Creating Biomedical Technologies to Improve Health


Science Highlight: November 30, 2007

Virtual Reality – Advances in Surgery Simulation

A new surgeon picks up the scalpel to begin his first emergency electrosurgery. He feels the resistance of the tissue, but it’s slippery – there is more blood than he expected. When he starts to cauterize the damaged artery, smoke adds to the challenge.

An established physician wants to offer gastric surgery to her patients struggling with obesity, but she has never seen it performed. How can she learn the procedure without putting her patients at risk?

These are just two instances in which surgical simulation could be used to help train doctors on new, rare, or infrequently performed procedures. Using surgical simulation, doctors can hone fine motor skills, practice procedures, and train other professionals without risk of error in the operating room. Current surgical simulation programs are valuable but have several limitations. The newly developed Point-Associated Finite Field (PAFF) approach integrates the strengths of current systems while avoiding some of the weaknesses, providing users a smooth visual display and more realistic touch response.

“We want it to be as realistic as possible in terms of what we see – for example, graphics – and what we feel, in terms of the touch response,” said Suvranu De, Associate Professor in the Department of Mechanical, Aerospace, and Nuclear Engineering at Rensselaer Polytechnic Institute.


From Aviation to the Operating Room

Drawing on his background in mechanical engineering, De began with methods commonly used to design and analyze aircraft in the aviation industry and simulate crashes in the automotive industry. “I quickly realized that you really can’t do that,” he explains. “There are many things in surgical simulations – for example, you’re cutting and tearing tissue; you’re burning tissue – those things don’t happen in the car industry or the aircraft industry. Besides, those existing methods are slow and non-interactive. So you have to have a fundamentally different method [for creating a surgical simulation].”

Surgical simulators provide visual and haptic (touch) responses to what the surgeon does with virtual “instruments” to mimic the use of real scalpels and other surgical instruments. When surgeons use the simulated scalpel to cut through a piece of tissue, they ideally feel the pressure response change according to the kind of tissue, the force of their strokes, and other environmental factors (bleeding, etc.).

In order to process the vast quantities of data required to produce that experience in real time, simulators are based on complex computational systems. However, the two most widely used systems (mass-spring systems and finite element analysis systems) do not always efficiently respond to the changing environments of delicate surgical procedures. Mass-spring systems offer speed, but they are so complex that their choices can be arbitrary and system stability might be compromised. Finite element analysis systems represent an object (e.g., an organ) by using multiple linked, simplified representations of different regions of the object on a grid, or mesh. In order to improve the image and have smooth touch-response, some systems refine the mesh with more elements. These “fine meshes” resolve some of the problems of mass-spring systems, but they also slow down response time, limit the number of contact points between virtual tools and tissues, and demand significant memory – all of which sacrifice flexibility in response to changing environments.

PAFF makes use of some strengths of these techniques, but it encompasses a new, meshless, and thus more flexible, system. PAFF is able to efficiently model large deformations of tissue, delicate surgical cutting, and other states of matter without compromising speed, thus creating a more realistic environment. Because frequent remeshing is unnecessary, real-time performance is protected and memory and computational resources are conserved.

This approach allows surgeons to experience different responses from different tissues, and thus hone their skills in dealing with soft, hard, and deformed organs. Cutting, bleeding, burning, and the smoke from cauterization can also be simulated within the same operation, without sacrificing the real-time haptic experience. For example, surgeons can now practice techniques, such as electrosurgery, that result in considerable smoke, which is difficult to represent in older systems.


Next Steps

Some of the country’s top medical students, residents, and surgeons will benefit from this new technology immediately upon its release. De and his colleagues have partnered with Beth Israel Deaconess Medical Center in Boston with the goal of developing a surgical simulator for its Center for Minimally Invasive Surgery. Daniel Jones, Associate Professor of Surgery at Harvard Medical School and Center Director, plans to implement PAFF in the Center’s Technical Skills and Simulation Lab as soon as it is complete.

De’s advances will help improve patient safety as well as doctors’ skills, says Jones. “If we really could integrate that into our training systems, operations would be much safer, because the mistakes would be made in a virtual world.”

De has also partnered with the Human Performance Institute at the University of Texas at Arlington for evaluation studies and Medical Education Technologies, Inc., to disseminate the software to the marketplace.


Expanded Possibilities

While surgical simulation has obvious utility as a training tool for residents and other medical professionals, established surgeons can also employ this method to practice rare procedures, learn new techniques, and train other surgeons. Without the risk of training exclusively in the operating room, new surgeons can refine their skills and receive standardized feedback according to defined evaluation parameters.

PAFF is currently directed toward use in bariatrics, a branch of medicine that deals with obesity and involves new procedures many doctors have not performed. For example, the high demand for new operations such as the laparoscopic adjustable gastric band has put pressure on surgeons, many of whom have not performed or even observed the procedure. “The question from the patient safety side is, ‘How are these guys actually going to be trained?’ In a virtual world, we’re able to go through all of the key steps to make that operation the best operation it can be,” says Jones. “That’s the beauty of a simulator.”

Because of its flexibility, however, De believes PAFF can be used in orthopedic, vascular, obstetric, gynecological, and neurological surgery. It “translates very well to all kinds of surgery,” according to De. “It is really how you train fine motor skills [in] any field – any kind of skill training using computers.”

This research is funded by the National Institute of Biomedical Imaging and Bioengineering.


De S, Lim Y, Manivannan M, Srinivasan MA. Physically realistic virtual surgery using the point-associated finite field (PAFF) approach. Presence: Teleoper. Virtual Environ. June 2006;15(3):294-308.

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