The Design And Implementation Of Photoacoustic Imaging System Based On Galvanometer Scanning

Photoacoustic Imaging for different biological tissues excited by a specific wavelength laser has large differences in the optical absorption coefficients and then makes a radiation of different intensity ultrasound (photoacoustic signal). The optical properties of biological tissue and the distributions reflected in the photoacoustic signal have a close connection with the physiological structure characters of biological tissue. And the absorptions of biological tissue have differences, therefore by detecting the photoacoustic signal and then an image reconstruction can be understood to the physiological information of biological tissue, thereby providing an effective physiological state of biological information within the organization, metabolism and disease characteristics for the medical workers.The main contents of this thesis are based on the laboratory unit scanning photoacoustic imaging system. The implementation of photoacoustic imaging system based on the laser scanning was presented. The thesis firstly introduces the overall structure of the photoacoustic scanning imaging system which mainly includes galvanometer, conditioning circuit, data acquisition card and FPGA etc.,The application of FPGA in the system is also described. Secondly, through the FPGA control galvanometer deflection periodically, TLC7226 chip hardware circuit is used, and the software is employed to fit the laser light simultaneously. Then based on the development of the VC data acquisition card, according to experimental needs the photoacoustic signal data acquisition is provided, while FPGA also is used to controls data acquisition card with laser trigger. A simulation experiments is done to verify the sample collection function of the acquisition card. Then we start to design the temporal part of the photoacoustic conditioning circuit, and through the FPGA to control the gain circuit stable change according to different needs and at the same time to tie the laser light at different gain conditions of the built galvanometer scanning system experiment. Finally based on FPGA preprocessing, a wavelet transform and hilbert transform on the photoacoustic signal data were to reproduce the photoacoustic signal images. The reduction image through the image data processing of FPGA is basically same to the reconstruction image obtained by matlab processing.The ultimate goal of this thesis is to achieve the integration of FPGA-based photoacoustic imaging system. Based on FPGA controls, the laser light, galvanometer deflection, Conditioning circuit, data acquisition and image processing were completed.