Research On Phased Array Imaging Algorithm For Endoscopic Ultrasound

Medical ultrasonic endoscope sends the micro ultrasonic probe and electronic en doscope front-end into the human body together. The doctor can observe the surface o f the digestive tract with electronic endoscope and the internal tomography informatio n with ultrasound scanning at the same time. So it is one of the most effective ways to find the gastrointestinal diseases.However, the imaging system of mechanical rotating ultrasonic endoscope has a low system resolution and its scanning direction is inconsistent with the observation direction of electronic endoscopic, so it is not suitable for the clinical treatment, such as puncture. We firstly presented a new chirp-coded phased array imaging algorithm(CPAI) using phased array transducer for Endoscopic Ultrasonography in this dissertation. The algorithm uses the steering beam to scan the human tissue, takes advantage of the synthetic aperture imaging technology which picks out the coherent samples of the recorded echoes and sums these samples and the technology of the modulated excitation signals to enhance the SNR and resolution. Because this algorithm sets high demands on processing capabilities, the technology of the parallel computing of the general-purpose graphic processing units(GPU) is used to accelerate the CPAI from the hardware.The main points of this dissertation are shown as follows:1) Study the influence of various transducer parameters on the beam steering properties, including number of elements, inter-element spacing, element size, frequency of the transducer and the steering angle. In addition, the effects of these parameters on the acoustic pressure in the steering direction are studied. At last, a suggested scheme for optimal transducer design is presented.2) Present a phased array imaging algorithm(PAI). The algorithm applies the focused image lines as input data, and take advantage of the synthetic aperture imaging technology which picks out the coherent samples of the recorded echoes and sums these samples. PAI is dynamically focused in both transmit and receive yielding an improvement in resolution.3) Present a chirp-coded phased array imaging algorithm(CPAI). The algorithm uses chirp-coded excitation, and use the PAI process the scanning data after the pulse compression for enhancing the robustness of the algorithm and improving the resolution of the system.4) Study the parallelism of CPAI, and present a software architecture based on the mixed use of GPU's CUDA and the MATLAB. Finally accelerate the CPAI from the hardware.5) Construct an experimental system of endoscopic ultrasonic phased array imaging with a 16-element transducer whose aperture size is 2.32 mm to implement multi-point targets experiment. Finally verify the feasibility of the phased array imaging algorithm and the experimental system.