A support system for hepatectomy that allows segmentation of the liver inte
ractively and directly on 3D images was developed. Intuitive 3D images of t
he liver and its vessels and tumors were drawn with an improved volume-rend
ering method. Regions supplied with blood by each branch were interactively
identified. 3D segments were defined directly on the images using a mouse
and excisions were estimated from these interactive inputs.