Echographie par corrélation : caractéristiques et performances

Abstract
Ultrasonic imaging using the correlation technique overcomes the problems of conventional pulse echo systems by tsansmitting a continuous coded signal. The target location is determined by cross-correlation of the emitted and the received signal. The band compression allows, by increasing SNR, the retrieval of echo signals buried in the receiver noise. Thus in medical-type echography, where the signal attenuation at fixed depth is proportional to the frequency, the SNR improvement allows the use of higher frequency signals and leads to improved resolution. We report here the results of comparative experimental studies of echo B type images as obtained by the classical pulse echo and correlation techniques. Because the optimisation of the coded signal plays a crucial role in the performance of the correlation technique we will also present a comparative study of the performances of the most common codes. In particular we shall emphasise the relative importance of the central lobe as compared to the side lobes of the correlation function, which is directly connected to the dynamic of the imaging system The respective advantages of the echo images obtained with the most promising coded signals will be discussed.