Figure 5. Perfusion estimation from enhancement gradient in a single parenchyma voxel. In each figure the dashed line shows the splenic arterial peak, separating arterial from portal phase; the red line shows the smoothed uptake curve from which gradients are taken; the black line shows measured gradient. (a) Peak uptake gradient during the arterial phase. (b) The estimated portal contribution (after subtraction of a scaled spleen curve), and peak gradient measured from this during the portal phase. The measured gradient during the portal phase in this parenchyma voxel exceeds that in the arterial phase.