IEEE Trans Ultrason Ferroelectr Freq Control. 2018 Feb;65(2):258-268. doi: 10.1109/TUFFC.2017.2778509.
Over the last decade, a variety of noninvasive techniques have been developed to monitor therapeutic ultrasound procedures in support of safety or efficacy assessments. One class of methods employs diagnostic ultrasound arrays to sense acoustic emissions, thereby providing a means to passively detect, localize, and quantify the strength of nonlinear sources, including cavitation. Real array element diffraction patterns may differ substantially from those presumed in existing beamforming algorithms. However, diffraction compensation has received limited treatment in passive and active imaging, and measured diffraction data have yet to be used for array response correction. The objectives of this paper were to identify differences between ideal and real element diffraction patterns, and to quantify the impact of diffraction correction on cavitation mapping beamformer performance. These objectives were addressed by performing calibration measurements on a diagnostic linear array, using the results to calculate diffraction correction terms, and applying the corrections to cavitation emission data collected from soft tissue phantom experiments. Measured diffraction patterns were found to differ significantly from those of ideal element forms, particularly at higher frequencies and shorter distances from the array. Diffraction compensation of array data resulted in cavitation energy estimates elevated by as much as a factor of 5, accompanied by the elimination of a substantial bias between two established beamforming algorithms. These results illustrate the importance of using measured array responses to validate analytical field models and to minimize observation biases in imaging applications where quantitative analyses are critical for assessment of therapeutic safety and efficacy.
在过去的十年中，已经开发出各种非侵入性技术来监测治疗性超声程序，以支持安全性或疗效评估。一类方法使用诊断超声阵列来感测声发射，从而提供一种被动检测、定位和量化非线性源（包括空化）强度的方法。实际的阵列元件衍射图案可能与现有波束形成算法中假定的图案有很大的不同。然而，衍射补偿在被动和主动成像中受到的关注有限，并且测量的衍射数据尚未用于阵列响应校正。本文的目的是识别理想和实际元件衍射图案之间的差异，并量化衍射校正对空化映射波束形成器性能的影响。这些目标通过在诊断线性阵列上进行校准测量来实现，使用结果计算衍射校正项，并将校正应用于软组织体模实验中收集的空化发射数据。测量的衍射图案与理想元件形式的图案有很大差异，尤其是在较高频率和离阵列较短的距离处。对阵列数据进行衍射补偿会导致空化能量估计值升高多达 5 倍，同时消除了两种已建立的波束形成算法之间的大量偏差。这些结果说明了使用测量的阵列响应来验证分析场模型以及在成像应用中最小化观测偏差的重要性，在这些应用中，定量分析对于评估治疗安全性和疗效至关重要。
