The Research Of Digital Medical Ultrasonic Endoscope Imaging System

The ultrasonic endoscope, which combines an electronic endoscope and a miniultrasonic imaging system, sends a micro ultrasonic probe into coelom through thebiopsy channel of the electronic endoscope. In this way, the ultrasonic endoscope canget pictures of the alimentary canal mucosal surface and images of the full histologyof the digestive organs simultaneity。Endoscopic ultrasonography has been provenvery effective for diagnosing gastrointestinal diseases.According to the limitation of foreign ultrasonic endoscopes, such as Fujinon'sSP-501 UA, we propose a new design which uses a micro ultrasonic motor situated atthe tip of the endoscope to rotate the transducer. The ultrasonic motor and thetransducer compose a micro probe which enters the coelom through the biopsychannel of the electronic endoscope to get scanning images of the digestive organs. Asa result, the life-span of the ultrasonic endoscope is increased greatly.The main researches of this dissertation are shown as the following:1. According to the structure of the biopsy channel of the endoscope, a microultrasonic probe is presented which is composed of a micro ultrasonic motor and amicro transducer. The external diameter of the probe is 1.8 mm, the inflexible lengthis 14 mm and the scanning frequency is 5 frame per second. In the experiment, theprobe can revolve continually for about a month with a stable revolving speed.2. In order to increase the penetration depth and the image quality of theultrasonic endoscope, a fully digital ultrasonic imaging system is designed which ismainly composed of the following parts:a) Introduce the coded excitation technique which is widely used in radarsystem into the ultrasonic imaging system. The coded excitation techniqueuses a coded pulse to excite the transducer, making the ultrasonic pulsehaving much energy and higher SNR.b) According to the Digital Down Converter technique in software radio, adigital echo receiving system is designed which is composed of a high speedA/D circuit, a digital signal processing circuit (FPGA) and an image savingcircuit. This system places the high speed A/D circuit at the front of the receiving system, sampling the echo at the intermediate frequency. As a result, all the signal processing is implemented by digital circuits which have higher SNR and stability. Moreover, the parameter of the system can be modified with the software easily.c) In order to implement the real-time display of the ultrasonic image, a high speed data transferring circuit is designed which is based on USB2.0 interface.3. Finally, a digital ultrasonic imaging experimental system has been constructed with the designed circuits above. With the experimental system, the coded excitation of the transducer has been implemented. The echo reflected from the glass possesses the character of the Barker code and is consistent with the simulating result in MATLAB. Furthermore a clear scanning image of a glass has been obtained, which validated the performance of the system.