An in vivo implementation of the MEX MRI for myelin fraction of mice brain

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 (R-2 = 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.

Automated summary

The study demonstrated the sensitivity of the MEX sequence to the fraction of protons associated with myelin in the mouse brain, with significant differences observed between the cuprizone and control groups in the corpus callosum and gray matter. This provides a quantitative measure for demyelination in brain white matter.