Figure 2. An example of the time–attenuation curve in portal perfusion measurement. Time–attenuation curve of relative enhancement (HU) of the liver, spleen (a), and subtracted liver (a pure portal venous curve separate from its arterial component) (b). Gs, the peak splenic gradient; Gl, the peak gradient of original hepatic time–attenuation curve; Gp, the peak gradient of subtracted hepatic time–attenuation curve in the portal venous phase.