| Transcranial magnetic stimulation(TMS)is a technique for non-invasive stimulation of the human brain,which is being extensively studied and rapidly developed currently.TMS uses a pulse current to excite the TMS coil to generate a TMS pulsed magnetic field,thereby inducing an induced electric field in the area of brain below the TMS coil.The biological currents are generated by the induced electric field in the brain and conduct in the tissues,which change the motor potentials of cortical neurons,and affecting brain metabolism and neural activity ultimately.In current research of the TMS,most studies use the head models to simulate the strength,focus and depth of penetration,so as to optimize the structure of the TMS and parameters of the excitation source,but there are very few studies and evaluations on the actual TMS magnetic field generated by TMS devices.The current research on the TMS magnetic field mainly uses the head model to simulate the magnetic field strength,focus,depth,etc.,so as to optimize the structure of the TMS coil and the parameters of the excitation source,but there are very few studies and evaluations on the actual TMS magnetic field.Due to the deviations between reality and theory,the simulated results cannot completely replace actual results.Therefore,it is very important to detect and evaluate the actual TMS magnetic field before biological experiments and clinical treatment to improve the safety and reliability of TMS.In this thesis,a 264-channel high-performance TMS magnetic field detection system is designed to complete the pre-detection of TMS magnetic field.In this thesis,different magnetic field detection methods are analyzed and a magnetic field measurement sensor is designed to acquire magnetic field signals.After assessing the actual requirements of the system,the scheme of TMS magnetic field detection is determined.The hardware design,control method,data flow transmission process and synchronization analysis of data acquisition(DAQ)card are described in detail.The thesis also involves the hardware acceleration design of the filtering algorithm,which improves the real-time performance of filtering greatly and solves the bottleneck of the system in terms of data processing speed.At the same time,some standardized evaluation methods are adopted to evaluate the performance of the system in many aspects to ensure that the system has outstanding advantages in both function and performance.This dissertation introduces the design scheme of the entire magnetic field detection system in detail,including the magnetic field acquisition system,the mathematical morphological filtering(MMF)hardware acceleration and the performance evaluation of the magnetic field detection system.The three-dimensional magnetic field detection sensor array is arrayed by induction coils according to the structure of the human brain,which can convert TMS pulsed magnetic field into induced electromotive force signals.The DAQ card can achieves the synchronous acquisition of 264 channels,the maximum sampling rate can reach 4 MSps/ch,and the resolution is 14 bits.Through the calibration of the DAQ card,the average signal noise and distortion and crosstalk of the channels can reach 65.1 d B and-83.4 d B respectively.On the DAQ card,field programmable gate array is used to perform hardware acceleration of MMF of the EMF signal of each channel,and the acceleration effect can reach about 445 times of the PC,realizing real-time filtering.The monitoring software is developed in Qt Creator 5.12 to process,display and backup data.Experiments show that the mean relative error of the magnetic field detection system is 2.19%,which is suitable for the calibration of various TMS devices,and has outstanding advantages in multi-channel,real-time,synchronization,dynamic performance,data throughput,and data visualization. |
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