Diffusion of myelin water

We studied compartmentally specific characteristics of water diffusion in excised frog sciatic nerve by combining T-1 or T-2 selective acquisitions with pulse-gradient spin-echo (PGSE) diffusion weighting, with the specific objective of characterizing myelin water diffusion. Combining a PGSE with a Carr-Purcell-Meiboom-Gill (CPMG) acquisition provided apparent diffusion coefficients (ADCs) for each of the three T-2 components found in nerve, including the short-lived component believed to be derived from myelin water. Double-inversion-recovery (DIR) preparation provided an alternate means of discriminating myelin water, and in combination with PGSE provided somewhat different measures of ADC. The DIR measures yielded myelin water ADCs of 0.37 mu m(2)/ms (parallel to nerve) and 0.13 mu m(2)/ms (perpendicular to nerve). These ADC estimates were postulated to be more accurate than those based on T-2 discrimination, although the difference between the two findings is not clear.