased the tumor contrast to noise ratio by about 50% due to its sensitivity to total fast exchanging protons. 

Hoonjae Lee^1,2 and Jaeseok Park^3
1Center for Neuroscience Imaging Research (CNIR), Institute for Basic Science (IBS), Suwon, Korea, Republic of, ²Department of Brain and Cognitive Engineering, Korea University, Seoul, Korea, Republic of,³Department of Biomedical Engineering, Sungkyunkwan University, Suwon, Korea, Republic of

CEST MRI is an indirect molecular imaging technique, in which a small molecular signal is amplified by chemical exchange phenomenon. Multiple acquisition of imaging data with varying saturation frequencies, called z-spectrum acquisition, is typically performed, and then subtraction-based MTR asymmetry analysis is employed to investigate the effect of CEST on MRI. However, since the z-spectrum is additionally convoluted by inherent asymmetric MT, NOE, etc, conventional asymmetry analysis is prone to substantial errors. To tackle these problems, in this work we introduce a new, model-based extraction method of the z-spectrum asymmetry using symmetric basis (EASY) to directly characterize the signal sources of the asymmetric z-spectrum.

Bing Wu¹, Rui Li², Chien-yuan Lin³, Lin Ma², and Zhenyu Zhou^1
1GE healthcare MR Research China, Beijing, China, People's Republic of, ²PLA 301 Hospital, Beijing, China, People's Republic of, ³GE healthcare MR Research China, Taipei, Taiwan

There is a growing need for larger spatial coverage and better resolution for CEST (Chemical exchange saturation transfer). In this work, CEST acquisition based on 3D spiral was implemented and tested. Whole brain coverage could be achieved at 8s per spectral point that allows practical application. APT study showed consistent results as previous studies.  

Hoonjae Lee^1,2 and Jaeseok Park^3
1Center for Neuroscience Imaging Research (CNIR), Institute for Basic Science (IBS), Suwon, Korea, Republic of, ²Department of Brain and Cognitive Engineering, Korea University, Seoul, Korea, Republic of,³Department of Biomedical Engineering, Sungkyunkwan University, Suwon, Korea, Republic of

In chemical exchange saturation transfer (CEST) MRI, multiple acquisition of imaging data with varying saturation frequencies is typically performed, which prohibitively prolongs imaging time. Furthermore, conventional, subtraction-based MTR asymmetry analysis is prone to substantial errors, because the z-spectrum is convoluted by CEST as well as inherent asymmetric MT, nuclear Overhauser enhancement (NOE), etc. To tackle these problems, in this work we propose a new, model-based direct Extraction of the z-spectrum Asymmetry from undersampled k-space using SYmmetric basis (k-EASY) that incorporates main field inhomogeneity correction and z-spectrum asymmetry analysis into a framework of compressed sensing.

Yi Wang¹, Bing Wu², Yang Fan², and Jia-Hong Gao^1
1School of Physics, Peking University, Beijing, China, People's Republic of, ²MR Research group, GE Healthcare China, Beijing, China, People's Republic of

For quantitative analysis of CEST signal, it is crucial to decrease or eliminate the influence of parameters unrelated to chemical exchange thus emphasizing chemical exchange weight. Recently inverse Z-spectrum method realized analytical calibration but only in situation of steady state. We propose a novel analytical calibration method suitible to non-steady state situation, calculating new indexes which reflect chemical exchange weight better than those commonly used, and verifying its performance in phantom and in vivo experiment.This calibration method will be greatly helpful in quantitative CEST data analysis. 

Yin Wu^1,2, Iris Yuwen Zhou¹, Takahiro Igarashi¹, Yingkun Guo¹, Lin Li¹, and Phillip Zhe Sun^1
1Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Charlestown, MA, United States, ²Paul C. Lauterbur Research Centre for Biomedical Imaging, Shenzhen Key Laboratory for MRI, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China, People's Republic of

Renal pH was recently quantified with MR-CEST ratiometric imaging of Iopamidol at 7 T. However, the two exchangeable proton groups of Iopamidol would substantially overlap at lower magnetic field, leading to inaccurate pH quantification. Here, we investigated a Lorentzian-based decoupling algorithm to resolve the two saturation transfer effects for improved ratiometric pH measurement in rodents at 4.7 T. Results exhibits substantially enhanced range and sensitivity of pH measurements. The obtained renal pH maps are consistent with the published results. Therefore, the proposed method provides a novel way for reliable renal pH mapping, which benefits pH quantification at clinical field strengths.

Hye-Young Heo^1,2, Dong-Hoon Lee¹, Yi Zhang¹, Xuna Zhao¹, Shanshan Jiang¹, and Jinyuan Zhou^1,2
1The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, United States, ²F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States

Amide proton transfer (APT) imaging is a novel chemical exchange saturation transfer (CEST)-based MRI modality that can detect various endogenous mobile proteins and peptides in tissue, such as those in the cytoplasm. The APT quantification results depend on the CEST metrics, which is undesirable. In this study, four CEST metrics: (i) CEST ratio (CESTR), (ii) CESTR normalized with the reference value (CESTR^nr), (iii) inverse Z-spectrum-based (MTR_Rex), and (iv) apparent exchange-related relaxation (AREX), were compared using five-pool Bloch equation-based simulations with varied RF saturation powers and magnetic field strength, and in an in vivo rat tumor study at 4.7 T.

Sugil Kim^1,2 and Jaeseok Park^3
1Center for Neuroscience Imaging Research (CNIR), Institute for Basic Science (IBS), Suwon, Korea, Republic of, ²Department of Brain and Cognitive Engineering, Korea University, Seoul, Korea, Republic of,³Department of Biomedical Engineering, Sungkyunkwan University, Suwon, Korea, Republic of

To develop fast whole-brain spiral-CEST encoding with spectral and spatial correction of magnetic field inhomogeneities 

Yi Zhang¹, Hye-Young Heo¹, Dong-Hoon Lee¹, Shanshan Jiang¹, Xuna Zhao¹, Paul Bottomley¹, and Jinyuan Zhou^1,2
1Division of MR Research, Department of Radiology, Johns Hopkins University, Baltimore, MD, United States, ²F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States

CEST MRI can provide valuable molecular level information in vivo, but its translation to routine clinics is hindered by long imaging times. Regional average CEST measurements often suffice for quantitative evaluation, diagnosis, and treatment assessment, while allowing much shorter scan times. Recently, the spectroscopy with linear algebraic modeling (SLAM) method was adapted for CEST MRI in two dimensions (2D), directly obtaining compartmental-average measurements manifold faster than conventional CEST. Here, the SLAM CEST method is extended from 2D to 3D, and applied to patients with brain tumors with acceleration factors of up to 98-fold.

Catalina S. Arteaga de Castro¹, Hans J.M. Hoogduin¹, Vitaliy Khlebnikov¹, Peter R. Luijten¹, Dennis W.J. Klomp¹, and Moritz Zaiss^2
1Imaging Division, University Medical Center Utrecht, Utrecht, Netherlands, ²Medical Physics in Radiology, German Cancer Research Center, Heidelberg, Germany

The feasibility of selective NOE- and amide-CEST detection in the prostate at 7T was investigated with a multi-transmit system. Both effects can be acquired simultaneously due to the increased sensitivity and spectral resolution available at 7T. Fitted NOE- and amide-CEST were reproducible within experiments. NOE-CEST was found to be more pronounced than amide-CEST in small and whole prostate ROIs and the peripheral zone showed the lowest amide- and NOE-CEST effects.

Yi Zhang¹, Hye-Young Heo¹, Dong-Hoon Lee¹, Paul Bottomley¹, and Jinyuan Zhou^1,2
1Division of MR Research, Department of Radiology, Johns Hopkins University, Baltimore, MD, United States, ²F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States

CEST imaging has numerous applications, but its widespread clinical use is hampered by relatively long acquisition times. Here, a novel variably-accelerated sensitivity encoding (vSENSE) method is proposed that provides faster CEST acquisitions than conventional SENSE. The vSENSE approach undersamples k-space variably for images acquired at different saturation frequencies to maximize acquisition speed. vSENSE was validated in a phantom and in 8 patients with brain tumors studied at 3T. The vSENSE method provided a 4-fold acceleration, compared to conventional SENSE which permitted only a 2-fold acceleration, with both compared to a full k-space reconstruction.

Johannes Windschuh¹, Moritz Zaiss¹, Jan-Eric Meissner¹, Steffen Goerke¹, and Peter Bachert^1
1Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany

We investigated the dependencies of the exchange-relayed Nuclear Overhouser Effect (rNOE) observable in Chemical Exchange Saturation Transfer (CEST) experiments on tissue integrity and static magnetic field strength B₀. By comparison of a homogenized and native sample of white matter tissue of animal brain we could show that the CEST signal of the aliphatic rNOE is independent of  tissue structure. The observed increase of all CEST effects on decrease of B₀ probably results from relatively broader saturation bandwidth at lower field strengths. No indication for a rNOE dependency on B₀ differing from that of chemical exchange effects could be found.

Alexia Daoust¹, Stephen Dodd¹, Govind Nair¹, Steven Jacobson¹, Daniel Reich¹, and Alan Koretsky^1
1NINDS, NIH, Bethesda, MD, United States

There continues to be interest in using changes in CSF properties to image neurodegenerative diseases. To optimize MRI sequences that enable segmentation of CSF from tissue, we characterized the CSF relaxometric properties at various field strengths in vivo and in vitro. Our in vitro results suggest that in vivo T₂ value at high field is incorrect due to residual gradients and that low field is more optimal to quantify CSF relaxivity in vivo. We have shown an important difference of in vitro CSF T₂ vs saline T₂ that is mostly explained by the relaxivity of glucose.

Mobeen Ali¹, Penny Gowland¹, and Richard Bowtell^1
1SPMIC, School of Physics and Astronomy, University of Nottingham, Nottingham, United Kingdom

Comparison of post mortem and in vivo MR images requires an understanding of the temperature dependence of the NMR parameters that generate relevant image contrast. Here, we therefore evaluated the temperature dependence of the susceptibility and relaxivity of ferritin-doped agar. A phantom containing cylinders doped with different ferritin concentrations was scanned at 7T at temperatures ranging from 5–35°C. R1, R2* and field maps were generated and the variation of each parameter with ferritin concentration was evaluated. The variations of susceptibility, R2* and R1 with ferritin concentration all decreased with increasing temperature with R2* showing the strongest temperature dependence.  

Reza Basiri¹, Marc Lebel², and Paolo Federico^3
1Biomedical Enginnering, University of Calgary, Calgary, AB, Canada, ²Alberta Children's Hospital Research Institute, Calgary, AB, Canada, ³Foothills Hospital, Calgary, AB, Canada

Quantitative T₂ mapping provides diagnostic capabilities complementing standard qualitative imaging. However, conventional fitting algorithms to estimate T₂ are prone to bias. In this work, we propose a fitting method that remains applicable to existing datasets while addressing many of the imperfections and shortcomings of current methods. Our proposed method is an extension of stimulated echo correction that highly constrains the estimated transmit field. It was evaluated using simulated and experimental data. We found that variance in the T₂ estimate could be reduced by ~25% in certainly realistic conditions while maintaining full accuracy relative to the current stimulated echo corrected fit. Transverse relaxometry, a quantitative T₂ mapping has shown superior diagnostic capabilities compare with qualitative maps for neurological diseases. However, the conventional fitting Quantitative T₂ mapping provides diagnostic capabilities complementing standard qualitative imaging. However, conventional fitting algorithms to estimate T₂ are prone to bias. In this work, we propose a fitting method that remains applicable to existing datasets while addressing many of the imperfections and shortcomings of current methods. Our proposed method is an extension of stimulated echo correction that highly constrains the estimated transmit field. It was evaluated using simulated and experimental data. We found that variance in the T₂ estimate could be reduced by ~25% in certainly realistic conditions while maintaining full accuracy relative to the current stimulated echo corrected fit.

Alexander L Sukstanskii¹, Jie Wen¹, Anne H Cross², and Dmitriy A Yablonskiy^1
1Mallinckrodt Institute of Radiology, Washington University, Saint Louis, MO, United States, ²Neurology, Washington University, Saint Louis, MO, United States

The cross-relaxation effects between “free” and “bound” water affect the gradient recalled echo (GRE) MRI signal and can bias quantitative measurements of tissue relaxation parameters. Herein we have generalized the classical Ernst equation for the GRE signal dependence on sequence parameters (echo and repetition times, flip angle) by accounting for cross-relaxation effects. The derived equation creates a basis for a new technique - Simultaneous Multi-Angular Relaxometry of Tissue with Magnetic Resonance Imaging (SMART MRI). The technique allows simultaneous quantitative measurements of longitudinal and transverse relaxation rates constants and some essential cross-relaxation parameters without utilizing off-resonance magnetization transfer pulses.

Thibo Billiet¹, Stefan Sunaert¹, Bea Van den Bergh¹, Ronald Peeters¹, Mathieu Vandenbulcke¹, and Louise Emsell^1
1KU Leuven, Leuven, Belgium

Currently, only single slice repeatability results for myelin water imaging (MWI) metrics are available. We assessed the within- and between-subject variation of the myelin water fraction (MWF); intra- and extracellular water fraction (IEWF), and intra- and extracellular water geometric mean T2 time (IEW-gmT2) in a whole cerebrum MWI sequence¹ We demonstrated good within- and between subject variability, comparable to previous single-slice results. Future studies may benefit from sample size estimations documented in this work.

Martina F Callaghan¹, Kerrin J Pine¹, Karsten Tabelow², Joerg Polzehl², Nikolaus Weiskopf^1,3, and Siawoosh Mohammadi^1,4
1Wellcome Trust Centre for Neuroimaging, UCL Institute of Neurology, London, United Kingdom, ²Weierstrass Institute, Berlin, Germany, ³Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, ⁴Department of Systems Neuroscience, University Medical Center Hamburg-Eppendorf, Hamburg, Germany

In vivo histology aims to extract biologically relevant metrics from MRI data. In neuroimaging this includes characterising white matter fibres in terms of orientation, distribution and g-ratio, or determining the cortical myelo- and cyto-architecture. It has been shown, both theoretically and experimentally, that the signal decay in gradient recalled echoes (GRE) exhibits higher order temporal behaviour that is dependent on a variety of intra-voxel microstructural metrics. Here we use adaptive smoothing to generate maps of both the first and second order components of the temporal decay of the GRE signal from short TE data using a time-efficient multi-parameter mapping protocol.

Peter van Gelderen¹ and Jeff H Duyn^1
1Advanced MRI, LFMI NINDS, National Institutes of Health, Bethesda, MD, United States

The longitudinal relaxation rate (R₁) of MRI-invisible macro-molecular protons is an important parameter in the generation of MT and T₁ contrast. Despite this, considerable uncertainty exists about its actual value. To address this MT and inversion recovery experiments were jointly analyzed with a 2-pool model of exchange, and estimates were derived for human brain at 3T and 7T.

Veronica Cosi¹, Akio Ernesto Yoshimoto², Timothy Shepherd^2,3, KAI Tobias Block^2,3, Daniel K Sodickson^2,3, and Noam Ben-Eliezer^2,3
1Department of Specialised, Experimental, and Diagnostic Medicine, University of Bologna, Bologna, Italy, ²Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, NY, United States, ³Center for Advanced Imaging Innovation and Research (CAI2R), New York University School of Medicine, New York, NY, United States

Accurate quantification of T₂ values in vivo poses a long-standing challenge, hampered by the inherent bias of fast multi-SE protocols by stimulated and indirect echoes, non-rectangular slice profile and transmit-field inhomogeneities. This bias, moreover, is dependent on the sequence implementation and parameter-set employed, and thus varies between scanners and vendors.  We present full stability and reproducibility tests of a recently developed T₂ mapping technique – the echo-modulation curve (EMC) algorithm – which uses precise Bloch simulations of the pulse-sequence scheme to deliver the true T₂ value of the tissue in a manner that is independent of the parameter-set and scanner being used.

Vasileios Zampetoulas¹, Lionel M. Broche¹, and David J. Lurie^1
1Aberdeen Biomedical Imaging Centre, School of Medicine & Dentistry, University of Aberdeen, Foresterhill, AB25 2ZD, Aberdeen, United Kingdom, Aberdeen, United Kingdom

A graph of T₁ versus magnetic field obtained via Fast Field-Cycling (FFC) NMR relaxometry techniques can be developed into a new diagnostic tool thanks to the information about molecular dynamics that it provides. In this work, a novel method that compensates for the environmental fields acting on an FFC relaxometer is analysed, and applied to acquire measurements in the µT region for the study of much slower molecular motions, that was not previously possible. The results acquired from human cartilage indicate motions occurring in a slow time scale (0.1 to 10 ms), which show promise for clinical studies.  

Peter Wright¹, Hannah Webley², Andrew Fry¹, and Elspeth Whitby^2
1MIMP, Sheffield Teaching Hospitals NHS Foundation Trust, Sheffield, United Kingdom, ²Academic Unit of Reproductive and Developmental medicine, University of Sheffield, Sheffield, United Kingdom

Subdural haematoma (SDH) resulting from traumatic brain injury relating to non accidental head injury is unfortunately relatively common in the UK at 36 per 100000 incidence in children < 6 months old. However, adult models are used when aging SDH. This study aimed to compare calculated relaxation time constants, T₂^* and T₁ of fetal and adult blood samples in a simulated SDH for data acquired daily over 28 days. Significant differences between fetal and adult were found in T₂^* and T₁ values for week 1 and weeks 1, 3 and 4 respectively.

Meher Juttukonda¹, Manus Donahue¹, Melissa Gindville², and Lori Jordan^2
1Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, United States, ²Pediatrics, Division of Pediatric Neurology, Vanderbilt University Medical Center, Nashville, TN, United States

Quantitative CBF maps derived from pseudo-continuous ASL (pCASL) may be useful in assessing stroke risk in sickle cell anemia (SCA) patients, but T₁ relaxation of SCA blood must first be characterized. Venous blood samples were collected from SCA patients as well as normal subjects, and an inversion recovery approach was used to quantify the T₁ relaxation times ex vivo. For similar hematocrit, oxygenation, and temperature, T₁ relaxation times of SCA blood appear similar to those of normal blood. Therefore, computation of CBF in SCA patients may not be affected by the assumption of normal blood T₁ relaxation.

Mahesh Bharath Keerthivasan¹, Lindsie Jeffries², Diego Blew³, Jean-Philippe Galons³, Puneet Sharma³, Ali Bilgin^1,2,3, Diego R Martin³, and Maria I Altbach^3
1Electrical and Computer Engineering, University of Arizona, Tucson, AZ, United States, ²Biomedical Engineering, University of Arizona, Tucson, AZ, United States, ³Medical Imaging, University of Arizona, Tucson, AZ, United States

There has been increased interest in the quantitative characterization of tissue based on T2. Techniques based on spin-echo (SE) or fast spin-echo (FSE) sequences are time consuming because they require multiple acquisitions for obtaining an adequate number of TE images for accurate T2 mapping. Radial FSE based methods have been introduced for efficient T2 mapping by using TE data from a single k-space data set. In this work, we explore combining the Echo Sharing algorithm for the fast reconstruction of the TE images with SEPG model fitting to compensate for indirect echoes. 

Li Zhao¹, Yang Yang², Chuan Huang³, and Craig Meyer^2
1Radiology, Beth Israel Deaconess Medical Center, Boston, MA, United States, ²Biomedical Engineering, University of Virginia, Charlottesville, VA, United States, ³Departments of Radiology, Psychiatry, Stony Brook Medicine, Stony Brook, NY, United States

Parameter mapping can be acquired rapidly by MR fingerprinting. It requires a pseudo random pulse sequence to build an unique dictionary between the evolution of signal and parameters. The problem can be simplified when the dimension of the dictionary is relatively low. Here, we propose a dictionary that accelerates T2 mapping with dictionary and conventional sequence.

Tom Hilbert^1,2,3, Jean-Philippe Thiran^2,3, Reto Meuli², Gunnar Krueger^2,3,4, and Tobias Kober^1,2,3
1Advanced Clinical Imaging Technology (HC CMEA SUI DI BM PI), Siemens Healthcare AG, Lausanne, Switzerland, ²Department of Radiology, University Hospital (CHUV), Lausanne, Switzerland, ³LTS5, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland, ⁴Siemens Medical Solutions USA, Inc., Boston, MA, United States

Numerous iterative reconstruction techniques have been published in the past, facilitating the calculation of quantitative parameter maps based on undersampled k-space data. Model-based approaches, for example, iteratively minimize a cost function that comprises a formulation of the signal behavior. Minimizing this non-linear problem yields the quantitative parameter maps, but is numerically challenging and thus accompanied with reduced robustness and long reconstruction times compared to a direct Fourier transform. Here we suggest a method to split the optimization problem of a model-based T2 mapping into sub-problems which are solved alternately. The splitting results in a more robust reconstruction with less computational cost.

Yoojin Lee^1,2, Martina F. Callaghan³, and Zoltan Nagy^1
1Laboratory for Social and Neural Systems Research, University of Zürich, Zürich, Switzerland, ²Institute for Biomedical Engineering, ETH Zürich, Zürich, Switzerland, ³Wellcome Trust Centre for Neuroimaging, UCL Institute of Neurology, London, United Kingdom

Rational approximation of the SPGR signal provides a simple algebraic expression of T₁ within the VFA framework. For this method, we derive an analytical solution of how the precision in T₁ maps depends on the noise in the B₁⁺ map as well as the component SPGR images. We show that the derived equation provides a good prediction of the noise in T₁ measured in-vivo. Further, we show that B₁⁺ maps can introduce as much noise into the T₁ maps as the SPGR images for equal input variance.

Atsushi M Takahashi^1
1McGovern Institute for Brain Research, Massachusetts Institute of Technology, Cambridge, MA, United States

Quantitation of  T₂* with spiral imaging sequences can be made in two distinct ways: Collecting data at various echo-times results in a measurement of the chemical shift after Fourier transformation along the echo-time dimension. Off resonance is intrinsically corrected by this processing. Alternately, multiple-echo spiral imaging can be used to quantitatively measure T2* as long as dephasing from B₀ distortion is small over the duration of the spiral readout. Multiple spiral interleaves are used to reduce the readout time of the spiral. Both methods are demonstrated.

Youngwook Kee¹, Kofi Mawuli Deh¹, Pascal Spincemaille¹, and Yi Wang^1
1Weill Cornell Medical College, New York, NY, United States

Since QSM has been recently undergoing clinical trials and the MEDI toolbox plays an important role for this purpose, numerical implementation should be consistent in the sense of continuum limit. In this abstract, we point out a numerically inconsistent finite difference scheme that has been used in the MEDI toolbox and show that by replacing it with a consistent one it drastically improves image quality.

Ferdinand Schweser^1,2, Paul Polak¹, Nicola Bertolino¹, and Robert Zivadinov^1,2
1Buffalo Neuroimaging Analysis Center, Department of Neurology, Jacobs School of Medicine and Biomedical Sciences, The State University of New York at Buffalo, Buffalo, NY, United States, ²MRI Molecular and Translational Research Center, Jacobs School of Medicine and Biomedical Sciences, The State University of New York at Buffalo, Buffalo, NY, United States

Despite increasing exploration of quantitative susceptibility mapping (QSM) in humans and the method's potential to study tissue iron pre-clinically, only few studies have yet applied QSM in alive rodents at ultra-high magnetic field strength. In the present work we hypothesized that the low quality of pre-clinical QSM compared to human QSM is due to the combination of a similar level of non-susceptibility phase contributions with much lower susceptibility variations. Here, we propose a new type of QSM algorithm that accounts for non-susceptibility phase effects and, hence, enables pre-clinical QSM: QUAntitative Susceptibility And Residual mapping (QUASAR).

Jingu Lee¹, Woojin Jung¹, Yoonho Nam², and Jongho Lee^1
1Laboratory for Imaging Science and Technology, Department of Electrical and Computer Engineering, Seoul National University, Seoul, Korea, Republic of, ²Department of Radiology, Seoul St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea, Republic of

In this work, we measured the effect size of both myelin concentration and fiber orientation in R₂*. Additionally, we generated the myelin concentration and/or fiber orientation bias free R₂* maps which may have important applications.

Surabhi Sood¹, Javier Urriola¹, David Reutens¹, Steffen Bollmann¹, Kieran O'Brien², Markus Barth¹, and Viktor Vegh^1
1Centre for Advanced Imaging, The University of Queensland, Brisbane, Australia, ²Siemens Ltd., Brisbane, Australia

Quantitative susceptibility mapping is an important magnetic resonance imaging tool which can help define brain structure and composition. Our work aims to explore information contained in the temporal trend by analysing the mapped magnetic susceptibility as a function of echo time from gradient recalled data acquired at 7T. Temporal susceptibility plots were studied in ten brain regions. Parameterisation of image voxel susceptibility compartments has the potential to delineate structural and chemical changes in tissue and formulate biologically meaningful measures. This in turn provides a framework for new imaging biomarker developments in neurodegenerative diseases and disorders affecting the central nervous system.  

Emma Biondetti¹, David L. Thomas², and Karin Shmueli^1
1Department of Medical Physics and Biomedical Engineering, University College London, London, United Kingdom, ²Leonard Wolfson Experimental Neurology Centre, UCL Institute of Neurology, University College London, London, United Kingdom

In Susceptibility Mapping (SM) using multi-echo gradient-echo phase data, unwrapping and/or background-field removal is often performed using Laplacian-based methods. However, SM pipelines in the literature have applied these methods at different stages. Here, using simulated and acquired images, we compared the performance of three pipelines that apply Laplacian-based methods at different stages. We showed that Laplacian-based methods alter the linearity of the phase over time. We demonstrated that only a processing pipeline that takes this into account, i.e. by fitting the multi-echo data over time to correctly estimate a field map before applying Laplacian-based methods, gives accurate susceptibility values.

Xinxin Zhao¹, Hedi An², Tian Liu³, Nan Shen², Binshi Bo⁴, Zhuwei Zhang⁴, Pengfei Weng⁴, Meining Chen⁴, Mengchao Pei⁴, Yi Wang^3,4, Dongya Huang², and Jianqi Li^4
1Shanghai Key Laboratory of Magnetic Resonance and Department of Physics, East China Normal University, Shanghai, China, People's Republic of, ²Dongfang Hospital Neural Medical Affiliated Tongji University, Shanghai, China, People's Republic of, ³Department of Radiology, Weill Medical College of Cornell University, New York, NY, United States, ⁴Department of physics, Shanghai Key Laboratory of Magnetic Resonance and Department of Physics, East China Normal University, Shanghai, China, People's Republic of

Quantitative susceptibility mapping (QSM) provides excellent contrast of iron-rich deep nuclei to quantify iron in the brains. Clinicians are interested in using QSM to diagnose PD patients. QSM and R2* values were measured in the whole substantia nigra in patients with PD and healthy controls. The significant difference between PD patients and healthy controls in the substantia nigra was found on QSM but not on R2* mapping.

Sina Straub¹, Till Schneider^2,3, Christian H. Ziener³, Heinz-Peter Schlemmer³, Mark E. Ladd¹, Frederik B. Laun¹, and Martin T. Freitag^3
1Department of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany, ²Department of Neuroradiology, University of Heidelberg, Heidelberg, Germany, ³Department of Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany

The benefit of susceptibility weighted imaging (SWI) and quantitative susceptibility mapping (QSM) for the detection and quantification of bleeding of brain metastases of malignant melanoma is assessed. QSM shows paramagnetic values for hemorrhagic metastases (0.355±0.097 ppm) and less paramagnetic values (0.239±0.123 ppm) for hemorrhagic metastases that have T1w-native hyperintense signal. Moreover, our findings suggest that T1w-native hyperintense melanoma metastases have relatively diamagnetic susceptibility compared to other structures of the brain.

Dong Zhou¹, JingWei Zhang², Pascal Spincemaille¹, and Yi Wang^1,2
1Radiology Department, Weill Cornell Medical College, New York, NY, United States, ²Biomedical Engineering, Cornell University, Ithaca, NY, United States

The error in digitizing the dipole convolution¹ may become substantial when there is abrupt susceptibility change within a voxel. To evaluate this error, we assessed the accuracy of quantitative susceptibility mapping in a gadolinium balloon phantom with a range of large susceptibility values (0.4 – 3.2 ppm) and imaging resolutions (0.7 – 1.8 mm) at both 1.5T and 3T. Systematic underestimation of the susceptibility values was observed with decreasing imaging resolution. Numerical simulations were performed to match the experimental findings. These show that the underestimation originates directly from the changes in the voxel sensitivity function and that the amount of underestimation is affected not only by imaging resolution, but also magnitude contrast, the use of k-space filters in the image reconstruction, and details of the susceptibility inclusions such as the susceptibility value and geometry.

Vanessa Wiggermann^1,2, Enedino Hernandez-Torres^2,3, Inga C Ibs⁴, Stephanie M Schoerner⁵, Galina Vorobeychik⁶, Luanne Metz⁷, David KB Li^8,9, Anthony Traboulsee^9,10, and Alexander Rauscher^2,9,11
1Physics and Astronomy, University of British Columbia, Vancouver, BC, Canada, ²Pediatrics, University of British Columbia, Vancouver, BC, Canada, ³UBC MRI Research Centre, University of British Columbia, Vancouver, BC, Canada, ⁴University of Osnabrueck, Osnabrueck, Germany, ⁵Technical University of Dortmund, Dortmund, Germany, ⁶Fraser Health MS Clinic, Burnaby, BC, Canada, ⁷Clinical Neurosciences, University of Calgary, Calgary, AB, Canada, ⁸Radiology, University of British Columbia, Vancouver, BC, Canada, ⁹Center for Brain Health, University of British Columbia, Vancouver, BC, Canada, ¹⁰Medicine (Neurology), University of British Columbia, Vancouver, BC, Canada, ¹¹Child and Family Research Institute, University of British Columbia, Vancouver, BC, Canada

Using magnetic-susceptibility based MR techniques for the assessment of damage due to multiple sclerosis (MS) has been controversial, in particular in MS lesions where the underlying pathological changes are not yet fully understood. Here, we investigated the changes of the MR frequency and quantitative susceptibility signal during acute MS lesion formation. We observed that both metrics behave similarly, indicating that non-local effects have little contribution to the QSM signal increase and hence dipole inversion might not be required to assess damage during MS lesion formation accurately.

Nan-Jie Gong¹, Hing-Chiu Chang², Hongjiang Wei¹, Mark Sundman¹, Nan-kuei Chen¹, and Chunlei Liu^1
1Brain Imaging and Analysis Center, Duke University, Durham, NC, United States, ²Diagnostic Radiology, The University of Hong Kong, Hong Kong, China, People's Republic of

We demonstrated the feasibility of using the proposed phase correction method for increasing the accuracy of QSM reconstruction from multi-band acquisitions. With multi-band acquisition, we were able to greatly shorten data acquisition time. It is expected that facilitate this method would benefit further clinical application of QSM and QSM based cerebral functional and physiological studies.

Yuya Umemoto¹, Tomohiro Ueno¹, Shin-ichi Urayama², Toshihiko Aso², Hidenao Fukuyama², and Naozo Sugimoto^1
1Human Health Sciences, Kyoto University, Kyoto, Japan, ²Human Brain Research, Kyoto University, Kyoto, Japan

In Quantitative Susceptibility Mapping, susceptibility distribution can be obtained by deconvolution of perturbed fields with dipole fields. In our proposed method, High Resolution QSM, we employed densely sampled dipole fields to improve the quality of QSM. To verify the High Resolution QSM, we performed a human study, and acquired QSM input phase data of a healthy human subject. We compared MIP of the High Resolution QSM to that of the tricubically interpolated conventional QSM. In the High Resolution QSM, visibility of several cerebral blood vessels is improved. This means that a susceptibility map with higher spatial resolution is obtained.

Elena Kleban¹, Benjamin Tendler¹, Penny Gowland¹, and Richard Bowtell^1
1The Sir Peter Mansfield Imaging Center, School of Physics and Astronomy, Nottingham, United Kingdom

The purpose of this work was to investigate the microstructural properties of white matter in the human brain using  saturation recovery multi-echo GE imaging at 7T.

Multi gradient-echo data acquired at three different flip-angles from 8 healthy subjects was fitted for corpus callosum to a three-pool model describing the axonal, myelin and external compartments and variation of the relative amplitude of the myelin water signal with flip-angle was used to assess the T₁ values of the different compartments. Results show an increased frequency variation with TE and faster magnitude signal decay at higher flip-angles, consistent with reduced T­₁ in the myelin water compartment.

Anita Karsa¹, Emma Biondetti¹, Shonit Punwani², and Karin Shmueli^1
1Medical Physics and Biomedical Engineering, University College London, London, United Kingdom, ²Centre for Medical Imaging, University College London, London, United Kingdom

Susceptibility Mapping has emerging clinical applications. To reduce scan time, clinical images are often acquired with large slice spacing/thickness and reduced coverage. The effect of these factors on susceptibility maps has not been investigated. Here, we develop a simple framework to explore the effect of low-resolution and low-coverage in the slice dimension on the accuracy of susceptibility maps. Our experiments with digital phantoms and volunteer images have shown that the error in the estimated susceptibility increases substantially with increasing slice spacing/thickness and decreasing coverage. These results underscore the need for high-resolution, full-coverage acquisitions for accurate susceptibility mapping.

Daniel Stäb^1,2, Steffen Bollmann¹, Christian Langkammer³, Kristian Bredies⁴, and Markus Barth^1
1The Centre for Advanced Imaging, The University of Queensland, Brisbane, Australia, ²Department of Diagnostic and Interventional Radiology, University of Würzburg, Würzburg, Germany, ³Department of Neurology, Medical University of Graz, Graz, Austria, ⁴Institute for Mathematics and Scientific Computing, University of Graz, Graz, Austria

Ultra-high field whole brain susceptibility mapping at an isotropic resolution of 1 mm was performed within 16 seconds using a 3D planes-on-a-paddlewheel (POP) EPI sequence. The non-Cartesian readout scheme is created by rotating a standard EPI readout train around its own phase encoding axis and provides higher flexibility for echo time minimization than conventional 3D EPI. Morphologic images and susceptibility maps obtained were comparable to those acquired with a conventional 4 minute 3D GRE scan.

Toru Shirai¹, Ryota Sato¹, Yo Taniguchi¹, Takenori Murase², Atsushi Kuratani², Taisei Ueda², Takashi Tsuneki², Yoshitaka Bito², and Hisaaki Ochi^1
1Research and Development Group, Hitachi, Ltd., Tokyo, Japan, ²Healthcare Campany, Hitachi, Ltd., Chiba, Japan

    We have proposed that a QSM reconstruction method combining an iterative least square minimization and adaptive edge-preserving filtering could generate high-quality susceptibility maps. In this study, maps calculated by the proposed method were compared qualitatively and quantitatively with those calculated by COSMOS (a calculation of susceptibility through multiple-orientation sampling) in healthy volunteers. The results from human brain experiments showed good agreement with COSMOS. The proposed QSM reconstruction of single orientation sampling is useful for generating a high-quality susceptibility map of the human brain.

M Louis Lauzon^1,2,3, Cheryl Rae McCreary^1,2,3, D Adam McLean^3,4, Marina Salluzzi^3,4, and Richard Frayne^1,2,3
1Radiology and Clinical Neurosciences, University of Calgary, Calgary, AB, Canada, ²Hotchkiss Brain Institute, Calgary, AB, Canada, ³Seaman Family MR Research Centre, Calgary, AB, Canada, ⁴Calgary Image Processing and Analysis Centre, Calgary, AB, Canada

We scanned 4 volunteers 3 times each using 8 different QSM variants (unipolar/bipolar readout gradient, accelerated or not, with/without gradient warp-correction), and compared the susceptibility (average and standard deviation) in five deep gray matter tissues using linear mixed effects modeling. Gradient-warp correction was found to decrease the susceptibility estimates by 3-5%, whereas there was no statistical difference in the estimates due to readout polarity or acceleration factor.

Taichiro Shiodera¹, Takamasa Sugiura¹, Yuko Hara¹, Yasunori Taguchi¹, Tomoyuki Takeguchi¹, Masao Yui², Naotaka Sakashita², Yasutaka Fushimi³, Takuya Hinoda³, Tomohisa Okada³, Aki Kido³, and Kaori Togashi^3
1Toshiba Corporation, Kawasaki, Japan, ²Toshiba Medical Systems Corporation, Otawara, Japan, ³Kyoto University Graduate School of Medicine, Kyoto, Japan

We propose a background phase removal method for quantitative susceptibility mapping using adaptive kernels depending on brain region. Conventional methods use distance adaptive kernel spherical mean values (SMV) to estimate background phase. However, artifacts occur where kernel sizes are not optimal for certain brain regions. Here, we adapt SMV kernel sizes depending on brain regions which are automatically detected by machine learning methods. The proposed method eliminates tissue phase artifacts near air-tissue interfaces in more central areas such as the sinus. The proposed method also eliminates streak artifacts in susceptibility images.

Timothy J Colgan^1,2, Diego Hernando¹, Samir Sharma¹, Debra E Horng^1,2, and Scott B Reeder^1,2,3,4,5
1Radiology, University of Wisconsin, Madison, WI, United States, ²Medical Physics, University of Wisconsin, Madison, WI, United States, ³Biomedical Engineering, University of Wisconsin, Madison, WI, United States,⁴Medicine, University of Wisconsin, Madison, WI, United States, ⁵Emergency Medicine, University of Wisconsin, Madison, WI, United States

MR-based Quantitative Susceptibility Mapping (QSM) techniques have multiple potential applications in brain and body imaging. QSM techniques generally rely on the removal of background field effects to obtain a local B0 map, followed by dipole inversion to estimate the underlying susceptibility distribution. However, concomitant gradients introduce significant unanticipated phase shifts in the acquired data that manifest as errors in the measured B0 field map. Our results demonstrate that CG phase corrections and/or the use of a background field removal algorithm that removes this background field component are necessary for accurate QSM.

Job Gijsbertus Bouwman¹ and Peter R Seevinck^1
1Image Sciences Institute, University Medical Center Utrecht, Utrecht, Netherlands

Quantitative Susceptibility Mapping reconstructions may benefit from L1-regularization and magnitude weighing, however these iterative reconstruction methods are time-consuming. Recently, progression has been made in reducing the reconstruction times with Split Bregman iterations, allowing subject-specific regularization weights. Here a further reduction of the reconstruction time is reported, mostly based on accelerating the automatic selection of the optimal regularization parameter. The overall procedure reduces computational load more than threefold, without accuracy loss. Reduction of reconstruction times, may contribute to realize QSM algorithms which are either clinically feasible, or that may pave the way to include more sophisticated regularization mechanisms.

Scott C Beeman¹, Joseph JH Ackerman¹, and Joel R Garbow^1
1Washington University in St. Louis, St. Louis, MO, United States

A direct and non-invasive measure of tissue O₂ would be a major advance. O₂ is paramagnetic and can thus, in principle, be quantified with NMR/MRI. However, such measurements are challenged/masked by two competing effects: (i) magnetization transfer between ¹H spins of tissue water and the solid-like macromolecular matrix (e.g., proteins, cell membranes) and (ii) blood flow, which can bring equilibrium-polarized ¹H spins into the interrogated tissue volume. We describe a strategy for mitigating these confounds and quantify the direct relationship between pO₂ and the MR-measured longitudinal relaxation rate constant, R₁.

romain valabregue¹ and Ludovic De Rochefort^2
1CENIR, ICM, Inserm U 1127, CNRS UMR 7225, Sorbonne Universités, UPMC Univ Paris 06 UMR S 1127F, Paris, France, ²IR4M (Imagerie par Résonance Magnétique Médicale et Multi-modalités), Univ. Paris-Sud, CNRS, UMR8081, Université Paris-Saclay, Orsay, France

A criterion of A-optimality was used to optimize SSFP sequence acquisition parameters in order to perform multi-parametric mapping of the physical parameters proton density, relaxation rates and apparent diffusion coefficient. A fast calculation of the steady-state was used to estimate the Fisher information matrix from which fitted parameter error was determined from its inverse. Considering a range of possible T1 and T2 values, and relevant ADC, the acquisition parameters were optimized over the four dimensions of TR, prescribed flip angle, RF phase increment and spoiling gradient to achieve the minimum error on the effectively fitted physical parameters. It is demonstrated that choosing targeted T1 and T2 values over a wide range of expected values enables defining acquisition protocols that minimize the error over this range.

Bridgette Webb¹, Thomas Widek¹, Bernhard Neumayer¹, Rudolf Stollberger², and Thorsten Schwark^1,3
1Ludwig Boltzmann Institute for Clinical Forensic Imaging, Graz, Austria, ²Institute of Medical Engineering, Graz University of Technology, Graz, Austria, ³Institute of Legal Medicine, Medical University of Graz, Graz, Austria

MRI evaluation of a post-mortem reperfused cardiovascular system requires a complete filling of vessels, acceptable contrast/image quality and consideration of temperature influences.  Assessment of the temperature dependence of viscosity, T1 and T2 of candidate perfusates (n=10) found 3 to be suitable for application in post-mortem MR angiography. Bloch equation simulations were applied to investigate contrast between these liquids and post-mortem myocardium at 1, 8.5, 16 and 23°C. For a FLASH sequence, optimal flip angles were affected by temperature variation and a decrease in contrast (max. 6-12%) was observed when flip angles optimised for one of the other temperatures were applied.

Miko H. de Haas^1,2, Huihui Ye^2,3, Howard H. Chen^2,4, Eric M. Gale^2,4, Eszter Boros^2,4, Peter Caravan^2,4, Kawin Setsompop^2,4, and David E. Sosnovik^2,4
1Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands, ²Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, United States, ³Collaborative Innovation Center for Brain Science and the Key Laboratory for Biomedical Engineering of Education Ministry of China, Zhejiang University, Hangzhou, China, People's Republic of,⁴Department of Radiology, Harvard Medical School - Massachusetts General Hospital, Boston, MA, United States

MR contrast agents are typically imaged using time-consuming sequences, which allows only one parameter of relaxation to be assessed. In this research we used Magnetic Resonance Fingerprinting (MRF) to rapidly assess both T₁ and T₂­, and these values were then used to calculate contrast agent concentrations. The primary goal was to quantify two contrast agents residing in a mixed sample. The method  showed an accuracy  greater than 90% in most cases, indicating its feasibility. In addition,  the method was also able to quantify the bound and unbound state of a targeted contrast agent in near real-time.

Mayank V Jog¹, Robert X. Smith², Kay Jann², Walter Dunn³, Allan Wu², and Danny JJ Wang^2
1Biomedical Engineering, University of California Los Angeles, Los Angeles, CA, United States, ²Neurology, University of California Los Angeles, Los Angeles, CA, United States, ³Psychiatry, University of California Los Angeles, Los Angeles, CA, United States

Transcranial Direct Current Stimulation(tDCS) is a neuromodulation technique. Reported to improve clinical conditions as well as cognition, tDCS has potential as a treatment modality since it involves only simple scalp electrodes to drive mA currents. To date, only mathematical modeling has been used to visualize tDCS-applied currents.

 

In previous work, we used MRI field mapping in a novel paradigm to visualize in-vivo, a component of the magnetic field generated by these currents. The present work completes the picture by validating our current visualization technique via comparison between the measured and simulated current-induced fields in a specially constructed phantom.

Zhe Liu¹, Pascal Spincemaille², and Yi Wang^1,2
1Biomedical Engineering, Cornell University, Ithaca, NY, United States, ²Radiology, Weill Cornell Medical College, New York, NY, United States

The quality of Quantitative Susceptibility Mapping (QSM) depends critically on a correct estimation of total magnetic field, which may sometimes be degraded by phase unwrapping failure. We propose to bypass the traditional field estimation and phase unwrapping steps and estimate both background field and local susceptibility distribution directly from complex GRE images, which is referred to as dcQSM. Since no field is explicitly existent in our method, dcQSM eliminates phase unwrapping errors in tradition methods.

Woo Chul Jeong¹, Saurav ZK Sajib¹, Nitish Katoch¹, Bup Kyung Choi¹, Hyung Joong Kim¹, Oh In Kwon², and Eung Je Woo^1
1Kyung Hee University, Seoul, Korea, Republic of, ²Konkuk University, Seoul, Korea, Republic of

Electrical stimulations are widely used as therapeutic techniques that are closely related to the electromagnetic fields inside the human body. The electromagnetic field is affected by the injected currents and electrical conductivities of biological tissue, the map of voltage, current density, and magnetic flux density can provide meaningful information for determining the tissue type and current pathways. The signal intensity of current density is proportional to magnetic flux density which can be measured by MREIT. Since the biological tissues show anisotropic characteristic, we introduced a recent DT-MREIT method to better apply it to real situation.

YP Liao¹, A.-M. Oros-Peusquens¹, J. Lindemeyer¹, N. Lechea¹, C. Weiss², G. Stoffels¹, C. Filss¹, K.J. Langen¹, and N.J. Shah^1,3
1Institute of Neuroscience and Medicine-4, Forschungszentrum Juelich, Juelich, Germany, ²Department of Neurosurgery, University of Cologne, Cologne, Germany, ³Department of Neurology, JARA, Faculty of Medicine, RWTH Aachen University, Aachen, Germany

The availability of combined MR-PET scanners opens new opportunities for the characterisation of the tumour environments. In this study, MR-based simultaneous water content, electrical conductivity and susceptibility mapping in meningioma patients was implemented based on a multi-echo gradient echo sequence. The information was complemented by characterisation of the tumour with simultaneous FET-PET. This is a powerful combination of parameters which reflect important aspects of tissue physiology and also characterise to a large extent, tumour electromagnetic (EM) properties. This multi-parametric information helps to understand pathological tissue and can be applied to planning nonionizing EM hyperthermia therapy.

Kathleen M Ropella¹ and Douglas C Noll^1
1Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States

The use of multi-channel receivers is essential for acquiring B₁⁺ with sufficient SNR to calculate electrical properties. Combining the individual channel images prior to these calculations typically involves a SENSE-like method or the use of some reference image. In this work we present a modified version of coil compression to provide an automatic and simplified multi-channel array data combination for high SNR phase-based conductivity mapping. 

Sung-Min Gho¹, Jaewook Shin¹, Min-Oh Kim¹, Min Jung Kim², Sooyeon Kim², Jun-Hyeong Kim¹, and Dong-Hyun Kim^1
1School of Electrical and Electronic Engineering, Yonsei University, Seoul, Korea, Republic of, ²Department of Radiology, Yonsei University College of Medicine, Seoul, Korea, Republic of

Electric conductivity and apparent diffusion coefficient (ADC) give meaningful information to the clinicians and researchers, however, studies related to the relationship of these two phenomena were not substantially proceeded.

In this abstract, we observe the correlation between electrical conductivity and ADC under various situations (i.e. phantom, in vivo brain, and breast tumor case).

Shi Su¹, Yanan Ren¹, Caiyun Shi¹, Xiaoyong Zhang^1,2, Hairong Zheng¹, Xin Liu¹, and Guoxi Xie^1
1Lauterbur Research Center for Biomedical Imaging, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China, People's Republic of, ²Centers for Biomedical Engineering, College of Information Science and Technology, University of Science and Technology of China, Hefei, China, People's Republic of

T2* mapping provides a means to quantitatively estimate the iron load of tissue, which is closely related to numerous diseases, such as thalassemia, hereditary hemochromatosis and sickle cell disease. However, blood signal would induce artifacts which lead to T2* estimation inaccurate. To address this issue, a novel black-blood T2* mapping technique utilizing Delay Alternating with Nutation for Tailored Excitation (DANTE) preparation module followed by multi-echo gradient echo (GRE) readout (DANTE-GRE) was developed to obtain blood suppressed T2* maps. The proposed method is shown to acquire more accurate T2* maps due to its high SNR and effective blood signal suppression.

Saurav ZK Sajib¹, Woo Chul Jeong¹, Nitish Katoch¹, Bup Kyung Choi¹, Hyung Joong Kim¹, Oh In Kwon², and Eung Je Woo^1
1Kyung Hee University, Seoul, Korea, Republic of, ²Konkuk University, Seoul, Korea, Republic of

Quantitative visualization of induced current density by the electrical stimulation current inside the anisotropic brain region may play an important role to understand the neuro-modulatory effect during transcranial direct current stimulation (tDCS). For ensuring the clinical applications, precise approaches are required to understand the exact responses inside the human body subject to an injected currents, In this study, we reconstruct current density distribution inside the in vivo canine brain region by combing the directional information obtained from a DTI-MRI scan and the z-component of the magnetic flux density data using MREIT technique.