Implementation And Evaluation Of MR-compatible Transcranial Direct Current Stimulation System

Transcranial Direct Current Stimulator(tDCS),as an effective non-invasive neuromodulation technology,has been widely used in clinical research on neurological and psychiatric diseases such as stroke rehabilitation and mental disorders.The research on the mechanism of tDCS and the optimization of treatment plan are the research hotspots in the field of neurohealth engineering.Magnetic Resonance Imaging(MRI),as a non-invasive imaging technology,has been widely used in brain science research.The combination of MRI and tDCS has been used to explore the mechanism of stimulation curative effect,which can provide a theoretical basis for clinical applications such as tDCS positioning and dose optimization.Based on the analysis of the development trend of the combined application of tDCS and MRI,according to the requirements of safety,equipment function,and imaging quality,the external and internal Magnetic Resonance compatible tDCS systems were designed and implemented respectively.In ordinary magnetic resonance application scenarios,the external magnetic resonance compatible tDCS system is preferentially used to effectively avoid bringing additional electronic equipment into the magnetic resonance scanning room.The external magnetic resonance compatible tDCS system is mainly composed of tDCS equipment,magnetic resonance compatible kit,and control terminal software;the magnetic resonance compatible kit includes carbon fiber electrodes and lead wires,shielded cables,and signal line filters.Carbon fiber electrodes and lead wires have little eddy current effect in a high-intensity magnetic field and will not produce imaging artifacts,so their performance is better than traditional metal rubber electrodes.The π-type filter implements two-way radio frequency filtering,thereby reducing electromagnetic interference introduced into the scanning room,and at the same time preventing the radio frequency electric field from damaging the function of the tDCS equipment.When combined with other brain observation devices,the built-in magnetic resonance compatible tDCS system is used.The tDCS equipment can be placed in the magnetic resonance scanning room and integrated with other devices.The built-in system tDCS equipment has magnetic resonance compatibility.The specific design includes the selection of magnetic resonance compatible electronic components,the design of magnetic resonance compatible communication methods(wireless or optical fiber),and the overall electromagnetic shielding design of the equipment.The built-in magnetic resonance compatible tDCS system can have the functions of an external system,and it can also be easily integrated with other magnetic resonance observation equipment,thereby reducing the stray magnetic field introduced by a long cable and improving the quality of magnetic resonance imaging;but its design is more complicated.In order to verify the magnetic resonance compatibility of the tDCS system,this study carried out a systematic evaluation from multiple aspects such as safety,equipment function,and imaging quality.The results show that the maximum temperature rise caused by the eddy current effect of the carbon fiber electrode is 1.5℃,which is the normal range of local temperature rise on the skin surface,and there is no redness,swelling or burn on the tested skin surface,which meets the design safety.The tDCS system can be used normally in a magnetic resonance environment,the current is adjustable within 0～2mA,and the output current accuracy is less than 0.1mA;the safety current detection accuracy and the electrode contact impedance detection accuracy are both less than 5.0%.Using a 3T magnetic resonance scanner,the impact of the MR-compatible tDCS system on the imaging quality was tested under three conditions(only the connected electrode equipment does not work,the equipment works,and the equipment removed).Experimental results show that under the three conditions,there is no significant difference in the signal-to-noise ratio of the hexagonal prism water model imaging.This study further carried out a 7T magnetic resonance experiment using rhesus monkeys,and verified that the magnetic resonance compatible transcranial direct current stimulation system had no significant effect on the uniformity of the high-intensity static magnetic field and the radio frequency coil.At the same time,the macaque was scanned for structural images,and there was no imaging artifacts caused by the stimulation electrodes in the imaging.