A MAGNET which can guide surgical instruments through the brain is being developed by Oxford Instruments.

Its Superconductivity subsidiary, based at Tubney Wood, near Abingdon, is building magnets for a system created by US company Stereotaxis Inc.

Surgeons believe it could be used to take sample cells from brain tumours to test for cancer and would be less invasive and more effective than conventional surgery. The technique, being tested in US hospitals, could also be used for other surgery.

A magnetic tip attached to a fine flexible guidewire is inserted through the groin, then guided to the brain by rapid adjustments to the magnetic fields of three superconducting magnets placed around the patient's head.

A real-time X-ray image, showing two planes of the head, provides the surgeon with direct, visual control of the tip. Position is determined to within 1mm. Once in position the magnetic tip is withdrawn, enabling a flexible biopsy tool to be inserted.

Oxford Instruments has worked with Stereotaxis to meet the demanding magnetic specification. The magnet consists of three 40cm diameter superconducting coils, mounted around the patient's head. The surgeions need extremely rapid alteration of the magnetic field, very high voltages from the power supply and high-grade superconducting wire.

The magnets are subjected to high stresses, so components must be designed to ensure the coils do not distort.

The Stereotaxis link-up is one of several new contracts which have caused the company to launch a recruitment drive for 40 engineers and 40 technicians.