Duplex Scanning in the Evaluation of Renal Arterial Occlusive Disease

Scanning Technique

The general principles of renal duplex scanning are identical to those for other arterial sites. After a renal artery is visualized using B-mode and color flow imaging, the pulsed Doppler sample volume is placed within the vessel. Spectral waveform analysis is then used to characterize the blood-flow pattern and classify the severity of disease. A localized flow disturbance with a high-velocity jet indicates the presence of a high-grade stenosis.

The challenge in renal artery scanning is to locate the vessels and obtain satisfactory pulsed Doppler information. Renal arteries are especially difficult to examine because of their small size, deep location, and variable anatomy. The effects of respiratory motion and overlying bowel gas can also limit the success of renal duplex scanning.

Whenever possible, patients should be examined after an overnight fast to minimize problems with abdominal gas. Low-frequency phased array or curved linear ultrasound transducers (2.25–3.0 MHz) are required for adequate depth penetration. Color-flow imaging is extremely helpful when performing abdominal vascular evaluations to help define anatomic relationships and identify blood vessels.

The abdominal aorta is evaluated initially to determine if there is aneurysmal or occlusive disease, and the aortic peak systolic velocity (PSV) is measured at the level of the superior mesenteric artery ( Figure 1 ). The origins of the main renal arteries are most commonly identified from a midline approach, with the aorta in transverse view, located just distal to the superior mesenteric artery, and near the level of the left renal vein as it crosses anterior to the aorta. An attempt should also be made to locate and evaluate accessory renal arteries.

Velocity spectral waveforms are recorded along the course of both main renal arteries and any accessory renal arteries, with particular emphasis on focal areas of increased velocity. The angle between the Doppler ultrasound beam and arterial wall should be 60 degrees or less for all velocity measurements. The distal renal arteries, as well as the hilar and parenchymal flow patterns, can be evaluated from a flank approach if they are not adequately imaged transabdominally. Measurements of kidney length have diagnostic value and should be included in the routine renal duplex evaluation.