High-Resolution contrast-enhanced MR Angiography of the kidneys at 3 Tesla: Initial results

Purpose: Magnetic resonance angiography (MRA) is gaining increased acceptance as a reliable test for the detection of renal artery stenosis (RAS). Purpose of this study was the evaluation of a high-resolution MRA of the kidneys at 3.0T in healthy volunteers and patients with suspected RAS.

Methods: 15 healthy volunteers and 10 consecutive patients suspected of having RAS (17male, 8female, mean age 47.3 years) were scanned with a 3D-GRE Flash-sequence (TR/TE 2.9/1.2ms, flip 23°, matrix 576×432, voxel size 0.6×0.9×1.2mm³, GRAPPA 2, acquisition time 22s). Using an eight-channel phased-array surface coil on a 3.0T whole body scanner (Magnetom Trio, Siemens medical solutions) a high-resolution MRA in coronal projection was implemented in breath-hold with injection of 26ml gadodiamide (Omniscan, Amersham Health Inc.) at a rate of 2ml/s followed by 25ml of saline. For qualitative assessment unsubtracted and subtracted data sets were selected, coronal thin MIP images were prepared and reviewed throughout volume. Images were assessed subjectively on a 0–3 scoring scale based on visibility and delineation of vessels wall and image quality. Visibility and sharpness of renal arteries (RA), accessory RA, and delineation of RA branching and early venous enhancement were recorded. Quantitative evaluation was done by measuring the Contrast-to-Noise ratio (CNR) and Signal-to-Noise ratio (SNR) for abdominal aorta, and right and left RA.

Results: All studies were performed safely and without complication. Our technique was able to visualize RA in all subjects (100%) with mean visibility score of 2.3±0.3. RA were identified up to the second order branches in all subjects. In 4/10 patients a haemodynamic relevant narrowing of the RA was found and proven by conventional angiogram. No motion degradation of the RA manifest by blurring and reduction of arterial signal intensity (SI) were found. In 6/25 examinations an early venous enhancement was found without disturbing the diagnostic quality. Mean CNR of the aorta was 45.4±19.2, right RA 44.3±16.9, left RA 44.4±17.1.

Conclusion: Renal artery CEMRA at 3.0 T is feasible and the results are promising. Signal gain at 3.0 T imaging is an important factor to further increase spatial resolution and improves the visualization of small vessel segments. Additional information like accessory RA or pathology within the renal parenchyma or the urinary collecting system can be found.