Microwave Thermally Induced Ultrasound Imaging Study

The medical statistic results show that the number of cancer patients is growing every year, and the pre-detection to the early-stage cancer is very important to the therapy effect. So, the research of the technologies for pre-detection is critical. Now, there are three main detection methods, X-ray tomography, Ultrasonic tomography and NMR (Nuclear Magnetic Resonance). All these methods have their own defects. X-ray has some damages to the human body and the imaging results for the weak absorbers are not good, therefore it is not easy to detect the early-stage cancer. Although, the Ultrasonic tomography has high resolution, it has poor contrast in imaging results due to its reconstruction mechanism. The NMR technology can not distinguish the benign cancer and malignant cancer well.The MITAT (Microwave Induced Thermo-acoustic Tomography) is a new detection method. It uses the microwave pulse to irradiate the tissue and the tissue transforms the absorbed electromagnetic energy into thermal energy. Because different parts of the heterogeneous tissue experience different thermal expansion, thus producing different acoustic waves that can be collected to reconstruct the tissue. Because it uses microwave for irradiation while ultrasonic for reconstruction, it has excellent resolution and contrast. So, MITAT is a promising technology.The thesis is mainly on the research of the MITAT system in both theories and experiments. They can be summarized as:1. The theory of the MITAT technology has been researched. The factors which affect the thermo-acoustic signal have been analyzed. The magnitude of the induced thermo-acoustic signal has been estimated in theory and the system's safety has been evaluated as well.2. The MITAT system has been successfully developed by our group. The system experienced several stages; the electromagnetic compatibility has been improved. The performance of the system with different coupling material, experimental container and amplifier, et al, has been investigated.3. The cascade system theory has been applied to interpret that the frequency feature of the energy distribution of the experimental data will be affected by the tissue figure. The resolution of the system has been discussed with the simulated data. Wavelet soft-thresholding method has been first time used to analyze the MITAT signals. The results showed that this method can greatly improve the SNR of the MITAT signal.4. Some reconstruction methods, such as FBP (filtered back-projection) method and frequency domain reconstruction method, have been researched based on the experimental data obtained by the developed MITAT system. In order to increase the efficiency and improve the resolution of the system, NUFFT (non-uniform FFT) technology has been adopted. The frequency domain reconstruction method (named wavenumber domain as well) which is based on NUFFT has been first time proposed in the imaging of MITAT signal. The reconstructed results showed that the resolution of the present system can be up to the order of mm.