Myelin water measurement in the spinal cord.

The desire to monitor the spatial-temporal characteristics of myelination in the spinal cord (SC), in the context of pathological change in demyelinating diseases or proposed neuroregenerative protocols, has led to an interest in noninvasive image-based myelin measurement methods. We present one strategy: a magnetic resonance-based measure that capitalizes on the characteristics of T(2) relaxation of water compartmentalized within tissue. In this study, 32-echo relaxation studies for measuring the myelin water fraction (MWF) were applied in healthy control SC in vivo using a sagittal inversion recovery multiecho sequence, and findings were supported with supplemental studies in bovine SC samples in vitro. Mean human MWF varied according the level of the SC examined: cervical, thoracic, and lumbar MWF was found to be 21.8 (SD=2.1)%, 24.3 (3.6)%, and 11.4 (6.4)%, respectively. Noteworthy reductions were observed in areas consistent with the expected locations of the cervical and lumbar enlargements. Average bovine MWF was 30.0 (2.7)% in white matter and 8.2 (0.4)% in gray matter. The potential applications of T(2) measurement in SC, both in characterizing disease processes like multiple sclerosis and in monitoring neuroregenerative therapies, should encourage future research in this area.