Duplex Imaging of the Renal Arteries with Contrast Enhancement

Duplex ultrasound evaluation of the renal arteries is a technically challenging procedure. Its accuracy is significantly influenced by operator expertise and patient factors, such as overlying bowel gas and obesity. Intravenous microbubble contrast agents enhance vascular reflective acoustic signals and may improve ultrasound diagnostic accuracy. The clinical usefulness of such a contrast agent in the renal vasculature was examined prospectively. A total of 22 patients (16 males and 6 females) with mean age of 63 ±3 years with suspected abdominal vascular disease were studied prospectively. A complete color flow duplex imaging study of the renal vasculature was performed. This was then followed by an identical examination during which an ultrasound contrast agent (Definity™, DuPont Pharmaceutical) was infused intravenously at a rate of 2 to 4 mL/min. In addition to imaging of the vessels, the peak systolic velocity and Doppler waveforms of the aorta and renal arteries were examined. These results were independently compared to results with contrast angiography. A mean of 67 mL of contrast was used per patient. Of the total of 43 renal arteries examined, the accuracy for the detection of occlusions was 75% (3 of 4) for both standard and contrast-enhanced duplex ultrasound. The accuracy for the detection of hemodynamically significant stenosis was 50% (6 of 12) for standard and 75% (9 of 12) for contrast-enhanced duplex ultrasound. Visualization of normal or minimally diseased arteries was 94% (30 of 32) for standard and 97% (31 of 32) for contrast-enhanced ultrasound. Although overall accuracy was not enhanced by the infusion of ultrasound contrast, 5 of 7 arteries not visualized by color flow duplex were detected following the infusion of contrast agent, resulting in an additional 10% (5 of 48) of vessels visualized. Peak systolic velocities were increased by an average of 10% in normal or minimally diseased vessels and 12% in stenotic vessels following contrast administration but these differences were not statistically significant. Contrast-enhanced duplex imaging of the renal arteries is safe but not routinely required when performed by an experienced sonographer. However, it may increase visualization and accuracy in patients with stenoses or when the vessels are not initially visualized. Although increased velocities are seen when contrast agent is used, this does not appear to necessitate different Doppler criteria at this time.