Non-invasive assessment of renal artery stenosis: Current concepts and future directions in magnetic resonance angiography

Magnetic resonance angiography is undergoing rapid development as a non-inv asive technique to reliably assess renal artery stenosis. Invasive X-ray an giography is currently the gold standard imaging technique and gives excell ent spatial resolution. However, its;disadvantages include a necessary expo sure to radiation and the need for iodinated contrast media. While magnetic resonance angiography does not have these disadvantages, its spatial resol ution is inherently lower. On the other hand, magnetic resonance angiograph y enables true three-dimensional imaging. The use of rapid imaging techniqu es allows multiple image acquisition within one breath-hold thereby permitt ing the visualization of distinct vascular phases. The limitation in spatia l resolution can be overcome readily by combining morphologic imaging with functional information on the hemodynamic relevance. This can be achieved b y means of magnetic resonance phase contrast flow measurements. The use of such a combined approach enables the grading of vascular stenosis based on the combination of morphology and functional information. Magnetic resonanc e angiography is already able to demonstrate a clinical utility equivalent to that of invasive procedures, indicating that it is likely to become a pr emier method for the diagnosis and follow up of renovascular disease.