The physical basis of diffusion-weighted MRI.

Diffusion-weighted (DW) magnetic resonance imaging (MRI) is the only technique that permits a non-invasive in vivo assessment of water molecular diffusion, which reflects tissue configuration at a microscopic level. Therefore, this technique appears to be particularly useful in monitoring brain abnormalities. However, the quantitative measurement of diffusion is not without problems, which may limit the widespread use of diffusion-weighted MRI. In this report, the phenomenon of diffusion is described, together with its effect on the nuclear magnetic resonance signal. The concepts of diffusion anisotropy and diffusion tensor are also introduced, and the technical and hardware requirements are discussed.