Safe superconducting current discharge for the magnetic stereotaxis system

The Magnetic Stereotaxis System is a unique neurosurgical device designed to provide surgical treatment of regions of the brain normally inaccessible with contemporary techniques. By magnetically propagating a small (approximately 5 mm length, approximately 3 mm diameter) magnetic implant and attached catheter through the brain under near real-time fluoroscopic guidance while referencing preoperative magnetic resonance imaging scans, both precision surgery and drug therapy can be applied to specific sites in the brain while circumventing the blood-brain barrier. Given the high current requirements for the proper operation of the system, a hazard exists in which a coil may fail by either a coil quench or a magnet system shutdown. A silicon controlled rectifier switch and varistor combine to circumvent this threat by controlling the current discharge, thereby preventing damage to the cryogenic system while simultaneously protecting the patient. Analysis reveals that of the failures that may occur in the volume occupied by the brain, a field direction variation of up to 150 at a magnitude of 0.10-0.15 T results for 70% of the casts, 0.15-0.20 T for 50%, 0.20-0.25 T for 25%, and 0.25-0.30 T for 5%. In no circumstance does the force magnitude increase.