Sonographers should follow a standard imaging protocol. A complete evaluation includes B-mode imaging, spectral Doppler analysis, and color Doppler imaging of all accessible portions of the renal arteries. Bilateral evaluations are essential for a complete evaluation; however, studies may be unilateral based on laboratory-specific protocols.

Throughout each examination, the sonographer or examiner should:

• Observe sonographic characteristics of normal and abnormal tissues, structures, and blood flow, allowing necessary adjustments to optimize exam quality
• Assess and monitor the patient’s physical and mental status, allowing modifications to the procedure plan according to the patient’s clinical status
• Analyze sonographic findings to ensure that sufficient data is provided to the physician to direct patient management and render a final diagnosis
• Accurately annotate B-mode, color and spectral Doppler images

Complete Renal Artery Duplex Exam

A complete renal artery duplex exam includes evaluation of the abdominal aorta, main renal arteries, renal veins, parenchymal arteries and the kidneys.

B-mode imaging should be performed in longitudinal and transverse planes. Optimize the gain to depict vessel walls, plaque and any other abnormalities. Color Doppler may be used to depict areas of abnormal flow or significant stenosis. Power Doppler is useful to confirm areas of possible vessel occlusion or low flow states.

B-Mode images should include the following:

• Maximum diameter of the abdominal aorta should be obtained in longitudinal and transverse planes
• Longitudinal length measurements of the kidneys
  • Obtain three length measurements per kidney to increase accuracy
  • Cysts, masses and hydronephrosis should be documented
• Renal Cortex thickness measurements should be obtained in the transverse plane if required by facility protocol
• Renal arteries (if adequately seen in B-Mode)
• Renal veins

Color Doppler images should include the following:

• Renal arteries
• Renal veins
• Segmental and parenchymal arteries within the kidney

Velocity measurements should be obtained from a longitudinal plane at an angle of 60° parallel to the direction of the blood flow/vessel walls. Maintain a Doppler angle between 45° and 60° whenever possible. Angles greater than 60° must be avoided. Doppler angles less than 45° may be necessary due to patient anatomy. To obtain peak velocity, utilize color Doppler to note areas of concern and “walk” the spectral Doppler cursor throughout these areas. Post-stenotic turbulence should be documented when present.

Spectral Doppler waveforms and velocity measurements must include the:

• Mid aorta at the level of the renal arteries
• Origin, proximal, mid and distal portions of the main renal arteries
  • Accessory renal arteries (when present)
  • Renal artery stents (when present)
• Segmental arteries at the upper, mid and lower poles
  • Used to obtain the resistive index (RI)
• Renal veins for patency (does not require velocity measurements)
• Inferior vena cava (does not require velocity measurements)

Indirect Testing of the Renal Arteries

Indirect testing of the renal arteries includes spectral Doppler analysis of the parenchymal arteries in order to infer main renal artery stenosis.

B-Mode images should include:

• Longitudinal length measurements of the kidneys
  • Should obtain multiple length measurements to increase accuracy
  • Cysts, masses and hydronephrosis should be documented
• Renal Cortex thickness measurements should be obtained in the transverse plane if required by facility protocol

Color Doppler images should include the following:

• Segmental and parenchymal arteries within the kidney

Spectral Doppler waveforms and velocity measurements should include:

• Segmental, interlobar or arcuate arteries in the upper, mid and lower poles
  • Obtain the pulsatility index (PI), resistive index (RI) and the acceleration time or acceleration index from the parenchymal vessels as per facility protocol
    • Typically, angle correction is not used to obtain renal parenchymal velocity measurements.

Renal artery stents

• Evaluate with B-mode imaging to visualize the stent.
• Evaluate with color Doppler to identify color flow changes that may indicate actual flow change, variation in the residual lumen, the presence of an obstruction/restenosis and incorrect stent location or migration of the stent.
• Angle corrected Doppler spectral waveforms obtained proximal to the stent, within the stent and distal to the stent (45 to 60 degrees and parallel with the vessel wall, 60 degrees is optimal)
• The diameter of the stented segment of the renal artery may be slightly larger than the native renal artery. This diameter change can result in increased peak systolic velocity as the blood moves from a larger diameter to the smaller diameter of the non-stented artery.
• The stent should be evaluated for correct placement within the renal artery. If there is a distinct flow disturbance within the aorta at the level of the renal artery, this may be an indication that the stent is protruding into the lumen of the aorta.