Virtual blood and smoke give gore to student surgeons

SPILT blood and burning flesh can now be modelled accurately. But you won't find the software in a gory shoot-'em-up video game, at least not yet. Instead it will used to make virtual surgery look more lifelike.

Like airline pilots, surgeons practise their trade using simulators. For keyhole surgery routines they use a dummy torso with mock organs and a variety of grasping, cutting and cauterising tools. Transducers in the organs sense the forces exerted by the instruments and feed them to a PC, which screens a virtual representation of how real organs would respond.

But merely simulating how the organs respond to the tools and move against each other in real time takes up most of a top-end PC's number-crunching power, says Suvranu De, an engineer at Rensselaer Polytechnic Institute in Troy, New York. That means other important aspects of surgery have to go unmodelled, reducing the realism of the simulation.

"Intra-abdominal tissue has a very high density of blood vessels. When a cauterising device cuts it, copious amounts of smoke are generated and bleeding may occur. These effects are hard to incorporate in a simulation," says De. That's because such simulations would involve solving fluid dynamics equations every time the blood or smoke moves, something existing technology takes several hours to do.

To get around this problem, De's team has developed a technique that instead overlays pre-programmed visual effects onto the simulations.

First, they took sample video footage from real keyhole surgery showing how smoke can obscure the surgeon's view. These clips were of both the dense smoke coming from the tip of the cauterising tool and the wispy smoke further away.

They stored these sequences and wrote an algorithm that enables the PC's graphics processor to call them up whenever the cauterising tool is used. The software updates the overlaid images at a rate of 30 frames per second - fast enough to give an interactive feel to the simulation. The smoke density in each image depends upon the length of time the tool is used as well as distance from the cauterised site.

To simulate the degree of bleeding, another algorithm consults a database of the vascular density at the point of interest in the body. It then estimates the likely bleeding rate, depending on the depth of the surgeon's cut, and brings up animation sequences of the appropriate amount of pooling blood to overlay on the simulation.

The team hopes to refine the software further to improve its realism - and could even transfer it to video games. "This is a very clever way to do it," says Vincent Luboz at Imperial College London, who works on surgery simulators. But he adds that the technique is more suited to general training than to rehearsing an operation on a particular patient.