| Breast cancer is one of the most common malignant cancers threatening women’s health and life. Early detection and treatment is an important approach to decrease the mortality rate. The detection accuracy has been greatly improved by the current breast cancer detection technologies, such as, mammography, ultrasound, MRI, etc. However, the current technologies have the problems of radioactivity, dependence strongly on operators and expensive equipments, which cannot satisfy the clinical needs of extensive screening of early-stage breast cancer. Breast electrical impedance scanning(EIS), which is a new modality of breast cancer detection technology, has advantages of low-cost, noninvasive, non-radiative, easy to operation and providing functional image. It is sensitive to early-stage cancer and has a promising prospect in screening of the early-stage breast cancer, and now it’s in the stage of clinical research.EIS detects breast cancer by the significant differences of electrical impedance between cancer tissue and normal tissue. EIS acquires the electrical impedance distribution inside the mammary tissue by measuring the current on the surface of breast. However, when measuring the electrical impedance of breast, the impedance of electrodes-skin interface is also included and the two are aliased together due to the static imaging property. So, the characteristics of electrode-skin interface is closely related to measuring the electrical impedance of breast. The domestic and international researchers have been focusing on the optimization design of electrode-skin interface. The application of EIS to screen early-stage breast cancer was firstly proposed by our group, and much higher requirements such as detection rate, stability and operating easily have been put forward. Thus to systematically research the characteristics of electrodes-skin interface in EIS has important meaning both in theory and clinical applications. The main research including:(1) Simulation studies of the characteristics and effects of electrode-skin interface in breast EISThe structure of the electrode-skin interface consists of skin tissue, coupling layer and electrodes array. The main characteristic of electrode-skin interface in EIS is its impedance. Firstly, based on the equivalent circuit model, the relationship between the influence of the three key characteristics(the value and the homogeneity of electrode-skin interface impedance(ESII), and the conductivity of coupling layer) and the breast EIS imaging has been analyzed. Secondly, the relationship between the conductivity of coupling layer and the detection ability of EIS, the degree of signal crosstalk between the electrodes has been studied, and the results demonstrated that the reference value of the conductivity of coupling layer is 0.35 S/m~0.8 S/m when simulating the real situation, which provided basis for choosing the new material of coupling layer in the next step. Finally, the features of the imaging artifacts caused by local anomalies from electrode-skin interface has been studied, which provided theoretical basis for recognizing and verifying artifacts in the next step.(2) Studies on the methods of improving the properties of electrode-skin interfaceBased on the simulation studies, three types of ionic membrane material(DSICM-A, DSICM-B & DSICM-C) have been designed to form three novel electrode-skin interfaces. Comparison tests of the DSICM-A, DSICM-B & DSICM-C interfaces, the present ultrasound gel interface and the CFGTL(Cotton Fine Grid Thin Layer) interface have been conducted. Firstly, electrode-skin interface impedance(ESII) under the five interfaces was measured in-vivo by four-electrode derivation method. Compared with CFGTL interface, ESIIs of the new designed three types decrease 20%~25% and their stability are higher. Then, the imaging qualities of EIS under the five interfaces was compared by clinical test. The results showed that the property of DSICM-C interface was optimum, and the mean value of measured data increased more 10.8% than the CFGTL interface, the data dispersions inside single frame decreased by 9.2% and the repeatability of multiple frames increased by 24.1%(3) Studies on methods of suppress image artifacts caused by local anomalies of electrode-skin interfaceLocal anomalies of electrode-skin interface can induce image artifacts and influence on the detection results. Two artifact-recognition methods, two-way gradient analysis method and singular value decomposition(SVD) method, have been proposed based on simulation. The two methods were verified via simulation data and clinical experimental data. The study showed that artifact information in simulation data could be recognized accurately by the two methods. The recognition rate of artifacts improves from 65.0% to 87.6% in the clinical data when combined the two methods. Finally, an artificial correction method based on SVD was proposed, the results showed that the image quality improves further both in simulation data and clinical data.(4) Study of improving the properties of electrode-skin interface by broadening the frequency spectrum of breast EISStudies demonstrated that broadening the frequency spectrum not only can help improve the properties of electrode-skin interface in EIS, but also can provide more electrical impedance spectrum information about the breast tissues for EIS. In order to increase the highest frequency from 200 k Hz to 500 kHz, the detection module and signal acquisition module were designed. Firstly, a new method of the detection module suitable for high frequency detection has been designed, and the operational amplifier(OA) AD4637 and the SPDT multiplexer was tested and chosen. Besides, a method for 4-channel A/D acquisition module was designed. This part has made the foundation of the improvement of EIS hardware system in the future.In conclusion, based on the simulation studies, a coupling layer material of better performance which could effectively improve the performance of electrode-skin interface has been designed. Besides, methods for detecting and correcting the imaging artifacts caused by local anomalies of electrode-skin interface have been proposed, which has suppressed the influence of the artifacts effectively. Aiming at spreading frequency of breast EIS hardware system, an exploratory research has been done which has improved the performance of electrode-skin interface further. |
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