Contrast Harmonic Detection with Chirp Excitation in 3f₀ Transmit Phasing

Abstract

The method of third harmonic (3f0 transmit phasing is capable of providing effective tissue background suppression for contrast-to-tissue ratio (CTR) improvement in harmonic imaging. With the additional 3f0 transmit signal to generate both the frequency-sum and the frequency-difference components of harmonic signal, the tissue suppression is achieved when the two components are opposite in phase and mutually cancel out. One major problem in 3f0 transmit phasing is the limited signal-to-noise ratio (SNR) due to the constraint on transmit amplitude. Chirp excitation can be applied in contrast harmonic imaging to enhance the SNR with minimal destruction of the microbubbles. In this paper, the effect of chirp waveform in combination with the 3f0 transmit phasing was studied using both in-vitro experiments and simulations. Our results indicate that, though the chirp transmit pulse can increase the SNR of harmonic imaging in 3f0 transmit phasing (3 dB, p < 0.001), it suffers from degraded tissue harmonic suppression and thus provides less CTR improvement as compared to a conventional pulse. The spectral mismatch between the frequency-sum and the frequency-difference components of tissue harmonic signal is particularly evident in the off-center region of second harmonic band, leading to significant residue tissue background. Consequently, with the chirp waveform, the improvement of CTR decreases from 9.5 dB to 5.9 dB (p < 0.0006) and thus a tradeoff exists between the SNR improvement and the CTR improvement in 3f0 transmit phasing.

Generalization of Multipulse Transmission Techniques for Ultrasound Imaging

“…Therefore, this technique can be used in contrast imaging as well as in tissue-harmonic imaging. 21,22 These authors also suggested using the harmonic leakage signal to generate the second-harmonic reduction signal. 23,24 Multipulse Techniques However, in conventional harmonic imaging, the following problem is always encountered: if a short pulse, that is a broadband pulse, is transmitted, there is an inevitable spectral overlap between the fundamental and harmonic frequencies of the backscattered signals.…”

“…Therefore, this technique can be used in contrast imaging as well as in tissue-harmonic imaging. 21,22 These authors also suggested using the harmonic leakage signal to generate the second-harmonic reduction signal. 23,24…”

The response of phospholipid-encapsulated microbubbles to chirp-coded excitation: Implications for high-frequency nonlinear imaging

“…24 They reported improvements in the SNR, at the expense of a reduced agent-to-tissue contrast. It was also demonstrated that chirp-coded excitation improved the SNR of 3f 0 transmit phasing techniques; 25 however, the agent-to-tissue contrast was reduced. In another study, the contrast agent response to increasing and decreasing chirp-coded pulses was observed optically and acoustically.…”

“…Chirp-coded excitation is one such technique that has been widely investigated for contrast-enhanced ultrasound imaging. 14,[18][19][20][21][22][23][24][25][26][27] In a theoretical study, Barlow and colleagues reported an analytical solution to the Keller-Herring model, to predict the response of microbubbles to chirp-coded excitation. 18 A classical perturbative analysis was employed 28 to gain insight into the impact of excitation parameters on the nonlinear response.…”

Ultrasound contrast imaging: influence of scatterer motion in multi-pulse techniques

“…The differences between these techniques lie in how the source pre-biasing signal is designed. shen et al proposed a technique transmitting a fundamental and a phase-shifted third-harmonic wave simultaneously to cancel the second harmonic [12], [13]. The same group also used the harmonic leakage signal to produce the secondharmonic reduction signal [14], [15].…”