Angiotensin-converting enzyme inhibitor-enhanced phase-contrast MR imaging to measure renal artery velocity waveforms in patients with suspected renovascular hypertension

OBJECTIVE. We investigated the usefulness of phase-contrast MR imaging to measure renal artery velocity waveforms as an adjunct to renal MR angiography. We also examined whether an angiotensin-converting enzyme (ACE) inhibitor improves the diagnostic accuracy of waveform analysis. SUBJECTS AND METHODS. Thirty-five patients referred for MR angiography of renal arteries underwent non-breath-hold oblique sagittal velocity-encoded phase-contrast MR imaging through both renal hila (TR/TE, 24/5; flip angle, 30°; signal averages, two; encoding velocity, 75 cm/sec) before and after IV administration of an ACE inhibitor (enalaprilat). We analyzed velocity waveforms using established Doppler sonographic criteria. A timing examination with a test bolus of gadolinium contrast material was performed to ensure optimal arterial enhancement during breath-hold gadolinium-enhanced three-dimensional gradient-echo MR angiography. RESULTS. MR phase-contrast waveform pattern analysis was 50% (9/18) sensitive and 78% (40/51) specific for the detection of renal artery stenosis equal to or greater than 60% as shown on MR angiography. Sensitivity (67%, 12/18) and specificity (84%, 42/50) increased slightly, but not significantly, after IV administration of an ACE inhibitor. Also, the accuracy of quantitative criteria such as acceleration time and acceleration index did not improve after the administration of ACE inhibitor. CONCLUSION. Renal hilar velocity waveforms, measured using non-breath-hold MR phase-contrast techniques with or without an ACE inhibitor, are insufficiently accurate to use in predicting renal artery stenosis.