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 sch eme. Linear frequency modulation fm, one form of pulse coding among ma ny others, has been used in this study. With this approach, one can ov ercome current peak intensity limitations. A theoretical framework tha t includes medium propagation effects, transducer bandwidth and diffra ction effects is presented, which could be used to examine the system point spread function under this imaging scheme. A prototype experimen tal set-up and signal processing are described and used for simple ima ging tasks in attenuating and nonattenuating media. Analysis of the ex perimental point spread functions shows that resolution similar to con ventional short pulse imaging can be achieved. However, the existence of large range side lobe levels usually associated with pulse compress ion 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 t hrough simulations. The technique has the potential for improving sign al-to-noise ratio (SNR), maximum penetration depth and resolution with out exceeding peak intensity limitations. Some possible applications a re discussed that merit further evaluation. Our work demonstrates the feasibility of this technique and presents a theoretical framework tha t can be used in future studies aimed at evaluating image quality, sys tem performance, and possible artifacts under such an imaging scheme. (C) 1995 Academic Press, Inc.