Isolating restriction and exchange in gray matter using double and single diffusion encodings with equal diffusion weighting
Teddy Xuke Cai1,2, Nathan Hu Williamson2,3, Rea Ravin2,4, and Peter Joel Basser2
1Department of Clinical Neurosciences, Wellcome Centre for Integrative Neuroimaging, FMRIB, University of Oxford, Oxford, UK, United Kingdom, 2Section on Quantitative Imaging and Tissue Sciences, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, MD, United States, 3National Institute of General Medical Sciences, Bethesda, MD, United States, 4Celoptics, Inc., Rockville, MD, United States
The diffusion MR signal in complex tissue such as gray matter exhibits non-Gaussian signal attenuation due to exchange and restrictions. Existing signal models typically ignore one or both effects by assuming Gaussian diffusion or negligible exchange. We propose a more rigorous signal model that incorporates both effects. Subsequently, an acquisition scheme utilizing equal double diffusion encodings ($$$b_1=b_2$$$) at various mixing times, and single diffusion encodings with the same total weighting $$$b=b_1+b_2$$$, is designed to independently characterize the effects of restriction and exchange. The method is tested on live and fixed gray matter specimen using a low-field, high-gradient MR system.
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