Research On Synthetic Aperture Technique For Endoscopic Ultrasonography

Medical ultrasound endoscope has been used broadly in clinical practice toexamine internal organs. Through rotary scanning in vivo by sending a microultrasound probe into coelom, one can obtain cross-sectional images to determinewhether or not the precancerous tissues are buried in the parenchyma. Therefore,Endoscopic Ultrasonography is one of the most effective ways for diagnosinggastrointestinal diseases.However, ultrasound has a divergent feature with power degradation during thepropagation in vivo, which leads to the deterioration of signal to noise ratio (SNR)and system resolution. A new synthetic aperture approach using single elementtransducer for Endoscopic Ultrasonography has been presented in this dissertation.The approach uses the rotation feature of single element transducer probe, andtransmits and receives the echoes at different time and locations during the rotaryscanning to equivalently synthesize a large aperture for enhancing the SNR andresolution.The main points of this dissertation are shown as follows:1、 Present the synthetic aperture approach and matched algorithm forEndoscopic Ultrasonography based on single element transducer probe.Achieve the reconstruction of synthetic aperture image according to thecoded and linear frequency modulated characteristics of the echoes.2、 Present a chirp-coded robust synthetic aperture (CRSA) approach. Theapproach uses chirp-coded excitation and pulse compression which havelarge Doppler tolerance to displace that of traditional Barker code forenhancing the robustness of synthetic aperture technique.3、 Implement the simulation and analyzation of CRSA, confirming therobustness by estimating the disturbance caused by sound speed errors inhuman tissues.4、 Investigate the degradation of the echoes in lateral and axial directions, andobtain the impact of center frequency and lateral resolution caused byultrasound degradation.5、 Present an improved synthetic aperture approach based on phase compensation. The approach corrents the phase distortion of the echoescaused by ultrasound degradation to enhace the resolution of endoscopicultrasonography.6、 Design an experiment system for synthetic aperture approach to implementboth tissue experiment and multi-point targets experiment. Finally prove theeffectiveness of the approach.