At the Forschungzentrum Karlsruhe, researchers have developed a virtual reality based training system for the simulation of diverse minimally invasive surgical tasks. This endoscopic surgery trainer consists of a high performance graphics workstation as core unit, running on the multipurpose KISMET software, which stands for Kinematic Simulation, Monitoring and Off-line Programming Environment for Telerobotics. The KISMET package has been extended for medical applications with haptic feedback interfaces, in order to calculate in real time the interaction between deformable objects and surgical instruments. In this way, the trainee is able to accurately track both the manipulations of the virtual tissues and the physical force feedback resulting from the object manipulation.
Minimally invasive surgery and endoscopic procedures require a great amount of experience and skill from the surgeon. Sufficient practice on a simulation system enables him to improve the delicate hand-eye and instrument coordination, as well as to train the use of new instruments and surgical interventions. In Karlsruhe, the research team is working with a Silicon Graphics' Onyx workstation, including an RE2 graphics subsystem and two processors, to provide the trainee with a virtual operation area and a real time "synthetic" endoscopic view. He can also choose to wear shutter glasses with full stereo view to obtain a 3D impression of the geometrical shapes and physical properties of organs, tissues, and vessels.
Specifically in laparoscopic procedures, a "phantom box" is introduced into the simulation environment, which serves as a surgeon-computer interface. It constitutes in fact a rough imitation of the outward human abdomen and offers the trainee an artificial cavity, incorporating electromechanical instrument guidance and tracking systems for cameras. In addition, several foot switches generate typical surgical tasks, such as grasping, cutting, coagulating, and setting of clips. During the training sessions, it is possible to implement unexpected complications or anatomic specialities to test the surgeon's attention and flexible reaction. Afterwards, operating scenarios may be reproduced for repeated training or evaluation by expert system feedback.
For the trainee, it is very important to obtain a realistic sensation of the interaction of the soft tissue and its physical behaviour with the surgical instruments. This leads to a system of deformable objects which include the design of a homogeneous modelling concept, integrating both physical and geometrical modelling as well as model interaction and manipulation. For this purpose, the researchers have developed a mathematical model in which the model mass is discretized to zero-dimensional mass-knots, connected by binding elements, and resulting in a so-called nodal net model. Once this finite element system has been created, the geometrical models of the deformable objects have to be graphically represented.
This can be done in two ways, whether by generating free-form surfaces or Non Uniform Rational B-Spline Surfaces (NURBS) or by direct output of polygonal nets or extended polyhedrons. In order to connect the physical with the geometrical model, the positions of the mass knots are projected onto the matching NURBS or vertices of the polygonal net. The models then are ready for real time interaction, such as collision recognition, grasping, cutting, coagulating and clip application. For this kind of complex force feedback actions, three different types of haptic feedback interfaces are used, namely the Immersion Corporation's Laparoscopic Impulse Engine; the PHANToM from SensAble Technologies; and the HIT device, designed by Hauptabteilung Ingenieurtechnik.
The instruments have 5 degrees of freedom for motion and tracking, with 3 degrees of freedom equipped with motors, providing feedback. If a sudden interaction between the simulated instrument and a deformable object occurs, the forces acting on the tip of the instrument are calculated by the KISMET simulation system. After transformation into forces or torques, acting on each degree of freedom, these measures are used as input for a micro-controller-box, monitoring the motors. As a result the surgeon will experience contact forces. The Karlsruhe team is fully involved in ongoing efforts to enhance the level of realism within the virtual environment, such as the introduction of bleeding and of tools for the automatic generation of models with patient specific Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) data sets. At their Web site, you can learn more about the Endoscopic Surgery Trainer.