Operating with Magnets

By Jim Wilson
Popular Mechanics, August 8, 2003

If you want to know why brain surgeons earn the big bucks, make a big bowl of Jell-O and canned fruit. After it sets, try to scoop out the center of one of the grapes, without removing its skin. Neurosurgeons actually do practice with a Jell-O-based brain substitute. Stereotaxis, a St. Louis-based company, also mixes big batches of this imitation gray matter, so neurosurgeons can practice using its computer-controlled machine to operate on currently inaccessible parts of the brain.

The machine is called the Magnetic Surgery System (MSS) and it works exactly as its name suggests. A few days before Christmas, surgeons at Barnes-Jewish Hospital in St. Louis used it for the first time on a human patient. As though picking up nails with a magnet, the MSS guided an ant-size instrument along a circuitous route into the frontal lobe of a 31-year-old man, enabling the surgeons to remove a piece of tissue from an otherwise inoperable part of the brain.

"This is a fundamentally new way of manipulating surgical tools within the brain that promises to be minimally invasive," says Ralph Dacey. The head of neurological surgery at Washington University School of Medicine in St. Louis, and lead surgeon for the operation just described, Dacey has FDA permission to test the MSS by performing biopsies on five patients with tumors in the upper front part of the brain. "It should be a safer way of doing brain surgery because it allows us to use a curved pathway to reach a target. We can go around sensitive structures, such as those that control speech or vision, instead of going through them."

Into The Brain

Dacey began the history-making operation by drilling a small hole, about the diameter of a pinkie finger, through the top of his patient''s skull. As soon as the last bone fragments were swept clear, he temporarily closed the opening with a plastic bolt. Six small pieces of metal that would later serve as markers were then attached to the outside of the skull.

Moving to the computer console that controls the MSS, Dacey then studied a series of magnetic resonance images of the patient''s brain, similar to the one shown here. With him as he reviewed these virtual slices of the brain were two of the machine''s inventors, Matthew A. Howard III, associate professor of neurosurgery at the University of Iowa, and M. Sean Grady, professor of neurosurgery at the University of Washington.

In 1984, Howard thought of using a magnetic field to guide surgical instruments into the brain. He and Grady, then a neurosurgery resident, approached University of Virginia professor of physics Rogers Ritter for help in working out the details. For the next few years, the three men and George T. Gillies, a research professor of mechanical engineering and biomedical engineering at the University of Virginia, conducted a series of feasibility studies to determine if the radical idea might actually work.

By 1990, they had enough data to convince Sanderling, a Menlo Park, Calif., venture capital company, to bankroll their new company, Stereotaxis. Four years ago, the company moved to St. Louis to be near the Washington University School of Medicine and Barnes-Jewish Hospital. The outcome of those years of research, millions of dollars of investment and hours spent slaving over Jell-O now hinged on the outcome of the revolutionary operation that had just begun.

With a safe route to the tumor mapped, the patient''s head was placed in the MSS, where it was positioned between three sets of superconducting magnets. The plastic bolt that temporarily sealed the hole in the skull was removed. A tiny magnet attached to a guidewire, surrounded by a spaghetti-thin plastic catheter, was gently pressed against the patient''s brain.

Tunnel Opening

With instruments in position, Dacey moved from the operating table to the nearby MSS console, and slowly guided the small magnet toward the tumor. The "pull" was provided by the attraction of a series of rapidly changing magnetic fields that the superconducting magnets created within the patient''s brain. The head of the guidewire followed the advancing magnet field, slowly cutting a curved route to the tumor, in precise 1mm steps.

To assure the surgeons it was on track, MSS snapped a fluoroscope image of the patient''s head about every 2 seconds. On the screen the six metal markers inserted earlier acted as reference points, micromilestones on the magnet''s trip into the brain.

After about 5 minutes, the image on the MSS display–which merged the fluoroscope''s X-ray with a magnetic resonance image that showed the detail of soft tissue–revealed that the magnet had reached the edge of the tumor. Dacey returned to the operating table, where he ever so gently pulled the magnet-led guidewire out of the patient''s brain. Through the catheter Dacey passed an ant-size, tweezers-like tool, pushed by a flexible rod. A few minutes later the first of several tissue samples was on its way to the pathology lab for a microscopic examination that would determine the course of future treatments.

Until this operation there had been no way to automatically navigate tools through the brain. Generally, neurosurgeons obtain biopsies by pushing a needle toward a tumor, passing through and often destroying whatever structures are in the way.

Convincing The FDA

Biopsies are only the beginning. "We expect the system to have a wide range of applications because the Magnetic Surgery System puts three components–visualization, localization and navigation–together for the first time," says Bevil Hogg, CEO of Stereotaxis. "Future possibilities may include implanting electrodes into the brains of patients with movement disorders, repairing aneurysms and other blood vessel abnormalities, delivering therapeutic drugs or chemotherapy agents to parts of the brain, cardiac electrophysiology and removal of arterial plaque."

Before any of this can happen, the FDA needs to be convinced. Four operations similar to the historic surgery must be completed before Stereotaxis can ask the FDA for permission to proceed to the second phase of human trials, which will involve about 30 patients at a medical school other than Washington University. If these Phase II trials are successful, magnets could become as basic a surgical tool as the scalpel.