Direct measurements of myelin T1 in ex-vivo brain white matter

Motivation: Estimates of T1 in white matter are significantly affected by magnetization transfer between macromolecular and aqueous protons. To fully resolve this interaction, the MR properties of the macromolecular pool must be better understood. Goal(s): Directly map the T1 relaxation times of nonaqueous proton signal components in white matter. Approach: Short-T2 methodology and hardware were employed to access the rapidly decaying signals from myelin and non-myelin macromolecules. T1 estimates were obtained for deuterated and untreated brain samples using the variable flip angle method. Results: The T1's of myelin and non-myelin macromolecules were found to be significantly shorter than those of aqueous white matter signals. Impact: In agreement with indirect approaches, this work challenges the common approximation that T1≈1s for the macromolecular pool. Direct T1 mapping of macromolecular proton pools in deuterated and untreated tissue opens new avenues to explore magnetization transfer interactions in white matter.