Medical Image Analysis (1998) volume 2, number 2, pp 121–132 c  Oxford University Press Volumetric object modeling for surgical simulation Sarah Gibson 1∗ , Christina Fyock 1 , Eric Grimson 2 , Takeo Kanade 3 , Ron Kikinis 4 , Hugh Lauer 1 , Neil McKenzie 1 , Andrew Mor 1,3 , Shin Nakajima 4 , Hide Ohkami 1 , Randy Osborne 1 , Joseph Samosky 2, 4 and Akira Sawada 1, 5 1 MERL, 201 Broadway, Cambridge, MA 02139, USA 2 Massachusetts Institute of Technology, Cambridge, MA, USA 3 Carnegie Mellon University, Pittsburgh, PA, USA 4 Brigham and Women’s Hospital, Boston, MA, USA 5 Mitsubishi Electric Corporation, Hyogo, Japan Abstract Surgical simulation has many applications in medical education, surgical training, surgical plan- ning and intra-operative assistance. However, extending current surface-based computer graphics methods to model phenomena such as the deformation, cutting, tearing or repairing of soft tissues poses significant challenges for real-time interactions. This paper discusses the use of volumetric methods for modeling complex anatomy and tissue interactions. New techniques are introduced that use volumetric methods for modeling soft-tissue deformation and tissue cutting at interactive rates. An initial prototype for simulating arthroscopic knee surgery is described which uses volumetric models of the knee derived from 3-D magnetic resonance imaging, visual feedback via real-time volume and polygon rendering, and haptic feedback provided by a force-feedback device. Keywords: surgical simulation, volume graphics, volumetric modeling Received March 3, 1997; revised July 7, 1997; accepted September 11, 1997 1. INTRODUCTION Computer-based surgical simulation has many applications in medical education, surgical training, surgical planning and intra-operative assistance. In education and training, surgical simulation can reduce costs associated with cadaver speci- mens, provide experience with a greater variety of pathologies and complications, and provide the ability to repeat or replay training procedures. In surgical planning, simulators can enable rehearsal of difficult procedures or planning on patient- specific anatomy and can enhance communication among medical professionals or between doctors and their patients. Intra-operatively, computer modeling can aid in navigation by augmenting the limited surgical field with a more global view of a patient’s anatomy. For example, computer modeling could provide guidance by preventing the surgical instrument from entering sensitive regions. ∗ Corresponding author (e-mail: gibson@merl.com) In order to provide useful feedback to the user, surgical simulators must provide adequate realism. Tissue models should respond in a realistic way when they are manipulated. Rendered images of the surgical field must be realistic enough to be compelling. Haptic or force feedback must mimic forces experienced in real-life because the sense of touch provides important cues in surgery. These requirements impose sig- nificant demands on the surgical simulator. These challenges include a need for physically realistic modeling (such as soft- tissue deformation and tissue cutting or tearing) and tradeoffs among physical and visual realism, the need for real-time interaction and cost. In computer graphics, objects are commonly represented by surface-based polygonal models. Because graphics workstations have special-purpose hardware for fast polygon rendering and because algorithms and systems have been developed for modeling physical interactions between (rigid) polygonal objects, currently there are advantages to using polygonal models in a surgical simulator. However, because