Comparison of Myelin Water Fraction from Multiecho T2 Decay Curve and Steady-State Methods

PurposeMyelin water fraction is conventionally measured from the T-2 decay curve. Recently, a steady-state approach entitled multicomponent-driven equilibrium single pulse observation of T-1/T-2 (mcDESPOT) was employed for myelin water fraction mapping. However, no direct comparison between the established multiecho T-2 relaxation method and mcDESPOT has been performed. MethodsGradient and spin echo (GRASE) acquired T-2 decay curve and mcDESPOT measurements were acquired from 10 healthy volunteers using a 3T MRI. We compared myelin water fraction, transmit radio frequency field (B-1), and T-2's of intra- and extracellular water obtained from both methods. ResultsFor all brain regions examined, myelin water fractions from mcDESPOT were significantly higher than those from multiecho GRASE. B-1 maps were qualitatively similar between GRASE and mcDESPOT, but multicomponent T-2 times were significantly different. To investigate the effect of exchange, mcDESPOT data were analyzed with and without exchange. When exchange was turned off, intra- and extracellular T-2 times from mcDESPOT were roughly consistent with GRASE results; however, myelin water fractions derived from mcDESPOT were still significantly higher than those derived from GRASE. ConclusionMyelin water fraction values derived from mcDESPOT cannot be considered to be equivalent to those derived from T-2 decay curve approaches. Magn Reson Med 73:223-232, 2015. (c) 2014 Wiley Periodicals, Inc.