Research And Implementation Of High Definition Transcranial Electrical Stimulation Based On Real Head Model

Transcranial electrical stimulation(t ES),a non-invasive brain stimulation technique,has greatly promoted and expanded brain science-related research in recent decades with its advantages of low cost,non-invasiveness and high safety.High-precision electrical stimulation(HD-t ES)has become the most widely used multi-electrode topology in clinical applications due to its better target stimulation performance and stimulation effect.Passive HD-t ES,as the mainstream technical form of HD-t ES,has a unique multi-passive return electrode with multi-channel imbalance problem,which makes the target area field distribution with uncertain errors.Meanwhile,as the operating frequency of t ES has been expanding from DC to tens of k Hz,the dose setting and field distribution assessment of the current study is based on the DC model without considering the field distribution errors caused by the frequency-dependent characteristics of tissue conductivity.In addition to dose limiting and stimulation protocols,impedance on-line monitoring techniques are recognized as a means to ensure safety during stimulation,but current impedance on-line monitoring methods have limitations in measurement accuracy and application scope.Based on this,the research in this paper will carry out simulation modeling study on the multi-channel imbalance error and frequency-dependent error in HD-t ES field distribution consistency problem based on the real head model,and carry out modeling analysis and experimental study for the electrode impedance online monitoring technique.The consistency of the simulated field distribution is closely related to the stimulation dose setting,field distribution assessment and experimental results analysis in transcranial electrical stimulation.In this paper,we will quantitatively investigate the multi-channel imbalance problem of passive HD-t ES and the frequency-dependent error of wide-frequency domain HD-t ES based on a five-layer real head numerical computational model.Firstly,a five-layer head(scalp,skull,cerebrospinal fluid,grey matter and white matter)grid model was obtained by morphological segmentation and post-processing of the MRI data to reconstruct the model.Further,the target area electric field intensity JRE and vector focality Fc were established for quantitative evaluation of the field distribution changes in the target area.On this basis,the impact on the evaluation metrics is simulated and analysed for the multi-channel imbalance problem caused by impedance network shunting in passive HD-t ES and the frequency-dependent error caused by the tissue conductivity characteristics in widefrequency domain t ES.In order to realise the online monitoring of safety during stimulation,this paper proposes an impedance online monitoring method based on the current perturbation method.Firstly,the difficulty of online monitoring of multi-electrode impedance is illustrated by means of a collector circuit model,and the conditional linear effect of electrode impedance is proposed and verified.Based on this,the individual electrode impedance of the active HD-t ES is solved and a matrix for calculating the impedance that can be used for any multi-electrode topology is established.Finally,impedance on-line monitoring and fault identification experiments are carried out to verify the correctness of this method and also provide new ideas for impedance on-line monitoring of multi-electrode topologies.To support the experimental study of multi-channel imbalance and impedance monitoring,a modular HD-t ES system is developed,including: the main control circuit,digital-analogue and constant current source circuit,conditioning and sampling circuit,lithium battery charging and discharging circuit and multi-track power supply circuit.The hardware implementation will be explained in terms of requirement analysis,device selection and schematic design.This is followed by the implementation of the system software,including waveform control and impedance monitoring.Finally,the constant current source module and the conditioning and sampling module are tested for accuracy,and the waveform control and impedance monitoring functions are verified.