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Microstructural changes in ischemic cortical gray matter predicted by a model of diffusion-weighted MRI

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PURPOSE: To understand the diffusion attenuated MR signal from normal and
ischemic brain tissue in order to extract structural and physiological
information using mathematical modeling, taking into account the transverse
relaxation rates in gray matter. MATERIALS AND METHODS: We fit our diffusion
model to the diffusion-weighted MR signal obtained from cortical gray matter in
healthy subjects. Our model includes variable volume fractions, intracellular
restriction effects, and exchange between compartments in addition to individual
diffusion coefficients and transverse relaxation rates for each compartment. A
global optimum was found from a wide range of parameter permutations using
cluster computing. We also present simulations of cell swelling and changes of
exchange rate and intracellular diffusion as possible cellular mechanisms in
ischemia. RESULTS: Our model estimates an extracellular volume fraction of 0.19
in accordance with the accepted value from histology. The absolute apparent
diffusion coefficient obtained from the model was similar to that of experiments.
The model and the experimental results indicate significant differences in
diffusion and transverse relaxation between the tissue compartments and slow
water exchange. Our model reproduces the signal changes observed in ischemia via
physiologically credible mechanisms. CONCLUSION: Our modeling suggests that
transverse relaxation has a profound influence on the diffusion attenuated MR
signal. Our simulations indicate cell swelling as the primary cause of the
diffusion changes seen in the acute phase of brain ischemia.
Original languageEnglish
JournalJournal of Magnetic Resonance Imaging
Pages (from-to)529-40
Number of pages12
Publication statusPublished - 2007

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