Measuring intra-axonal T2 in white matter with direction-averaged diffusion MRI.

摘要: Purpose To demonstrate how the T2 relaxation time of intra-axonal water (T2a ) in white matter can be measured with direction-averaged diffusion MRI. Methods For b-values larger than about 4000 s/mm2 , MRI signal from is dominated by contribution within axons, which enables T2a to estimated acquiring data for multiple TE values and fitting a mono-exponential decay curve. If given value diffusivity, an extension method allows extra-axonal (T2e calculated also. This approach was applied estimate 3 healthy subjects at T, as well T2e selected set assumed diffusivities. Results The ranged 50 ms 110 ms, considerable variation among regions. tracts primarily collinear fibers, found depend on angle tract relative main magnetic field, consistent being affected field inhomogeneities arising spatial differences susceptibility. were significantly smaller across regions several plausible choices diffusivity. Conclusion determined straightforward manner measuring large b-value TEs. In brain, greater varies considerably anatomical region.