Excluding Renal Artery Stenosis Using 3.0-T MRA

A recent study was conducted to assess the accuracy of 3.0-T contrast-enhanced MR angiography (MRA) in evaluating patients with arterial hypertension and suspected renal artery stenosis.

This prospective analysis was comprised of 29 patients. The results indicate that contrast-enhanced 3.0-T MR angiography is reliable in excluding renal artery stenosis.

Methods
Examinations were performed with a 3.0-Tesla system using parallel imaging techniques and a phased array surface coil. Three-dimensional T1-weighted gradient echo MRA volume was obtained in the coronal plane.

Multiplanar reconstructions in axial and sagittal planes or sub-volume maximum intensity projections were generated from original data.

Fifteen patients also had a digital subtraction angiogram.

MRA and digital subtraction angiographic images were independently reviewed by 2 MR radiologists.

The degree of renal artery stenosis was confirmed in 2 projections and graded as follows:

• normal (grade 0);
• mild (grade 1 or 1% to 49%);
• moderate (grade 2 or 50% to 75%);
• severe (grade 3 or 76% to 99%);
• occluded (grade 4 or 100%).

Fifty percent or greater stenosis was considered hemodynamically significant. Impression of overall image quality and presence, type, and severity of artifacts were recorded and graded for each patient.

Results
Patients with severe renal artery stenosis confirmed on digital subtraction angiography were significantly older than those without signs of renal artery stenosis. No MRA abnormality was found in 14 patients.

The remaining 15 patients had undergone subsequent digital subtraction angiography with angioplasty and/or stent placement.

All main and accessory renal arteries identified on MRA were confirmed at digital subtraction angiography. MRA did not detect any additional renal arteries that were not also found on digital subtraction angiography.

All stenoses were in the proximal third of the artery, and there were no stenoses found in the more distal aspects. These findings were equivalent with both MR and digital subtraction angiography.

Conclusions
Contrast-enhanced 3.0-T MRA, as compared with digital subtraction angiography, demonstrated a sensitivity of 94% and specificity of 96% with regard to detection of renal artery stenoses >75%. There were no artifacts degrading images in 21 of 29 patients.

Contrast-enhanced 3.0-T MR angiography is reliable in excluding renal artery stenosis.

Reviewer’s Comments
The results of this study are useful in that they demonstrate similar findings between contrast-enhanced 3.0-T MRA and digital subtraction angiography in the grading of renal artery stenosis.

This is likely related to the higher signal-to-noise ratio as well as improved spatial resolution of 3.0-T MR allowing for better depiction of renal arteries.

Therefore, contrast-enhanced 3.0-T MRA can be an excellent screening modality in patients suspected of having renovascular hypertension. A limitation noted in this study was the small number of patients.

Author: John C. Sabatino, MD, MSD

Reference:
Kramer U, Wiskirchen J, et al. Isotropic High-Spatial-Resolution Contrast-Enhanced 3.0-T MR Angiography in Patients Suspected of Having Renal Artery Stenosis. Radiology; 2008; 247 (April): 228-240