Advanced medical imaging techniques available today, such as CT, MRI, and PET, are capable of producing large quantities of near isotropically-sampled data. These datasets coupled with advanced techniques in Computer graphics can create new ways to explore cross-sectional medical images. We hypothesize that 3-D renderings of the imaging data may provide enhanced diagnostic interpretation and superior visualization for treatment planning purposes. We have investigated the application of Perspective Volume Rendering (PVR) as a method to facilitate interactive exploration of various tubular structures. In this paper we will explore the results from four noninvasive applications of PVR: 1) detection and studies of aneurysms in the circle of Willis, 2) studies of thoracic aorta aneurysms, 3) assessment of bronchial anastamoses and 4) detection of polyps in colonic lumen.