Diffusion-weighted imaging in the abdomen and pelvis: concepts and applications.

Diffusion-weighted magnetic resonance (MR) imaging allows the detection of focal solid and cystic lesions in the abdomen and pelvis and, if pitfalls are to be avoided, is most effectively used in conjunction with other imaging sequences. It is important to recognize that the strength of the diffusion sensitizing gradient (b value) can and should be adjusted to ensure optimal evaluation of the body region or organ being imaged, and that more than one b value is necessary for tissue characterization. The success of lesion detection and characterization largely depends on the extent of tissue cellularity because increased cellularity is associated with impeded diffusion, as indicated by a reduction in the apparent diffusion coefficient. It is also important to recognize that certain normal tissues such as the endometrium are highly cellular and as such demonstrate restricted diffusion, which should not be misinterpreted as disease. Impeded diffusion can also be seen in highly viscous cystic lesions such as abscesses. Diffusion-weighted imaging is an evolving technology with the potential to improve tissue characterization when findings are interpreted in conjunction with findings obtained with other conventional MR imaging sequences.