Research On High-frequency Ultrasound Endoscopic Imaging Method Based On Coded Excitation

High-frequency ultrasound endoscopic imaging is a new interventional imaging technology developed in recent years.It has the advantages of high resolution,real-time imaging,no radiation,low cost,etc.,and is an important means for early detection and minimally invasive diagnosis and treatment of major diseases such as lung cancer,gastric cancer and cardiovascular.However,in order to meet the needs of various medical diagnosis and treatment applications for high-precision images,high-frequency ultrasound endoscopic imaging adopts high-frequency ultrasound work,which brings various problems such as large signal attenuation in tissues,low echo signal-to-noise ratio,and shallow imaging depth,which greatly restrict the development and application of ultrasound endoscopic imaging technology.In view of the above problems,this paper focuses on the research of coded excitation technology,explores the technical methods for optimizing high-frequency ultrasound endoscopic imaging,and carries out the following main research work:In order to increase the detection ability of high-frequency endoscopic ultrasound,the coded excitation technology and ultrasonic endoscopic imaging are combined,and a new technology of Chirp coded excitation based on pulse compression weighting method is proposed,which realizes high-quality high-frequency ultrasound endoscopic imaging.This method not only improves the imaging depth of field,but also further improves the contradiction between the level of the decoded signal sidelobe and the width of the main lobe which is difficult to reconcile,so as to take into account the spatial resolution and imaging contrast.Aiming at the problem of high sampling rate and large data volume of highfrequency ultrasonic signals,a high-frequency ultrasound endoscopic imaging method combining Chirp coded excitation and compressed sensing is proposed,which effectively reduces the amount of imaging data and the requirements for system performance.In compressed sensing technology,signal reconstruction will produce reconstruction errors,which will cause obvious interference to image due to the poor anti-interference ability of high-frequency signals.The new method combines the advantages of Chirp coded excitation technology to effectively reduce the influence of reconstruction error.Aiming at the interference caused by the motion control and connection mechanism of mechanical rotary high-frequency ultrasonic endoscopic imaging system on the signal and image,based on coded excitation,a synthetic aperture method based on phase-corrected-and-sum and coherence factor weighting is proposed,which adaptively adjusts the phase and calculates the coherence factor,realizes the signal inphase superposition and amplitude weighting,and effectively avoids the destructive interference of non-in-phase superposition of the signal while suppressing the noise.The imaging results based on the highly integrated self-made system show that the method can improve the lateral imaging resolution,40%imaging contrast,and 2.4 mm imaging depth of field at 20 MHz operating frequency.To further improve the detection ability of high-frequency ultrasound endoscopic imaging,based on the self-made miniature forward-looking high-frequency phased array probe,a high-quality rapid imaging method using coherent diverging-wave compounding method is proposed on the basis of coded excitation.This method realizes high-precision puncture biopsy navigation technology with imaging speed up to 10 kHz and endoscopic three-dimensional imaging at 40 Hz,breaking through the physical time limitation of signal transmission and reception of traditional methods.In addition,this method also lays a good foundation for the realization of other new modal ultrasound imaging in the field of endoscopic imaging.