Abstract: The invention provides a method of detecting blood flow abnormality or variation in a human or non-human body, said method comprising administering into the cardiovascular system of a said body a contrast enhancing amount of an intravascular paramagnetic metal containing magnetic resonance imaging contrast agent, subject said body to a magnetic resonance imaging procedure capable of generating from magnetic resonance signals from said body a series of temporally spaced images of at least a part of said body into which said agent passes, and detecting temporal variations in said signals or images whereby to identify regions of abnormal or modified blood flow in said body and to indicate the degree of blood flow abnormality or modification therein.