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

OBJECTIVE. We investigated the usefulness of phase-contrast MR imaging to m easure renal artery velocity waveforms as an adjunct to renal MR angiograph y. We also examined whether an angiotensin-converting enzyme (ACE) inhibito r improves the diagnostic accuracy of waveform analysis. SUBJECTS AND METHODS. Thirty-five patients referred for MR angiography of r enal arteries underwent non-breath-hold oblique sagittal velocity-encoded p hase-contrast MR imaging through both renal hila (TR/TE, 24/5; flip angle, 30 degrees; signal averages, two; encoding velocity, 75 cm/sec) before and after IV administrastion of an ACE inhibitor (enalaprilat). We analyzed vel ocity waveforms using established Doppler sonographic criteria. A timing ex amination with a test bolus of gadolinium contrast material was performed t o ensure optimal arterial enhancement during breath-hold gadolinium-enhance d three-dimensional gradient-echo MR angiography. RESULTS. MR phase-contrast waveform pattern analysis was 50% (9/18) sensiti ve and 78% (40/51) specific for the detection of renal artery stenosis equa l to or greater than 60% as shown on MR angiography. Sensitivity (67%, 12/1 8) and specificity (84%, 42/50) increased slightly, but not significantly, after TV administration of an ACE inhibitor. Also, the accuracy of quantita tive criteria such as acceleration time and acceleration index did not impr ove 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 insuffic iently accurate to use in predicting renal artery stenosis.