Design And Implementation Of Photoacoustic Imaging Acquisition System

Photoacoustic imaging developed in recent years is a novel technique of noninvasive medical imaging; it gets the benefits from combining the high contrast of optical imaging with the great resolution of ultrasound imaging. And it has the outstanding advantages in researching structure of biological tissues, metabolism function and physiological characteristics and has the potential biomedical application. With great interest in the potential applications, it has gradually become the hot research toptic in the field of medical imaging.This dissertation first introduces the principle of photoacoustic imaging and frequently-used photoacoustic imaging systems and the disadvantages of the current photoacoustic imaging syetems are analyzed. The current imaging systems have poor stability and reliability due to the mechanical movement and can not achieve real-time imaging for its long acquisition time. Adopting broadband linear array ultrasonic transducer to detect the photoacoustic signal, the photoacoustic imaging acquisition systems designed in this dissertation can collect all the data required for a whole image without moving the transducer or samples, so this acquisition system enhances the stability and reliability of the photoacoustic imaging system.Photoacoustic signal acquisition is one of the key techniques in photoacoustic imaging equipments. In order to slove the issue of large amounts of acquisition data and difficult transmission, this dissertation designs the FPGA+SRAM+USB+PC data acquisition and transmission scheme, FPGA worked as the main controller in this scheme to read A/D sampling data and store them in SRAMs before the sampling data are transmitted to PC through USB. Two SRAMs within this system are employed with a ping-pang caching type to ensure that a high data transmission speed can be achieved. Also, to ensure the accuracy of data transmission, USB operates to transmit the data to PC under the Slave FIFO mode of automatic synchronization of data transmission. The control timing in FPGA for the Slave FIFO and ping-pang buffer is designed, the firmware of USB chip is programmed, and the application program which is used to transmit data between PC and USB and display the acquired images in PC is accomplished.Image reconstruction algorithm is another key technique in photoacoustic imaging; it is efficient and can improve imaging resolution and imaging speed. The filter back-projection reconstruction algorithm commonly used in photoacoustic imaging can produce artifacts and reduce the imaging resolution. Another frequently used anti-convolution reconstruction algorithm can eliminate reconstruction artifacts and improve the reconstruction speed, but it has poor noise suppression ability. This dissertation completes the simulation of deconvolution reconstruction algorithm based on wavelet transform, which can not only enhance the noise suppression capability, but improve the imaging resolution without reducing the reconstruction speed.