MR angiography of the portal venous system: techniques, interpretation, and clinical applications.

Magnetic resonance (MR) angiography is a noninvasive means of assessing the portal venous system that has potential advantages over currently used modalities. Time-of-flight and phase-contrast MR angiography are useful techniques that differ fundamentally in their means of data acquisition but are comparable in their ability to demonstrate normal anatomy as well as abnormalities of the portal venous system. Occasionally, artifacts caused by respiratory motion, implanted metallic devices or surgical clips, in-plane saturation, or areas of complex flow are seen at MR angiography of the portal venous system. However, most artifacts can easily be identified as such and either remedied or ignored. In addition, the suppression of signal from surrounding soft tissues may result in poor detection of parenchymal lesions. The utility of standard projection angiograms and source images can be increased through the use of intravenously administered contrast material and postprocessing techniques such as partial-volume maximum intensity projection reconstructions and shaded surface renderings. In addition to providing information on portal venous anatomy and portosystemic collateral vessels, MR angiography of the portal vein has clinical application in portal venous thrombosis and stenosis, liver transplantation, and the evaluation and planning of surgical and transjugular intrahepatic portosystemic shunts.