Use of passive magnetic material of different shapes for Transcranial Magnetic Stimulation

Transcranial Magnetic Stimulation (TMS) is an FDA approved treatment for the Major Depressive Disorder. It is a painless, non-invasive method which also have therapeutic effects on several other neurological disorders. TMS utilizes a time varying magnetic field to induce electric field in the brain which causes depolarization of the neurons. Quadruple Butterfly Coil (QBC) is a focused TMS coil which has 25% less volume of stimulation in comparison to commercial Figure-8 coil, with comparable maximum electric field value. Passive magnetic shields of different shapes, permeability, and position have been explored along with QBC to further improve the focality. The results with the passive shields along with the QBC has been shown with the help of a heterogeneous head model at two positions: Vertex and Dorsolateral Prefrontal Cortex. It has been found that there is an improvement in the ratio of maximum electric field at the scalp to the maximum electric field at the brain. Although, no difference has been determined in the volume of stimulation, when permeability, angle or position of the passive magnetic material had been varied.