Coil Design And Magnetic Measurement For Small Animal Transcranial Magnetic Stimulation (TMS)

Transcranial magnetic stimulation (TMS) is a noninvasive, focused and non-invasive stimulation techniques of the brain, which has good temporal resolution and spatial resolution. In these years, TMS has been widely used in diagnosing and curing diseases and the scientific research of the brain, a lot of achievements have been achieved though these studies. Some studies have shown that most of the TMS experiments of the human brain can be profound in the small animal experiments, and then compare the macroscopic signals such as EEG and EMG with the microcosmic information such as synaptic plasticity, the membrane potential and neurotransmitters flow, thus to discuss the mechanism of TMS. However, due to the different size between human brain and the small animal brain, the focus ability and the targeting of the universal TMS coil can not satisfy the TMS experimental studies of small animals. In current TMS experiment studies of small animals, the magnetic field shows a worse focus ability, the coils couldn’t be applied to specific brain regions accurately, which caused difficulty in studies of TMS mechanisms. Therefore, special coil design for small animals is really important in studies of TMS effects and mechanisms.In this thesis, a head model of six layers has been built using the rat (including scalp, skull, CSF, gray matter, white matter and deep tissues). The eight-figure coil and cone-shape coils with different angles of 160°,140°,120°,115°,110° 105° and 100° were set up by the ANSYS FEM software. For the eight-figure coil and 110° cone-shape coils, the radius was further changed to 5mm,8mm and 11mm. The distribution of magnetic fields and the induced electric fields are calculated numerically. Results showed that eight coil has a better focality of the magnetic fields and the cone-shape coil has a stronger induced electric fields. When the radius of the coils become smaller, the focality of the magnetic field has been improved. Synthesizing the focality and the intensity of the induced electric fields, we think the cone-shape coil with the angel of 110° and a small radius has a good performance, especially in the deep tissues. Therefore, according to the simulation results, the optimal angle of the cone-shape coil is 110° and the optimal radius is 5mm.To detect the magnetic field dynamically, we set up a dynamic detection platform for the microsecond pulse weak magnetic field, as well as the calibration device. The magnetic field detection circuit mainly includes high-speed, stable signal amplifier, signal filtering and signal integration module. This thesis also tested the magnetic field detection accuracy. Results showed that the measured values were basically consistent with the value of commercial fluxmeter.In addition, the optimized coil was made and packaged, and the magnetic field of the coil was measured by the self-design magnetic field detection platform. Results in this thesis would provide certain basis for coil design of small animal TMS, and promote studies of TMS effects and mechanism.