Coded excitation and nonlinear pulse compression in pulse-inversion fundamental imaging

Coded excitation can be applied in pulse-inversion-fundamental (PIF) imaging to enhance the signal-to-noise ratio with minimal destruction of the microbubbles. Nevertheless, nonlinear responses from microbubbles may cause difficulties in pulse compression and result in severe range side-lobe artifacts. The efficacy of pulse compression was evaluated by investigating several factors relevant to PIF generation using both in-vitro experiments and simulations. Results indicate that, when nonlinear responses from contrast agents are enhanced by using a higher acoustic pressure or when more microbubbles are near the resonance size of the transmit frequency, higher range side-lobes are produced after compression. On the other hand, the contrast-to-tissue ratio (CTR) in PIF imaging still increases with acoustic pressure and the nonlinear resonance of microbubbles because of elevated main-lobe level. However, the use of coded excitation is not beneficial in PIF contrast detection because the CTR after compression is consistently lower than that before compression due to obvious side-lobe artifacts.