Magnetic resonance angiography of the kidney

Magnetic resonance angiography (MRA) of the kidneys has become a clinical standard for detecting renal artery stenosis. This test is performed by injecting a bolus of a gadolinium chelate and scanning with a three-dimensional volumetric data collection sensitized to the T1 shortening effects of gadolinium. In addition to displaying the renal arterial anatomy, atherosclerosis within the aorta and iliac arteries is commonly depicted. MRA is a time efficient and safe test when compared with conventional arteriography. Gadolinium-enhanced MRA has proven to have a high sensitivity for detecting stenoses in main and accessory renal arteries. Although false-negative studies are rare, overestimation of the degree of renal stenosis is problematic and may lead to false-positive diagnosis. To some extent this tendency to overestimate stenoses can be compensated for by performing phase contrast MRA, a type of MRA based on accumulated phase differences. As with conventional angiography, MRA is still only an anatomic test which provides little information about the functional significance of a stenosis. It is highly accurate in determining the number of renal arteries, the size of the kidneys, and the presence of any anatomic variants. Ultimately, MRA, needs to be combined with a functional test similar in concept to captopril renography. This test, termed MR renography together with MRA may replace the current multimodalitiy approach to the work-up of renovascular hypertension.