IEEE Trans Ultrason Ferroelectr Freq Control. 2021 May;68(5):1707-1720. doi: 10.1109/TUFFC.2021.3050120. Epub 2021 Apr 26.
The development of adaptive imaging techniques is contingent on the accurate and repeatable characterization of ultrasonic image quality. Adaptive transmit frequency selection, filtering, and frequency compounding all offer the ability to improve target conspicuity by balancing the effects of imaging resolution, the signal-to-clutter ratio, and speckle texture, but these strategies rely on the ability to capture image quality at each desired frequency. We investigate the use of broadband linear frequency-modulated transmissions, also known as chirps, to expedite the interrogation of frequency-dependent tissue spatial coherence for real-time implementations of frequency-based adaptive imaging strategies. Chirp-collected measurements of coherence are compared to those acquired by individually transmitted conventional pulses over a range of fundamental and harmonic frequencies, in order to evaluate the ability of chirps to recreate conventionally acquired coherence. Simulation and measurements in a uniform phantom free of acoustic clutter indicate that chirps replicate not only the mean coherence in a region-of-interest but also the distribution of coherence values over frequency. Results from acquisitions in porcine abdominal and human liver models show that prediction accuracy improves with chirp length. Chirps are also able to predict frequency-dependent decreases in coherence in both porcine abdominal and human liver models for fundamental and pulse inversion harmonic imaging. This work indicates that the use of chirps is a viable strategy to improve the efficiency of variable frequency coherence mapping, thus presenting an avenue for real-time implementations for frequency-based adaptive strategies.
自适应成像技术的发展取决于对超声图像质量的准确和可重复的描述。自适应发射频率选择、滤波和频率合成都提供了通过平衡成像分辨率、信号与杂波比和散斑纹理的影响来提高目标显著性的能力，但是这些策略依赖于在每个所需频率下捕获图像质量的能力。我们研究了使用宽带线性调频传输，也称为线性调频信号，来加快对频率相关组织空间相干性的询问，以便实时实现基于频率的自适应成像策略。将线性调频采集的相干性测量与在基本频率和高次谐波范围内通过单独传输的常规脉冲采集的相干性测量进行比较，以评估线性调频信号复制常规采集的相干性的能力。在没有声杂波的均匀仿体中的仿真和测量表明，线性调频信号不仅复制了感兴趣区域中的平均相干性，而且还复制了频率上的相干性值分布。在猪腹部和人肝模型中的采集结果表明，随着线性调频信号长度的增加，预测精度得到提高。线性调频信号还能够预测在猪腹部和人肝模型中基本频率和脉冲反转谐波成像中频率相关的相干性降低。这项工作表明，使用线性调频信号是提高可变频率相干性映射效率的可行策略，从而为基于频率的自适应策略的实时实现提供了途径。
