Fast Visualization of Needle Motion in Volume Rendered Image for Spine Biopsy Simulator Keun Ho Kim, Jong Beom Ra, and HyunWook Park Department of Electrical Engineering Korea Advanced Institute of Science and Technology Taejon, Korea ABSTRACT Spine biopsy is a useful tool to detect and verify spine tumor. We have developed a spine-biopsy simulation system, which provides realistic visual and force feedback information to a user. In this paper, we present an algorithm to combine a volume-rendered image and a surface-rendered needle image. The volume rendering requires a larger amount of computations and memory space. In general, the motion of a needle is fast so that image update should be performed frequently, whereas the viewing direction is not changed so fast in visualization, so that it is not necessary to update the volume rendered organ image frequently. The realization ofthe medical instruments can be performed by surface rendering rather than volume rendering to visualize the fast motion of the medical instruments. Surface rendering is an efficient method to render a simple structure with less computation and memory requirements. Fast combination of volume-rendered and surface-rendered images is performed with high quality realization. Keyword: Spine biopsy simulator, surface rendering, volume rendering, surgery simulator, composition 1. INTRODUCTION Since there are many critical organs near spine, the spine biopsy operation includes complicated and detail procedures. Therefore, the skilled training of operation is required before a medical doctor operates a patient directly. In the current spine biopsy operation, the medical doctor reads 2D CT images, and then he defines locations where the disease area is expected and the path which a needle enters the spine through. We have developed a spine biopsy simulation (SBS) system', which provides realistic visual and force feedback information to a user. The SBS system helps medical college students understand the structure oforgans near spine and train the operation of spine biopsy virtually without a real patient. This system includes several procedures mainly such as a visual feedback using 3D rendering, a segmentation method, graphic user interface (GUI), and a haptic feedback that gives the sense oftouch to a user2. 1.1. VIRTUAL REALITY AND SURGERY SIMULATOR With the development of medical technologies that reduce operation time and morbidity, surgical simulation3 appears to be an essential element of tomorrow's surgery. Indeed, most surgeons and students have to practice on an endotrainer, living animals, or cadavers. The lack ofrealism in the first solution and the ethical problems linked to the other solutions show a real need for simulated surgery. Several researchers have developed new ideas for a real-time surgery simulation system4 incorporating the following characteristics: a volumetric deformable model, a force feedback device, and real-time deformations based on a quasi non- linear biomedical behavior. Visual-realism and real-time interactions are essential in surgery simulation. Real-time interaction requires that any action of the operator generates an instantaneous response from the simulated organ in spite of the complexity of its geometry. Moreover, since all the organs in the human body are not rigid, their shape may be deformed during an operation. Consequently, the realism of the deformations is another key point in surgery simulation. This realism can be enhanced by the introduction of devices that allow a better immersion in the virtual world. In surgery simulation, the integration of a force feedback system to generate such sensation is of prime importance, almost as important as a visual feedback. When coupled with precise computations of the forces, it may be possible for the surgeon to feel haptic sensations close to reality. In Medical Imaging 2000: Image Display and Visualization, Seong K. Mun, 218 Editor, Proceedings of SPIE Vol. 3976 (2000) • 1605-7422/00/$1 5.00