Diffusion Pulse Sequences

Various pulse sequences may be modified to enhance signal loss resulting from water molecules that show significant diffusion vs those with more restricted diffusion. Certain pathology shows restriction of diffusion, such as cytotoxic edema and demyelinization. With a diffusion-weighted pulse sequence, these abnormalities can be made more obvious. Depending on the particular gradient/gradients used, anisotropic diffusion can be detected, as occurs normally in white matter tracts. The picture below is a spin echo sequence with diffusion gradients added. The gradient coil used to produce the diffusion need not be a separate gradient or gradients from those used for spatial encoding. The degree of diffusion weighting is dependent primarily on the area under the diffusion gradients and on the interval between the gradients. Other factors include the effect of the spatial localization gradients and the size of the voxels.