In the operation, a catheter was moved by superconducting magnets through a patient's brain in order to retrieve a biopsy sample of a tumour. The path was plotted on a brain scan by a surgeon using a computer mouse.

"This is a fundamentally new approach to guiding surgical instruments during brain surgery," explained the surgeon Dr Ralph Dacey of the Department of Neurological Surgery at Washington University School of Medicine in St. Louis.

Images of the brain are used to plot the course of the catheter

"Not only does this system allow us to follow a curved path through the brain, but for the first time a computer is able to steer a catheter using externally applied magnetic fields acting on the catheter tip, giving us greater navigational control."

Currently surgeons visualise the location of a brain tumour through imaging technology, but must manually guide surgical instruments on a straight-line path to the target location, potentially damaging vital brain tissue.

Magnetic seed

Michael Lawson of Stereotaxis, the company that developed the system, explained how it works. A thin, flexible guidewire is tipped with a magnetic seed the size of a grain of rice and fits into a catheter.

The guidewire and catheter are inserted into a small hole in the skull from where the surgeon maps out the path to be travelled on a computer

The computer adjusts the magnetic field of the superconducting magnets that surround the patient's head, pulling the catheter along the chosen path through the brain.

The computer recalculates the position and the trajectory of the catheter after every millimetre moved, but it takes less than five minutes to reach its target deep in the skull.

The catheter can be guided along a curved path

Once at the potential tumour, the guidewire is withdrawn, leaving the catheter in place. A highly flexible biopsy tool is inserted, the biopsy is taken and the catheter is removed.

The pioneering operation was successfully conducted last Thursday on a 31 year-old volunteer who had been diagnosed with a tumour in the frontal lobe of his brain.

Clinical trials

In all, five patients will participate in the first clinical trial at the Barnes-Jewish Hospital, which has been permitted under a U.S. Food and Drug Administration Investigational Device Exemption.

A second, larger clinical trial is planned and Stereotaxis believes the system could be commercially available in two to three years. The system is the first to integrate the magnetic control of surgical tools with X-ray and MRI scans of the brain.