Virtual environments for medical training: Graphical and haptic simulationof laparoscopic common bile duct exploration

We have developed a computer-based training system to simulate laparoscopic procedures in virtual environments (VEs) for medical training. The major h ardware components of our system include a computer monitor to display visu al interactions between three-dimensional (3-D) virtual models of organs an d instruments together with a pair of force feedback devices interfaced wit h laparoscopic instruments to simulate haptic interactions. In order to dem onstrate the practical utility of the training system, we have chosen to si mulate a surgical procedure that involves inserting a catheter into the cys tic duct using a pair of laparoscopic forceps. This procedure is performed during laparoscopic cholecystectomy (gallbladder removal) to search for gal lstones in the common bile duct. Using the proposed system, the user can be trained to grasp and insert a flexible and freely moving catheter into the deformable cystic duct in virtual environments. As the catheter and the du ct are manipulated via simulated laparoscopic. forceps, the associated defo rmations are displayed on the computer screen and the reaction forces are f ed back to the user through the force feedback devices. A hybrid modeling a pproach was developed to simulate the real-time visual and haptic interacti ons that take place between the forceps and the catheter, as well as the du ct; and between the catheter and the duct. This approach combines a finite element model and a particle model to simulate the flexible dynamics of the duct and the catheter, respectively. To simulate the deformable dynamics o f the duct in real-time using finite element procedures, a modal analysis a pproach was implemented such that only the most significant vibration modes of the duct were selected to compute the deformations and the interaction forces. The catheter was modeled using a set of virtual particles that were uniformly distributed along the centerline of catheter and connected to ea ch other via linear and torsional springs and damping elements. In order to convey to the user a sense of touching and manipulating deformable objects through force feedback devices, two haptic. interaction techniques that we have developed before were employed. The interactions between the particle s of the catheter and the duct were simulated using a point-based haptic in teraction technique. The interactions between the forceps and the duct as w ell as the catheter were simulated using the ray-based haptic. interaction technique where the laparoscopic. forceps were modeled as connected line se gments.