Experimental study of thermoacoustic imaging system.

摘要

Thermoacoustic Imaging is a relatively new medical imaging modality, which combines the benefits of pure microwave imaging and conventional ultrasound imaging, achieving both their high image contrast and high spatial resolution respectively. In operation, the soft tissues in the imaging area are exposed to microwave pulses with a high peak power. Upon irradiation, the tissues will absorb the electromagnetic energy, expand in volume and generate a thermoacoustic signal propagating in all directions. A transducer system picks up the generated thermoacoustic signal, which is then amplified, digitized, and transferred to the computer. An image reconstruction program running in the computer solves an inverse problem to obtain the image of the microwave absorption distribution inside the tissue. Cancerous tissue has a relatively strong electromagnetic absorption due to its higher water content [1], and distinguishes itself from other tissues in the image.;An experimental study of the thermoacoustic imaging system is performed in this thesis, which includes building the prototype system, conducting the initial experiments for generating thermoacoustic signals, and obtaining images of different phantoms with this system. At the beginning, CW (Continuous Wave) microwave stimulation was employed to find the resonance of the phantom, and finally failed for various reasons. Then pulsed microwave radiation was used, and successfully generated the thermoacoustic signal. A single transducer, coupled with a motor system, was used to simulate a multiple transducer array for data acquisition. Based on the time-delayed Robust Capon Beamforming (RCB) algorithm, several images were acquired from different phantoms.;A Field Programmable Gate Arrays (FPGA) device was used to investigate a hardware implementation of the RCB algorithm. Two implementations were achieved, with one realizing the narrowband RCB used in smart antenna systems and another realizing the wideband RCB used in medical imaging. The possibility of making the thermoacoustic imaging system run in real-time is studied in this work.