Magnetic tools enhance surgical techniques.

The magic of magnetism lies in its ability to act at a distance. Now, a team of physicists and neurosurgeons has built a system that uses magnetic fields to assist in brain surgery.

The magnetic stereotaxis system, developed by Stereotaxis and the Washington University School of Medicine's Barnes-Jewish Hospital, both in St. Louis, uses magnetic force to guide a pellet through brain tissue to inoperable tumors or other hard-to-reach locations. Surgeons believe they will be able to use the pellets to deliver treatments.

"The magnetic pellet acts like a tugboat," says Matthew A. Howard III, a neurosurgeon at the University of Iowa Hospitals and Clinics in Iowa City. "It can pull a catheter into position, deliver radioactive sources, implant electrodes, or move a drug pump into place. It does the least amount of damage to brain tissue."

The magnetic system, which has proven successful in pigs, should eliminate the need for cutting open a large section of the skull. Instead, a physician would make a tiny incision, lay a magnetic pellet on the brain's surface, and place the patient's head in a special helmet, says George T. Gillies, a physicist at the University of Virginia in Charlottesville. In the helmet, an array of six computer-controlled superconducting magnets applies forces to move the pellet along a predetermined course designed t o minimize damage.

In animal tests, the new system has proved accurate to within a fraction of a millimeter, says Rogers C. Ritter, also a physicist at the University of Virginia. The system's designers hope to begin clinical trials next year.