Surgical Simulators

Combining the sense of touch with 3-D computer models of organs, researchers at Rensselaer Polytechnic Institute are developing a new approach to training surgeons, much as pilots learn to fly on flight simulators. With collaborators at Harvard Medical School, Albany Medical Center, and the Massachusetts Institute of Technology, the team is developing a virtual simulator that will allow surgeons to touch, feel, and manipulate computer-generated organs with actual tool handles used in minimally invasive surgery (MIS).

“The most important single factor that determines the success of a surgical procedure is the skill of the surgeon,” said Suvranu De, assistant professor of mechanical, aerospace, and nuclear engineering and director of the Advanced Computational Research Lab at Rensselaer. It is therefore not surprising, he notes, that more people die each year from medical errors in hospitals than from motor vehicle accidents, breast cancer, or AIDS, according to a 2000 report by the Institute of Medicine.

De and his colleagues at Rensselaer are seeking to improve surgical training by developing a new type of virtual simulator. Based on the science of haptics — the study of sensing through touch — the new simulator will provide an immersive environment for surgeons to touch, feel, and manipulate computer-generated 3-D tissues and organs with tool handles used in actual surgery. Such a simulator could standardize the assessment of surgical skills and avert the need for cadavers and animals currently used in training, according to De.

“The sense of touch plays a fundamental role in the performance of a surgeon,” De said. “This is not a video game. People’s lives are at stake, so when training surgeons, you better be doing it well.”

Surgical simulators — even more than flight simulators — are based on intense computation. To program the realism of touch feedback from a surgical probe navigating through soft tissue, the researchers must develop efficient computer models that perform 30 times faster than real-time graphics, solving complex sets of partial differential equations about a thousand times a second, De said.

The major challenge to current technologies is the simulation of soft biological tissues, according to De. Such tissues are heterogeneous and viscoelastic, meaning they exhibit characteristics of both solids and liquids — similar to chewing gum or silly putty. And surgical procedures such as cutting and cauterizing are almost impossible to simulate with traditional techniques.

To overcome these barriers, De’s group has developed a new computational tool called the Point-Associated Finite Field (PAFF) approach, which models human tissue as a collection of particles with distinct, overlapping zones of influence that produce coordinated, elastic movements. A single point in space models each spot, while its relationship to nearby points is determined by the equations of physics. The localized points migrate along with the tip of the virtual instrument, much like a roving swarm of bees.