An international multicenter comparison of time-SLIP unenhanced MR angiography and contrast-enhanced CT angiography for assessing renal artery stenosis: the renal artery contrast-free trial.

OBJECTIVE: The unenhanced MR angiography (MRA) technique time-spatial labeling inversion pulse (time-SLIP) may provide a safe alternative for evaluating the renal arteries for stenosis. This international multicenter trial tested the hypothesis that time-SLIP unenhanced MRA is accurate and robust for assessing the renal arteries for stenosis in comparison with contrast-enhanced CT angiography (CTA). SUBJECTS AND METHODS: Four centers (United States, Europe, Asia) enrolled 75 patients (average age ± SD, 58 ± 13 years; 41 [55%] men and 34 [45%] women). Each patient underwent abdominal contrast-enhanced CTA and abdominal unenhanced MRA using time-SLIP with balanced steady-state free precession. All images were visually assessed for quality (arterial signal intensity) and for the absence or presence of renal artery stenosis (≤ 50% or > 50% stenosis, respectively). In addition, for arteries with any visible disease, the severity of the stenosis was quantified. Two blinded readers evaluated each study. No arteries were excluded from analysis. RESULTS: Unenhanced MRA image quality was excellent for 56 of 75 patients (75%) and good for 16 of 75 patients (21%). CTA was used as the reference standard and showed that 23 of 161 renal arteries (14.3%) had stenosis > 50%. Unenhanced MRA correctly classified 17 of the 23 renal arteries with > 50% stenosis and correctly classified 128 of the 138 renal arteries as not having disease (≤ 50% stenosis) to yield a sensitivity of 74%, specificity of 93%, and accuracy of 90% (χ(2) = 0.56; p = 0.45, no statistically significant difference). Of the 16 misclassified arteries, only three had a clinically relevant misclassification (CTA ≥ 70% stenosis and unenhanced MRA ≤ 50% stenosis or unenhanced MRA ≥ 70% stenosis and CTA ≤ 50% stenosis). On average, measured stenotic severity (n = 28 arteries) was similar for unenhanced MRA (64% ± 17%) and CTA (62% ± 16%) (p = 0.51). CONCLUSION: Compared with contrast-enhanced CTA, the unenhanced MRA technique time-SLIP shows promise for assessing the renal arteries for stenosis. The unenhanced MRA technique time-SLIP may provide a safe alternative for evaluating the renal arteries for stenosis.