Fast multislice mapping of the myelin water fraction using multicompartment analysis of T₂* decay at 3T: A preliminary postmortem study

Quantitative mapping of the myelin water content can provide significant insight into the pathophysiology of several white matter diseases, such as multiple sclerosis and leukoencephalopathies, and can potentially become a useful clinical tool for early diagnosis of these diseases. In this study, multicompartment analysis of T₂* decay (MCAT2*) was used for the quantitative mapping of myelin water fraction (MWF). T ₂* decay of each voxel at multiple slice locations was acquired in fixed human brains using a multigradient-echo (MGRE) pulse sequence with alternating readout gradient polarities. Compared to prior techniques using Carr-Purcell-Meiboom-Gill (CPMG) acquisition, the MGRE acquisition approach has: 1) a very short first echo time (≈2 ms) and echo-spacing (≈1 ms), which allows for the acquisition of multiple sampling points during the fast decay of the myelin water signal; 2) a low RF duty cycle, which is especially important for achieving acceptable specific absorption rate (SAR) levels at high field strengths. Multicompartment analysis was then applied to the T ₂* decay in each pixel using a 3-pool model of white matter to detect the signal arising from the myelin water, myelinated axonal water, and mixed water compartments.