Normal spectral waveforms from renal arteries. (a) Spectrum from the midportion of the right renal artery in a 2-day-old girl demonstrates a prominent systolic peak, with antegrade flow throughout diastole. (b) Spectrum from an intraparenchymal renal artery in a preterm 26-day-old girl shows relatively high resistance (RI of 0.88), which is considered normal for preterm neonates.

Arterial flow in the main renal vessels and within the renal parenchyma demonstrates a prominent systolic peak, with antegrade diastolic flow present throughout the cardiac cycle (Fig ). The normal PSV in adults is 100–180 cm/sec, and the normal EDV is 25–50 cm/sec . The normal ratio of renal artery PSV to aortic PSV is less than 3.5 .

http://radiographics.rsna.org/content/28/3/691.full