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. Magn Reson Med 61:883-892, 2009. (C) 2009 Wiley-Liss, Inc.