Brain blood vessels. Coloured magnetic resonance angiography (MRA) scan showing healthy blood vessels (white) supplying a human brain (orange). The front of the head is at top, showing the nose (blue). MRA is a magnetic resonance imaging (MRI) technique that highlights blood vessels without needing to inject the radio-opaque dye that is used for X-ray angiography. It provides clear images of the brain's vascular system in order to determine if there are any abnormalities, such as stenoses (vessel narrowing) and aneurysms (blood collections caused by weakened vessel walls).