MR angiography of run-off vessels

Magnetic resonance angiography has taken a huge step forward since the intr oduction of contrast-enhanced MR angiography using gadolinium chelates. The more conventional MR angiographic techniques, such as time-of-flight and p hase-contrast MR angiography, have been ousted by contrast-enhanced MR angi ography in most vascular areas. However, in imaging the lower extremities, the major obstacle is the length of the vascular tree. In order to cover th e entire peripheral vasculature, at least two to three fields of view are r equired. Using contrast-enhanced MR angiography, the best results are obtai ned if the vessels of interest are imaged during passage sage of a bolus of contrast material. Vessel-to-background contrast in subsequent acquisition s using subsequent injections of contrast material is hampered by recircula tion and leakage of previously injected gadolinium, enhancing both the veno us system and surrounding tissue. To overcome this problem several research groups have come up with various solutions. The three main strategies empl oyed can be classified as either bolus catch, bolus chase, or bolus track t echniques. The purpose of this article is to explain working mechanisms of the three bolus imaging strategies for imaging both inflow and outflow vess els of the lower extremities, to show their advantages and disadvantages, a nd to review results described in the literature in imaging patients using these techniques.