Normal spectral waveforms from different segments of the hepatic artery. (a) Spectrum from the hepatic artery at the porta hepatis in a 4-day-old girl demonstrates low-resistance and high-velocity diastolic flow. (b) Spectrum from the left branch of the hepatic artery in a 13-year-old boy shows lower resistance than that in a. The calculated RI also was lower.

The direction of blood flow in the hepatic artery is hepatopetal (toward the liver). Hepatic artery waveforms demonstrate low resistance and high diastolic flow velocities (Fig a). Normal hepatic arterial PSV in a fasting adult patient is approximately 30–40 cm/sec, and EDV is 10–15 cm/sec . The normal RI in a fasting patient varies from 0.55 to 0.81 (mean, 0.62–0.74). There is a consensus that the RI increases after a meal and also with age . The RI is higher at the porta hepatis (Fig a) and lower in vessel branches closer to the periphery of the liver (Fig b).

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