实用化EIT条件下不同激励模式成像效果仿真研究

Study on Imaging Effect of Different Excitation Patterns under Practical Electrical Impedance Tomography Conditions

目前常用的电阻抗断层成像(EIT)相邻激励-相邻测量模式下,有限测量分辨率(MR)和信噪比(SNR)的系统往往难于分辨微小电位差,影响图像重建。通过获取16电极EIT系统均匀场在相邻、间隔6电极和相对激励模式下的理想仿真边界电压,分析实用化EIT系统成像对MR和SNR的要求,仿真模拟了不同MR和SNR测量条件下3种激励模式对近场域中心目标A、场域1/2半径处目标B、近场域边缘目标C的成像。图像重建采用Tikhonov-Noser组合正则化算法,引入图像重建误差函数和结构相似度函数定量评价成像效果。结果表明,各激励模式对不同目标成像要求的MR和SNR不同。MR为1 m V和0.01 m V时,成像效果分别是间隔6电极激励和相邻激励最优;MR为0.1 m V时对模型A、B成像间6激励更优,对模型C成像相邻激励更好。间隔6电极和相对激励对模型A、B、C成像要求的SNR临界值分别为50、40和30 d B,都比相邻激励低10 d B,临界值附近间6成像效果最优,其次是相对激励,SNR高于临界值10 d B时相邻激励成像质量最高。低MR和高MR时影响成像的主要指标分别是各模式边界电压次小值与最小值之差和独立测量数。建议低MR成像时优先选择间6激励,其次是相对激励,高MR时选择相邻激励,MR为0.1 m V时近场域边缘目标成像选择相邻激励而近场域中心目标成像选择间6激励。低SNR和高SNR时影响成像的是测量电压数组整体的数值大小和独立测量数。模型A、B、C成像时若SNR分别在50、40和30 d B的临界值附近建议选择间隔6电极和相对激励,一旦SNR高于临界值10 d B,建议选择相邻激励。

Using the commonly used adjacent excitation pattern-adjacent measurement pattern in the electrical impedance tomography（ EIT）,the practical detection system with finite measurement resolution（ MR） and signal-to-noise 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 Tikhonov-Noser regularization algorithmwas 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 was1 m V,the imaging effect of interval 6 electrodes excitation pattern was the best,while adjacent excitation pattern was the best when MR was 0. 01 m V. When MR was 0. 01 m V,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 d B,40 d B,30 d B respectively under the interval 6 electrodes and opposite excitation patterns,which were 10 d B 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 m V 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 d B,40 d B and 30 d B 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 d B.