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首页> 外文期刊>Ultrasonics, Ferroelectrics and Frequency Control, IEEE Transactions on >Phase-dependent dual-frequency contrast imaging at sub-harmonic frequency
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Phase-dependent dual-frequency contrast imaging at sub-harmonic frequency

机译：次谐波频率的相位相关双频对比成像

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摘要

Sub-harmonic imaging techniques have been shown to provide a higher contrast-to-tissue ratio (CTR) at the cost of relatively low signal intensity from ultrasound contrast agents (UCAs). In this study, we propose a method of dual-frequency excitation to further enhance the CTR of subharmonic imaging. A dual-frequency excitation pulse is an amplitude-modulated waveform which consists of two sinusoids with frequencies of f1 (e.g., 9 MHz) and f2 (e.g., 6 MHz) and the resulting envelope component at (f1 - f2) (e.g., 3 MHz) can serve as a driving force to excite the nonlinear response of UCAs. In this study, the f2, at twice of the resonance frequency of UCAs, is adopted to efficiently generate a sub-harmonic component at half of the f2 frequency, and f1 is included to enhance the high-order nonlinear response of UCAs at the sub-harmonic frequency. The second- and third-order nonlinear components resulting from the envelope component would spectrally overlap at the sub-harmonic frequency when f1 and f2 are properly selected. We further optimize the generation of the sub-harmonic component by tuning the phase terms between second- and third-order nonlinear components. The results show that, with dual-frequency excitation, the CTR at sub-harmonic frequency improves compared with the conventional tone-burst method. Moreover, the CTR changes periodically with the relative phase of the separate frequency component in the dual-frequency excitation, leading to a difference of as much as 9.1 dB between the maximal and minimal CTR at 300 kPa acoustic pressure. The echo produced from the envelope component appears to be specific for UCAs, and thus the proposed method has the potential to improve both SNR and CTR in sub-harmonic imaging. Nevertheless, the dual-frequency waveform may suffer from frequency-dependent attenuation that degrades the generation of the envelope component. The deviation of the micro-n-nbubble?????????s resonance characteristics from the selection of dual-frequency transmission may also decrease the CTR improvement.
机译：已显示亚谐波成像技术以来自超声造影剂（UCA）的相对较低的信号强度为代价提供更高的组织对比度（CTR）。在这项研究中，我们提出了一种双频激励的方法，以进一步提高次谐波成像的CTR。双频激励脉冲是一个调幅波形，由两个正弦曲线组成，频率分别为f1（例如9 MHz）和f2（例如6 MHz），频率为（f1-f2）（例如3兆赫）可以作为激发UCA非线性响应的驱动力。在这项研究中，采用f2是UCA共振频率的两倍，以有效地产生一半f2频率的次谐波分量，并且包括f1以增强UCA在次谐波的高阶非线性响应。 -谐波频率。当正确选择f1和f2时，由包络分量产生的二阶和三阶非线性分量将在次谐波频率上频谱重叠。我们通过调整二阶和三阶非线性分量之间的相位项，进一步优化了次谐波分量的生成。结果表明，在双频激励下，与传统的音爆方法相比，次谐波频率下的CTR有所提高。此外，在双频激励中，CTR随分离频率分量的相对相位而周期性变化，从而导致在300 kPa声压下最大和最小CTR之间的差异高达9.1 dB。从包络分量产生的回波似乎是UCA特有的，因此，所提出的方法具有改善次谐波成像中SNR和CTR的潜力。但是，双频波形可能会遭受与频率相关的衰减，从而使包络分量的生成变差。微n气泡的共振特性与双频传输选择的偏离也可能会降低CTR的改善。

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