Criteria for > 60% Stenosis
Renal-Aortic Ratio (RAR) (renal PSV divided by aortic PSV) >3.5. Peak systolic velocity (PSV) >180 cm/s. Post-stenotic turbulence. Low flow velocity in distal renal artery.

Kohler TR, Zeirler RE, Martin RL et al. Nonivasive Diagnosis of Renal Artery Stenosis By Ultrasonic Duplex Scanning. J Vasc Surg 1986;4;450-6.

Taylor DC, Kettler MD, Moneta GL, et al. Duplex Ultrasound scanning in the diagnosis of renal artery stenosis: A prospective evaluation. J Vasc Surg 1988;7:363-9

Hansen KJ,Tribble RW, Reavis SW, et al., Renal duplex sonography: Evaluation of clinical utility. J Vasc Surg 1990;12:227-36