Figure 7. Portal vein stenosis. Gray-scale US (top left), color Doppler (top right), and spectral Doppler (bottom) images of the long axis of the main portal vein show focal color aliasing (second arrow) at the vascular anastomosis. The waveforms show a greater than sixfold velocity in the poststenotic segment (first arrow) relative to the velocity in the prestenotic segment (third arrow), a finding consistent with a significant stenosis.