Chirp reversal power modulation contrast imaging

Abstract

Chirp excitations are known to increase significantly the signal to noise ratio (SNR). Besides, we have shown in a previous study that chirp reversal (CR) approach improves the contrast detection through an increased contrast to tissue ratio (CTR). The aim of this study is to evaluate the combination of chirp reversal with power modulation (CRPM) for contrast agent imaging. Experiments were performed using a 128 elements PZT linear array probe centered at 4 MHz. The probe was connected to a fully programmable open scanner equipped with analog transmitters. Chirped signals and pulses were transmitted at 2.5 MHz with 55% bandwidth. A flow phantom was used in which SonoVue <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">®</sup> microbubbles at a dilution of 1/2000 was introduced. RF data were recorded and then filtered using a matched filter in order to compress the scattered signals and to recover the axial resolution when chirps were used. Traditional multi-excitations schemes such as pulse inversion (PI), power modulation (PM) and their combination PIPM were implemented using pulses and chirps with or without chirp reversal approach. The use of chirp increases significantly the SNR without degrading the CTR. Compared to other methods, the combination of CR and PM increases both the CTR and the SNR. For example, the CTR using CRPM is 25.3 dB while PM alone and CR alone provided a CTR of 18.7 dB and 21.8 dB respectively.