Abstract: Radio -frequency ablation (RFA) is a minimally invasive image-guided method for local destruction of tumors. Successful ablation, or burning, of tumors, is impeded by blood flow in the vicinity of the tumor that tends to cool the tissue. We have developed methods for visualizing the tumors and their spatial relation to blood vessels for the purpose of treatment planning. We apply these methods to hepatic tumors. The visualization method employs contrast-enhanced (Gd-DTPA) magnetic resonance angiography (MRA) and magnetic resonance venography (MRV). The arteries and veins are delineated using the ordered region growing (ORG) skeletonization algorithm. Tumors are contoured manually. A shaded surface display is generated that includes the arteries, veins, and tumors. This three-dimensional map will be used to optimize treatment planning and to better limit the effects of perfusion on tumor ablation. A better understanding of the relationship of vessel location, size and flow to thermal lesion could facilitate improved outcomes.