System Design And Algorithm Research For Multi-frequency Electrical Impedance Tomography

Multi-frequency Electrical Impedance(MFEIT)is a new detection technique for medical imaging,which has gained rapid development in rencent years.It injects multi-frequency current in human body and acquires induced voltage mearement to reconstruct inner impedance distribution,which has advantages such as non-invasion,rapid response,non-invasion and low cost.Compared with traditional EIT using single frequency,MFEIT can extract more physiological and pathological data through impedance distribution under multiple freuqncies.In order to sovle the problem that the current MFEIT systems can not acquire the accurate phase measurement,a new MFETI system based on the reference signal measurement method was designed and comprehensive test and imaging experiments have been finished.Moreover,algorithm research has been developed based on this system.(1)A hardware platform based on the “main board and switch board” method has been designed to realize the channel switch circuit to adjust the electrode status easily;a high-accuracy multi-frequency current source with adjustable output frequency and amplitude as well as high output impedance was designed using the differential current mirror topology;a high precision resistor was put in series with the load through which both the phase data and amplitude data can be calibrated to further improve the accuracy of the system based on the reference signal;the signal process and acquisition circuit contains the signal pretreatment circuit,the programmable gain amplifier and the analog-to-digital conversion circuit,it can realize high precision measurement.(2)Complete experiments have been carried out to test the MFETI system through simulation and real test.The signal-to-noise ratios(SNRs)of both the amplitude and phase measurements have been calculated.The model imaging experiment has been finished and the results of biological tissues have been analysed and confirmed.(3)Aimed at the low accuracy problem in the solution of weighted frequency difference(WFD)method,the Tikhonov regularization was introduced to improve WFD method,and the parameter selection based on the L curve method and the property of corners of L curve were discussed.(4)A new regularization method based on the total differences of neighbors(TDN)was proposed to overcome problems of traditional regularization methods such as the blurring of edges,the bad noise immunity as well as the error of reconstruction of square objects,and an improved image reconstruction method was given accordingly for the detection of square object.