Microwave-Induced Thermoacoustic Imaging For Early Breast Cancer Detection

As the incidence of breast cancer rises continuously, early breast cancer detection becomes more and more important. Microwave-induced thermoacoustic imaging and detection, implemented by transmitting microwave pulse to irradiate the breast tissue and acquiring the induced ultrasound wave from the tumor, has attracted more and more attention for early breast cancer detection due to its high imaging resolution and high imaging contrast.In this dissertation, the theory of microwave-induced thermoacoustic effect for early breast cancer detection is introduced, and some problems such as microwave irradiation of breast cancer, thermal conduction and the propagation of thermoacoustic signals in the breast are investigated. The microwave-induced thermoacoustic effect of breast tumor is simulated by using our FDTD codes and the induced thermoacoustic signal is calculated. For tumor detection and imaging, the confocal imaging algorithm is employed and the thermoacoustic image reconstruction verifies the millimeter resolution as desired.Moreover, some practical problems occurred in microwave-induced thermoacoustic imaging for real breast are further studied based on the numerical simulation and imaging. The simulation results show that the induced thermoacoustic signal of tumor is not only related to its size and shape, but also to the frequency, duration and polarization of the microwave pulse irradiating the breast. Multi-polarized irradiation will benefit the detection and imaging. As for the choice of the microwave irradiation frequency, the trade-off must be made in order to insure the penetration depth of the microwave signal, imaging contrast and signal-to-noise ratio. Besides, the microwave pulse duration on the imaging resolution is also studied and it turns out that microwave pulse with longer duration will lead to poorer imaging resolution. For real breast survey with non-uniform distribution of microwave energy in the breast, possible miss of the breast tumors in imaging when there are many tumors in the breast can be solved by using several local irradiation and imaging. Our study on the effects of the acoustic heterogeneity of the breast indicates that a ± 5% variation of the acoustic speed in the breast will not do harm to the tumor reconstruction.