Magnetic Resonance Angiography (MRA)
Magnetic resonance angiography (MRA) is a group of techniques based on magnetic resonance imaging to demonstrate blood vessels, looking for evidence of stenosis, occlusion, or aneurysm formation. Demonstration of abnormalities in the vena cava in patients with large renal cancers is a particular urological use. The principle of MRA is to acquire images depicting areas where the signal returned from flowing nuclei is high and the signal from stationary nuclei is low. In this way, the contrast between vessels and background tissue is obtained. The two principle types of MRA are time-of-flight and phase-contrast angiography.