EXPERIMENTAL POINT-SPREAD FUNCTION OF FM PULSE IMAGING SCHEME

In this paper, we have examined the possibility of incorporating pulse compression techniques into a conventional medical B-scan imaging scheme. Linear frequency modulation fm, one form of pulse coding among many others, has been used in this study. With this approach, one can overcome current peak intensity limitations. A theoretical framework that includes medium propagation effects, transducer bandwidth and diffraction effects is presented, which could be used to examine the system point spread function under this imaging scheme. A prototype experimental set-up and signal processing are described and used for simple imaging tasks in attenuating and nonattenuating media. Analysis of the experimental point spread functions shows that resolution similar to conventional short pulse imaging can be achieved. However, the existence of large range side lobe levels usually associated with pulse compression processing can degrade contrast resolution in medical ultrasound. We have considered various different factors that can affect the range side lobe levels and examined their effect either experimentally or through simulations. The technique has the potential for improving signal-to-noise ratio (SNR), maximum penetration depth and resolution without exceeding peak intensity limitations. Some possible applications are discussed that merit further evaluation. Our work demonstrates the feasibility of this technique and presents a theoretical framework that can be used in future studies aimed at evaluating image quality, system performance, and possible artifacts under such an imaging scheme. (C) 1995 Academic Press, Inc.