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Major clinical challenges are involved in applications of MR-angiography for the study of renal arteries, mostly for the diagnosis of renovascular hypertension. This technique now competes with color Doppler flow sonography and spiral CT. MR angiography of the renal arteries can be performed with 2D or 3D, flight-time or phase contrast sequences. Main and co-dominant arteries are usual by visualized on all sequences, but small accessory arteries are often missed. The diagnosis of stenosis is based on the presence of an area of signal extinction. The degree of extinction depends on the degree of turbulence, the type of technique, the length of TE and spatial resolution parameters, which is why scoring of stenoses is difficult and frequently overestimated. The diagnostic performance for stenosis is between 50 and 100% for sensitivity and between 80 and 97% for specificity. Detection of distal stenoses is poor because of respiratory artifacts. Multiphase acquisitions make it possible to measure the renal blood flow on each renal artery, adding hemodynamic criteria to this diagnosis.

Ten normal rabbits and seven rabbits with experimental acute renal failure by tubular necrosis were studied with dynamic MR to evaluate the reproducibility of intrarenal kinetics of Gd-DOTA. Sequential spin-echo sequences with short TR (200 msec)/TE (26 msec) were used yielding a 29 sec acquisition time. A usual semi-quantitative analysis of intrarenal contrast demonstrated the reproducibility of some phases of the dynamic sequence in particular a drop in the signal within inner medulla between the third and the fourth minute after infusion. This effect, related to a high concentration of Gd-DOTA within the tubules was observed in 9 over 10 normal rabbits and in none of the rabbits with acute renal failure. The quantitative analysis calculation was based on relative signal intensity and contrast-to-noise ratio from the absolute signal intensity measure on regions-of-interest (ROI) on the cortex, outer medulla and inner medulla. No reproducibility of the variations with time of these parameters could be assessed. A great number of factors of variations or error, mainly during the measurements of signal intensity with ROI, could explain this lack of reproducibility. At the present, dynamic MR is therefore not able to quantitatively evaluate the renal function. Only a semi-quantitative estimation of tubular concentration can be deduced.