Figure 2b. Normal Doppler US appearance. (a) Subcostal oblique color and spectral Doppler image of the right hepatic vein shows normal venous phasicity due to respiration. (b) Intercostal color and spectral Doppler image of the main portal vein shows a normal continuous waveform with mild velocity variations due to respiration. (c) Intercostal color and spectral Doppler image of a normal hepatic artery at the porta hepatis shows a rapid systolic upstroke with continuous low-velocity diastolic flow.