In vivo measurement of T-2 distributions and water contents in normal human brain

Using a 32-echo imaging pulse sequence, T-2 relaxation decay curves were acquired from five white- and six gray-matter brain structures outlined in 12 normal volunteers, The water contents of white and gray matter were 0.71 (0.01) and 0.83 (0.03) g/ml, respectively, All white-matter structures had significantly higher myelin water percentages (signal percentage with T-2 between 10 and 50 ms) than all gray-matter structures, The range in geometric mean T-2 of the main peak for both white and gray matter was from 70 to 86 ms, T-2 distributions from the posterior internal capsules and splenium of the corpus callosum were significantly wider (width is related to water environment inhomogeneity) than those from any other white- or gray-matter structures, Thus, quantitative measurement and analysis of T-2 relaxation reveals differences in brain tissue water environments not discernible on conventional MR images, These differences may make short T-2 components reliable markers for normal myelin.