Coil Design of Repetitive Transcranial Magnetic Stimulation System for Small Animal

Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive technique to stimulate the brain, nerve and muscle by electric fields that are generated from an excitation coil. rTMS offers potential benefit as a therapeutic treatment for a variety of neurological and psychiatric disorders. Although various rTMS schemes have been developed for clinical studies, there is a lack of the coil for generating localized magnetic field with enhanced intensity for rTMS in small animal. The aim of this study was to design a miniature stimulation coil for rTMS studies in small animal. First, a circular coil with iron-core for improving the penetration of the magnetic field was designed which was equipped with a water cooling apparatus to prevent from over heat. In addition, the shields of varied sizes and shapes were employed to localize the stimulation area which distribution was measured in a magnetic field recording platform using Hall effect probe controlled by 2D step motor. Our results indicated that copper plate of 1 mm thickness with proper opening can shield well and provide localized stimulation to elicit motor evoked potential (MEP). However, the shock wave generated by magnetic stimulation was enhanced during the shielding experiment which might elicit auditory startle reflex (ASR) instead of MEP. Thus, a better sound proof design to reduce the sound below 96 dB should be taken into consideration when design a shielded rTMS for small animal.