Simultaneous measurement of total water content and myelin water fraction in brain at 3T using a T 2 relaxation based method.

PURPOSE: This work demonstrates the in vivo application of a T2 relaxation based total water content (TWC) measurement technique at 3T in healthy human brain, and evaluates accuracy using simulations that model brain tissue. The benefit of using T2 relaxation is that it provides simultaneous measurements of myelin water fraction, which correlates to myelin content.

METHODS: T2 relaxation data was collected from 10 healthy human subjects with a gradient and spin echo (GRASE) sequence, along with inversion recovery for T1 mapping. Voxel-wise T2 distributions were calculated by fitting the T2 relaxation data with a non-negative least squares algorithm incorporating B1 + inhomogeneity corrections. TWC was the sum of the signals in the T2 distribution, corrected for T1 relaxation and receiver coil inhomogeneity, relative to either an external water standard or cerebrospinal fluid (CSF). Simulations were performed to determine theoretical errors in TWC.

RESULTS: TWC values measured in healthy human brain relative to both external and CSF standards agreed with literature values. Simulations demonstrated that TWC could be measured to within 3-4% accuracy.

CONCLUSION: In vivo TWC measurement using T2 relaxation at 3T works well and provides a valuable tool for studying neurological diseases with both myelin and water changes.