Pre-enhancement of chirp signal for inverse filtering in medical ultrasound

In medical ultrasound imaging, the axial resolution is l i i t e d by the bandwidth of the transducer. The frequency response of the transducer usually peaks at its center frequency f, but falls off at higher and lower frequencies. In a linear frequency modulation (FM) pulse coding technique for imaging, the frequency can be swept across the entire bandwidth of the transducer. In this technique it is possible to apply at the input an amplitude boost function [l] that is the inverse of the transducer frequency response. Thus the output from the transducer is an equalized FM pulse, with a wider effective bandwidth. Subsequent auto correlation or pulse compression processing preserves this bandwidth and consequently improves the resolution. This concept has been evaluated experimentally in this paper.