Evgeniya Kirilina^1,2, Ilona Lipp¹, Carsten Jäger¹, Markus Morawski³, Merve N. Terzi^4,5, Hans-Jürgen Bidmon⁶, Markus Axer⁴, Pitter F. Huesgen⁵, and Nikolaus Weiskopf^1,7,8
1Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany, ²Center for Computational Neuroscience, Free University Berlin, Berlin, Germany, ³Paul Flechsig Institute of Brain Research, University of Leipzig, Leipzig, Germany, ⁴Institute of Neuroscience and Medicine, Forschungszentrum Jülich, Juelich, Germany, ⁵Zentralinstitut für Engineering, Elektronik und Analytik, Forschungszentrum Jülich, Juelich, Germany, ⁶C. und O. Vogt-Instituts für Hirnforschung, Heinrich-Heine-Universität Düsseldorf, Duesseldorf, Germany, ⁷Felix Bloch Institute for Solid State Physics, Leipzig University, Leipzig, Germany, ⁸Wellcome Centre for Human Neuroimaging, University College London, London, United Kingdom

Quantitative MRI parameters in the brain provide unique information on tissue myelination. However, the validation studies performing quantitative comparisons between MRI metrics and tissue myelin content are very limited, mainly due to the to the lack of methods for histological myelin quantification. Here, we explore lipid imaging using matrix-assisted laser desorption/ionization (MALDI) and multiple histological myelin stains in post-mortem human brain tissue samples for validation of MRI based myelin biomarkers. We show that tissue lipid composition vary across different cortical layers and white matter pathways, potentially reflecting differences in myelin structure and may impact MRI-based myelination metrics.

Ronja Berg¹, Aurore Menegaux¹, Guillaume Gilbert², Claus Zimmer¹, Christian Sorg¹, Irene Vavasour³, and Christine Preibisch^1
1School of Medicine, Department of Neuroradiology, Technical University of Munich, Munich, Germany, ²MR Clinical Science, Philips Healthcare, Markham, ON, Canada, ³Radiology, University of British Columbia, Vancouver, BC, Canada

Microstructural parameters of the brain such as the myelin concentration or g-ratio (average ratio between axonal and fiber diameter) can provide important information on the pathophysiology of demyelinating diseases. Several myelin sensitive MRI methods exist. However, correlations between different myelin sensitive measures and the best choice for g-ratio mapping is not yet fully explored. Therefore, we compared MWF, ihMTR, and MTsat in white matter and found the highest correlation between MWF and ihMTR. Those measures also varied more strongly across WM regions compared to MTsat, which suggests that they could be more reliable for further analyses such as g-ratio imaging.

Michelle H Lam^1,2, Valentin H Prevost², Andrew Yung², and Piotr Kozlowski^1,2,3,4
1Physics, University of British Columbia, Vancouver, BC, Canada, ²UBC MRI Research Centre, University of British Columbia, Vancouver, BC, Canada, ³Radiology, University of British Columbia, Vancouver, BC, Canada, ⁴International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, BC, Canada

Inhomogeneous magnetization transfer (ihMT) is a novel MR imaging technique that could be used for myelin-specific imaging if the sequence is properly tuned to filter components with short  dipolar relaxation time (T_1D). It is believed that ihMT’s dependence on T_1D serves as a method to extract the myelin-related signal, due to its longest dipolar order among the brain structures. Here, we have combined two myelin imaging techniques, ihMT and myelin water imaging (MWI), to study myelin and intra-/extra-cellular water’s contribution to the overall ihMT signal.

Peng Cao¹, Di Cui¹, Queenie Chan², and Edward S. Hui^1
1Diagnostic Radiology, The University of Hong Kong, Hong Kong, China, ²Philips Healthcare, Hong Kong, China

We proposed a new multi-inversion-recovery (mIR) myelin water mapping (MWF)-MRF sequence that allows 24 s/slice scan speed for four-compartment (myelin water, cerebrospinal fluid, gray matter and white matter) brain mapping on clinical 3T MRI.

Yajun Ma¹, Hyungseok Jang¹, Zhao Wei¹, Zhenyu Cai¹, Yanping Xue¹, Eric Y Chang², Jody Corey-Bloom¹, and Jiang Du^1
1UC San Diego, San Diego, CA, United States, ²VA health system, San Diego, CA, United States

To quantitatively image myelin on clinical scanners, we propose a Short TR Adiabatic Inversion Recovery prepared UTE (STAIR-UTE) sequence for in vivo brain imaging. With STAIR technique, long T2 tissues with a broad range of T1s can be sufficiently suppressed. Healthy volunteer has a higher myelin proton density in white matter than that in patient with multiple sclerosis.  

Kwok-Shing Chan¹, Renaud Hedouin¹, and José P. Marques^1
1Donders Institute for Brain, Cognition and Behaviour, Radboud University, Nijmegen, Netherlands

In this study, we propose an extension of the formalism of gradient echo based myelin water imaging by incorporating diffusion-weighted imaging data and an analytical white matter fibre model of signal evolution in a hollow cylinder. Voxel-wise analysis illustrated that the proposed model can significantly reduce the noise in the MWF estimation compared to the standard model, providing robust estimation even on high resolution data.

Jieun Lee¹, Joon Yul Choi², Dongmyung Shin¹, Se-Hong Oh³, and Jongho Lee^1
1Department of Electrical and Computer Engineering, Seoul National University, Seoul, Korea, Republic of, ²Cleveland Clinic, Epilepsy Center, Neurological Institute, Cleveland, OH, United States, ³Division of Biomedical Engineering, Hankuk University of Foreign Studies, Gyeonggi-do, Republic of Korea

In this study, the generalization capacity of the artificial neural network for myelin water imaging (ANN-MWI) is explored by testing datasets with different (1) scan protocols (resolution, RF shape, and TE), (2) noise levels, and (3) types of disorders (NMO and edema). The ANN-MWI results show high reliability in generating myelin water fraction maps from the datasets with different resolution and noise levels. However, the increased errors are reported for the datasets with the different RF shape, TEs, and disorder type.

Christoph Birkl^1,2, Jonathan Doucette^1,3, Enedino Hernández-Torres¹, and Alexander Rauscher^1,3,4
1UBC MRI Research Centre, University of British Columbia, Vancouver, BC, Canada, ²Department of Neurology, Medical University of Graz, Graz, Austria, ³Department of Physics & Astronomy, University of British Columbia, Vancouver, BC, Canada, ⁴Department of Pediatrics (Division of Neurology), University of British Columbia, Vancouver, BC, Canada

We demonstrated that the measurement of MWF is considerably influenced by the angle between the white matter fiber tracts and the main magnetic field. Furthermore, we showed that the traditionally used cut-off between myelin water and intra- and extracellular water of 40 ms overestimates MWF.

JP Galons¹, Kevin Harkins², Mark Does², Theodore Trouard¹, and Elizabeth Hutchinson^1
1University of Arizona, Tucson, AZ, United States, ²Vanderbilt University, Nashville, TN, United States

MRI tools for mapping myelin content could provide useful markers of injury and repair in neurologic disorders that preferentially affect white matter such as traumatic brain injury (TBI).  In this study, we apply two novel myelin water mapping approaches - bound pool fraction (BPF) from selective inversion recovery MRI and myelin water fraction (MWF) from multiple spin echo MRI - in the ex-vivo ferret brain with and without injury in order to develop these myelin mapping markers for pre-clinical TBI research. We demonstrate high quality BPF and MWF maps and describe metric behavior in a region of focal injury.

Joon Yul Choi¹, John Whyte², Amanda R Rabinowitz², Vincent L Chow³, Se-Hong Oh⁴, Jongho Lee⁵, and Junghoon J Kim^3
1Epilepsy Center / Neurological Institute, Cleveland Clinic, Cleveland, OH, United States, ²Moss Rehabilitation Research Institute, Elkins Park, PA, United States, ³Department of Molecular, Cellular, and Biomedical Sciences, CUNY School of Medicine, The City College of New York, New York, NY, United States, ⁴Division of Biomedical Engineering, Hankuk University of Foreign Studies, Yongin, Korea, Republic of, ⁵Laboratory for Imaging Science and Technology, Department of Electrical and Computer Engineering, Institute of Engineering Research, Seoul National University, Seoul, Korea, Republic of

Reliable MRI biomarkers of white matter degeneration can be useful for monitoring post-traumatic progressive neurodegeneration and identifying potential treatment targets. We report that myelin water signal can be measured reliably during the first year after moderate to severe traumatic axonal injury. We also report that apparent myelin water fraction from the whole brain white matter continued to decrease beyond 3 months post-injury, reflecting progressive axonal degeneration and demyelination.