Multi-component apparent diffusion coefficients in human brain: Relationship to spin-lattice relaxation

In vivo measurements of the human brain tissue water signal decay with b-fa ctor over an extended b-factor range up to 6,000 s/mm(2) reveal a nonmonoex ponential decay behavior for both gray and white matter. Biexponential para metrization of the decay curves from cortical gray (CG) and white matter vo xels from the internal capsule (IC) of healthy adult volunteers describes t he decay process and serves to differentiate between these two tissues. Inv ersion recovery experiments performed in conjunction with the extended b-fa ctor signal decay measurements are used to make separate measurements of th e spin-lattice relaxation times of the fast and slow apparent diffusion coe fficient (ADC) components. Differences between the spin-lattice relaxation times of the fast and slow ADC components were not statistically significan t in either the cc or IC voxels, It is possible that the two ADC components observed from the extended b-factor measurements arise from two distinct w ater compartments with different intrinsic diffusion coefficients. If so, t hen the relaxation results are consistent with two possibilities. Either th e spin-lattice relaxation times within the compartments are similar or the rate of water exchange between compartments is "fast" enough to ensure volu me averaged T-1 relaxation yet "slow" enough to allow for the observation o f biexponential ADC decay curves over an extended b-factor range. Magn Reso n Med 44:292-300, 2000, (C) 2000 Wiley-Liss, Inc.