Thermoacoustic Imaging And Its Application In Breast Cancer Detection

Thermoacoustic imaging(TAI) is a non-ionizing and noninvasive imaging method,which combines the merits of high ultrasound imaging resolution with high microwave imaging contrast. In TAI, a short nonionizing microwave pulse irradiates tissues to induce a small temperature rise, which consequently causes thermoelastic expansion to generate TA signals. By using an image reconstruction algorithm, TAI can then recover the microwave absorption distribution inside the tissue and further distinguish abnormal areas from background normal tissues. On the one hand, there is a contrast up to 10:1between malignant and normal adipose-dominated breast tissues, and it is easy for microwaves to penetrate the whole breast for deep TA imaging. On the other hand, TAI also has the potential to sensitive detect finger joint diseases, brain hemorrhage and tumor. Thus, the potential of TAI for breast tumor, finger joint and brain diseases detection is investigated in this thesis.TAI for breast cancer detection is the main purpose of this study, the basic theory of TAI was introduced at first, especially the quantitative reconstruction algorithm for TAI. After that, in this dissertation, two sets of thermoacoustic imaging systems were developed, which named thermoacoustic tomography and ultra-short pulse based high resolution TAI. A combined MRI, photoacoustic imaging(PAI) and TAI triple-modality tumor detection method was also proposed. Finally, the feasibility of TAI for breast cancer, finger joint diseases, brain hemorrhage and tumor imaging is demonstrated via various experiments results.The main results are as follows:1. Two sets of thermoacoustic imaging systems were developed, which named thermoacoustic tomography and ultra-short pulse based high resolution TAI. A combined MRI, PAI and TAI triple-modality tumor detection method was proposed.2. A salt-in-gelatin phantom that simulate the dielectric properties of a variety of human soft tissues was proposed and cross-validated by measurement results. By using of phantoms, ex vivo mastectomy specimens and tumor-bearing mice, the possibility of our quantitative TAI method for human breast tumor detection was validated.3. A triple-modality scheme combined MRI, PAI and TAI was proposed and investigated, and we demonstrated its unique ability for in vivo cancer detection usingtumor-bearing mice. These results show that the tissue functional optical and dielectric properties provided by PA and TA images along with the anatomical structure by MRI in one picture make accurate tumor identification easier.4. A shaft drive-based data acquisition scheme and a shielding room was developed for ultra-short based high resolution TAI. The feasibility of the proposed ultra-short based high resolution TAI was investigated via high frequency TA signal generation and imaging experiments.5. The new application of TAI for finger joint diseases, brain hemorrhage and tumor imaging was explored. The TAI scanners for human finger and skull imaging were developed. With volunteer’s fingers and real human skull, we obtained the finger and skull-based brain hemorrhage and tumor mimicking tissues’ TA images for the first time. These initial studies suggest that TAI can be a good candidate for screening and diagnosing of finger joint diseases, brain hemorrhage and tumor.According to experiments and theoretical studies carried out in this dissertation,the feasibility of quantitative thermoacoustic imaging method for breast cancer detection before its clinical investigation is fully validated. Due to high imaging performance needs for the early detection of breast cancer, we proposed the combined MRI, PAI and TAI methods to improve the sensitivity and specificity of TAI, and ultra-short pulse based high resolution TAI technology to enhance the resolution and energy conversation efficiency of TAI, which are more clinical applicability. Based on the advantages of TAI, the potential applications of TAI for finger joints and brain diseases diagnosing are explored, which opening up a new fields for TAI.