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

PURPOSE

This work demonstrates the in vivo application of a T 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 T relaxation is that it provides simultaneous measurements of myelin water fraction, which correlates to myelin content.

METHODS

T relaxation data was collected from 10 healthy human subjects with a gradient and spin echo (GRASE) sequence, along with inversion recovery for T mapping. Voxel-wise T distributions were calculated by fitting the T relaxation data with a non-negative least squares algorithm incorporating B inhomogeneity corrections. TWC was the sum of the signals in the T distribution, corrected for T 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 T relaxation at 3T works well and provides a valuable tool for studying neurological diseases with both myelin and water changes.