MR angiography: noninvasive vascular imaging of the abdomen.

Magnetic resonance angiography (MRA) has been used to image abdominal vessels less frequently than renal arteries. Until the use of fast contrast-enhanced (CE) techniques, an important limitation was the acquisition time of phase-contrast or time-of-flight imaging and, consequently, the creation of motion artifacts. Recent advances in MRA technology have shortened acquisition times, so it is now possible to obtain successive images in the arterial and then the portal phase. MRA can be used as an adjunct to any MR examination to assess, e.g., the arterial feeding of hepatocellular carcinoma, the encasement of arteries, and segmental portal thrombosis in pancreatic carcinoma. However, MRA has been used mainly to study chronic mesenteric ischemia, portal vein diseases, and complications from liver transplantation. The portal venous system is exquisitely portrayed with this method; MRA is as accurate as digital subtraction angiography (DSA) in the diagnosis of portal vein diseases. Acute mesenteric ischemia is an emergency in which computed tomography is the most appropriate imaging modality. Conversely, chronic mesenteric ischemia is best examined with CE-MRA, which is almost as accurate as DSA. CE-MRA is superior to DSA for the simultaneous exploration of the aorta, renal arteries, and iliac arteries, thereby providing a panoramic view of abdominal vascular involvement. MRA can be coupled with measurements of flow. With this functional approach, MRA is the only modality that can completely assess vascular diseases of the abdomen.