The Research Of Thermoacoustic Tomography For Medical Applications

At present in clinical medicine the most widely used medical testing means areX-ray imaging, magnetic resonance imaging(MRI), ultrasound imaging, radionuclideimaging. For these commonly used medical detection methods have their ownlimitations, new medical imaging technologies have attracted a lot of attention.Microwave induced thermoacoustic tomography(TAT) is a new imaging method,which made the tissue under the irradiation of the microwave pulses, and the tissuewould absorb the energy to generate acoustic waves by thermoelastic expansion. Theacoustic waves could be received by the ultrasonic transducer and recorded by computer.And then the recorded data can be used to reconstruct the image of the tissue by someimage reconstruction algorithms. The above is the main principle of the microwavethermal acoustic imaging. This technology inherits the characteristics of high-resolutionultrasound imaging and high-contrast thermal acoustic imaging. And the microwavealso have deep penetration depth in the human body, for that it is more suitable for deepimaging, thus in the field of medical imaging, it has great potential for development inthe early detection of breast cancer and the functional imaging of brain.This article mainly focuses on the research of image reconstruction algorithm andthe experimental studies of termoacoustic tomography imaging. The main contentsinclude the following aspects:1. The research background and the current status of TAT. First the four commonlyused detection means in clinical medicine was introduced, and the pros and cons, therange of applications of each method was also discussed. Then according to the currentsituation of the medical testing, the advantages and characteristics of TAT was discussed.At last we introduced the research achievements of both the domestic and foreignexperts in two aspects of the imaging theories and experiment systems.2. The theory research of TAT. We discussed the process of TAT in three aspects,including the propagation of electromagnetic waves in tissue samples, transmission andattenuation of ultrasound in the tissue, and thermoacoustic signal generation process.These analyzes laid the foundation for the research of image reconstruction algorithm and experiments.3. The research of image reconstruction algorithm. The delay and sum algorithm,the time reversal algorithm and the finite element-based reconstruction algorithm wereintroduced. Then we compared the three algorithms by using a set of experiment datafor image reconstruction. At last we proposed a new image reconstruction algorithmwhich is based on genetic algorithm, and by simulation we confirmed the feasibility ofthe algorithm.4. The research of the experiment system. The3GHz circular scanning microwaveinduce thermoacoustic tomography imaging system was set up by us, and theperformance and parameters of the system components was described in detail.5. The experiment research of thermoacoustic tomography. First the influencingfactor of thermoacoustic tomography was analyzed by the experiment means, includingthe imaging depth, the size of the sample, the scanning step, the scanning range and thesalt content of the sample. Then we did the experiment of imaging the breast tissue exvivo. At last the in vivo imaging experiment of the tumor in the body of a nude micewas done, and we also compare the reconstruction image with the photoacoustictomography result.