Characteristics of an improved coil structure for the magnetic stereotaxis system

The Magnetic Stereotaxis System (MSS) is a unique medical device designed to deliver drugs and other therapies directly into deep brain tissues. This approach uses superconducting coils to manipulate a small permanent magnet pellet attached to a catheter through the brain tissues. The movement of the small pellet is controlled by a remote computer and displayed on a fluoroscopic imaging system. The magnets of the previous generations were composed of three pairs of orthogonal superconducting solenoid coils. The control strategies are complex because of the magnetic field distribution of solenoids. The high inductance values of solenoid coils can severely slow down the ratio of current change and therefore do harm to the control precision of a magnet pellet. This paper presents a novel type of spherical coils that can generate linear gradient fields over a large spherical volume. This type of modified spherical coils with a constant current distribution model is easy to fabricate in engineering and manufacture. A prototype of this spherical magnet has already been constructed with copper conductors at the Applied Superconductivity Laboratory, CAS. We have also completed the design of superconducting spherical coils with NbTi conductors. Simulation and test results of this magnet are also presented.