| Microwave induced thermoacoustic imaging method has well developed in recent years, which combines with the characteristics of high-resolution of ultrasound imaging and high-contrast of thermal acoustic imaging. And the microwave can give deep penetration in the tissue which means of great potential for development in detection of breast cancer and functional imaging of brain.This thesis mainly focuses on the research of factors that affecting the reconstruction of the image, and the experimental studies of thermoacoustic tomography imaging of osteoarthritis. Firstly, we discussed the theory studies of microwave induced thermoacoustic tomography imaging, including the propagation of electromagnetic waves in tissue samples, transmission and attenuation of ultrasound in the tissue, and the generation process of thermoacoustic signal. We also introduced thermoacoustic image reconstruction algorithms, such as delay and sum algorithm, k-wave transform algorithm and finite element-based reconstruction algorithm. These analyzes build the foundation of the research of image reconstruction and experiments studies.Secondly, we introduced the 3 GHz circular scanning microwave induced thermoacoustic tomography imaging system, described the preparation of phatom and the basic process of experiment. Experimental results indicate that the conductivity of different sample will result different contrast of thermoacoustic reconstruction image. The thermoacoustic signal of each scan position is different, because the distance between the ultrasonic sensor and the microwave absorbing material remains difference, the acoustic attenuation in different directions is also different. Muscle tissue experiment indicate that k-wave transform algorithm have better edges in reconstructed image compared with delay and sum algorithm.And then, matlab simulations indicate that different shapes of the sensor have different acoustic field distribution. As for semi-circular and hemispherical focus sensor, if the sample is not on the focus of the sensor, the reconstructed signals will make great difference. In the research, Tukey window function can be used in the compensation of acoustic attenuation, to reduce the leakage of signal spectrum caused by rounding error.Finally, we conducted experiments on bone and joints in vitro with the 3GHz microwave induced thermoacoustic imaging system. Conducted finger joint experiment and frequency-domain and time-domain analysis for thermoacoustic signal obtained at specific position. Based on the photoacoustic imaging system, we conducted experiments of mouse bone, and discussed the advantages of microwave induced thermoacoustic imaging and photoacoustic imaging. |
