Ella Wilczynski1, Efrat Sasson2, Uzi Eliav2, Gil Navon2, Uri Nevo3,4. 1. Department of Biomedical Engineering, Faculty of Engineering, Tel Aviv University, Tel Aviv, Israel. 2. School of Chemistry, Faculty of Exact Sciences, Tel Aviv University, Tel Aviv, Israel. 3. Department of Biomedical Engineering, Faculty of Engineering, Tel Aviv University, Tel Aviv, Israel. nevouri@tauex.tau.ac.il. 4. Sagol School of Neuroscience, Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel. nevouri@tauex.tau.ac.il.
Abstract
OBJECTIVE: Magnetization EXchange (MEX) sequence measures a signal linearly dependent on the myelin proton fraction by selective suppression of water magnetization and a recovery period. Varying the recovery period enables extraction of the percentile fraction of myelin bound protons. We aim to demonstrate the MEX sequence sensitivity to the fraction of protons associated with myelin in mice brain, in vivo. METHODS: The cuprizone mouse model was used to manipulate the myelin content. Mice fed cuprizone (n = 15) and normal chow (n = 8) were imaged in vivo using MEX sequence. MR images were segmented into corpus callosum and internal capsule (white matter) and cortical gray matter, and fitted to the recovery equation. Results were analyzed with correlation to MWF and histopathology. RESULTS: The extracted parameters show significant differences in the corpus callosum between the cuprizone and control groups. The cuprizone group exhibited reduced myelin fraction 26.5% (P < 0.01). The gray matter values were less affected, with 13.5% reduction (P < 0.05); no changes were detected in the internal capsule. Results were validated by MWF scans and good correlation to the histology analysis (R2 = 0.685). CONCLUSION: The results of this first in vivo implementation of the MEX sequence provide a quantitative measure of demyelination in brain white matter.
OBJECTIVE: Magnetization EXchange (MEX) sequence measures a signal linearly dependent on the myelin proton fraction by selective suppression of water magnetization and a recovery period. Varying the recovery period enables extraction of the percentile fraction of myelin bound protons. We aim to demonstrate the MEX sequence sensitivity to the fraction of protons associated with myelin in mice brain, in vivo. METHODS: The cuprizone mouse model was used to manipulate the myelin content. Mice fed cuprizone (n = 15) and normal chow (n = 8) were imaged in vivo using MEX sequence. MR images were segmented into corpus callosum and internal capsule (white matter) and cortical gray matter, and fitted to the recovery equation. Results were analyzed with correlation to MWF and histopathology. RESULTS: The extracted parameters show significant differences in the corpus callosum between the cuprizone and control groups. The cuprizone group exhibited reduced myelin fraction 26.5% (P < 0.01). The gray matter values were less affected, with 13.5% reduction (P < 0.05); no changes were detected in the internal capsule. Results were validated by MWF scans and good correlation to the histology analysis (R2 = 0.685). CONCLUSION: The results of this first in vivo implementation of the MEX sequence provide a quantitative measure of demyelination in brain white matter.
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