Study on Imaging Effect of Different Excitation Patterns under Practical Electrical Impedance Tomography Conditions
1 Institute of Biomedical Engineering, Chinese Academy of Medical Sciences & Peking Union Medical College, Tianjin 300192, China
2 No.291 Hospital of People〖DK〗’s Liberation Army, Baotou 014040, Inner Mongolia, China
Abstract：Using the commonly used adjacent excitation patternadjacent measurement pattern in the electrical impedance tomography (EIT), the practical detection system with finite measurement resolution (MR) and signaltonoise ratio (SNR) is always limited to distinguish tiny potential difference of electrodes and then finally make a great impact on image reconstruction. Based on the homogeneous field EIT boundary voltages analysis of adjacent excitation pattern, interval 6 electrodes and opposite excitation pattern in 16 electrodes array system, the MR and SNR requirements for imaging by practical EIT systems were analyzed, images reconstruction of three excitation patterns under different MR and different SNR conditions were simulated for three different image models A, B, C, which are positioned near to the center of the field, at the 1/2 radius of the field and near to the edge of the filed respectively. The combined TikhonovNoser regularization algorithm was adopted and image reconstruction errors function and structure similarity degree function for medical images quality evaluation were introduced to quantitative analysis the imaging effect. Imaging and evaluation results show that different excitation patterns have distinct index requirements of system MR and SNR. When MR was 1 mV, the imaging effect of interval 6 electrodes excitation pattern was the best, while adjacent excitation pattern was the best when MR was 0.01 mV. When MR was 0.01 mV, interval 6 electrodes excitation pattern was better than the adjacent excitation pattern for model A and B while the circumstance is opposite for model C. The critical value requirements of system SNR for Model A, B, C were 50 dB, 40 dB, 30 dB respectively under the interval 6 electrodes and opposite excitation patterns, which were 10 dB lower than the adjacent excitation pattern when imaging for all three models. The best imaging effects of all three model were under interval 6 electrodes excitation pattern when these SNR values near to critical values, followed by opposite excitation patterns. However, once the value of SNR was higher than the critical value, the best quality image was obtained under the adjacent excitation pattern. The main indexes impacting imaging results in low MR system and high MR system were different between the second smallest voltage and the smallest voltage and independent measurement number. It is advised to take interval 6 electrodes excitation pattern as the priority selection and opposite excitation pattern as the second one when system MR is relatively low, while choose adjacent excitation pattern when MR is high. For the 0.1 mV MR, interval 6 electrodes excitation pattern is suggested when imaging for model A and B and adjacent excitation pattern is suggested for model C. The factors impacting imaging results in low and high SNR system are the result of whole measurement voltage data and independent measurement number. When values of the system SNR are near to the critical values of 50 dB, 40 dB and 30 dB for model A, B, C respectively, interval 6 electrodes and opposite excitation pattern are suggested, and the adjacent excitation pattern is suggested once SNR exceeds critical value 10 dB.
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