he term MR angiography comprises a number of different MR-based techniques that image flowing blood. Thin slices are acquired through the blood vessels that can be viewed directly or, more commonly, in angiographic format using a maximum intensity projection (MIP) algorithm. In addition, several of the techniques are sensitive to the direction of flowing blood and thus can distinguish veins and arteries. MR angiography can be performed with or without gadolinium. With the newest class of echo-planar MR imaging systems, first pass, gadolinium-enhanced MRA is rapidly becoming the imaging procedure of choice for all arterial imaging outside the brain.