Safe superconducting current discharge for the magnetic stereotaxis system

The Magnetic Stereotaxis System is a unique neurosurgical device designed t o provide surgical treatment of regions of the brain normally inaccessible with contemporary techniques. By magnetically propagating a small (approxim ately 5 mm length, approximately 3 mm diameter) magnetic implant and attach ed catheter through the brain under near real-time fluoroscopic guidance wh ile referencing preoperative magnetic resonance imaging scans, both precisi on surgery and drug therapy can be applied to specific sites in the brain w hile circumventing the blood-brain barrier. Given the high current requirem ents for the proper operation of the system, a hazard exists in which a coi l may fail by either a coil quench or a magnet system shutdown, A silicon c ontrolled rectifier switch and varistor combine to circumvent this threat b y controlling the current discharge, thereby preventing damage to the cryog enic system while simultaneously protecting the patient, Analysis reveals t hat of the failures that may occur in the volume occupied by the brain, a f ield direction variation of up to 15 degrees at a magnitude of 0.10-0.15 T results for 70% of the cases, 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.