Practice question

Diffusion tensor imaging extends conventional MRI by sensitizing signal to microscopic random motion of water. In white matter, parallel axonal membranes and myelin sheaths restrict diffusion perpendicular to fibers while permitting relatively free movement along them, producing anisotropic diffusion ellipsoids. By measuring diffusion in at least six directions, tensor eigenvalues and eigenvectors are calculated, enabling color-coded fractional anisotropy maps and three-dimensional tractography of corticospinal tract, corpus callosum and arcuate fasciculus. CT lacks such contrast, fMRI shows activation, PET shows metabolism, none delineate fiber tracts.