Study On Focality Of Magnetic Stimulation Based On Multiple Coils

Transcranial magnetic stimulation(TMS) has been applied widely by its prominent advantages of pain-free and non-invasive and stimulation depth and so on. TMS has been used in treatment of depression and Parkinson diseases with efficacious of treatment. At the same time, some better treatment effects of recovery from fatigue, bone healing, insomnia and motor function of cerebral palsy for children have been achieved. As is known, the key problem of TMS is stimulation focality, which is basically dependent on the coils design. The magnetic field distribution of different coils has been investigated with the numerical method by the employing MATLAB software which includes the following contents:The development of coil design of TMS have been briefly introduced. The basic principle, calculation method and results of circular and figure-of-eight coils were described in detail. The stimulation performance of either circular or figure-of-eight coils was improved by bending the coils along its center line, or by employing the multiple figure-of-eight coils.When the traditional circular and figure-of-eight coils have been changed with the coils bending at the different position apart from the center, the best bending angles and the best bending coils of the induced magnetic field has been calculated. For circular coil with unilateral bending along the lines located 0.5cm, 1cm and 1.5cm apart from the center, the best bending angles are 60°~90°, 60°~105° and 75°~105°, respectively. For figure-of-eight coil with bilateral bending along the lines located 0.5cm, 1cm, 1.5cm and 2cm apart from the center, the best angles are 90°~120°, 90°~120°, 105°~135°and 120°~150°,respectively.In order to get the relatively ideal stimulation depth and focality, coil array based on figure-of-eight coils has been designed and the performance of coil array has been analysed by numerical method. Results show that the stimulation depth and focality have been improved obviously when one of the coil groups direction of current flowing is reverse to the other coil groups. When the coil groups bending with different angles, the best distance can be obtained for the ideal stimulation depth. When the distance from the coil array array plane is a fixed value, the best bending angles and the best coil array can be achieved by the analytic of stimulation depth and focality.