Microbubble response to dual frequency excitation for broadband contrast imaging

Abstract

Contrast imaging relies on pulsing schemes like pulse inversion (PI), power-modulated pulse inversion (PMPI), and power modulation (PM) to isolate certain harmonic components. These multi-pulse schemes normally employ single frequency pulses (SFP). In this work, we propose dual frequency pulses (DFP) coupled with pulsing schemes (PI, PMPI, and PM) for microbubble imaging. The proposed DFP contain an amount b 1 of a fundamental frequency f and an amount b 2 of its phase-shifted (φ) second harmonic 2f. Microbubbles were excited with a variety of DFP combinations (b 1, b 2, φ) and their nonlinear response was compared to that from conventional SFP. All pulsing schemes benefit in terms of overall signal from the use of DFP by ~4–6 dB. PI benefits the most when coupled with DFP as it extracts an additional amount of nonlinear fundamental signal (~25 dB) something not feasible with SFP. It was observed that microbubble nonlinear response changes when the relative amount of f and 2f in DFP change, allowing the design of specific pulses for different microbubbles. In conclusion, since the use of DFP with pulsing schemes extracts harmonics more efficiently than SFP it has the potential to improve contrast imaging in terms of bubble sensitivity and image resolution.