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目的超声剪切波弹性成像临床应用前景广阔,其中剪切波传播速度检测是其技术的核心步骤。针对在小焦距下传统基于静态孔径聚焦超声发射方式的剪切波传播速度检测准确度低的问题,本文提出一种基于动态孔径控制的剪切波传播速度检测方法。方法对不同的焦距以控制活跃阵元数目的方式动态控制孔径大小;采用峰值时间法结合最小二乘法计算剪切波传播速度;利用超声仿真平台FieldⅡ,采用控制变量法对多个小焦距下的声辐射力场、标记点“位移-时间”曲线及剪切波传播速度进行了仿真研究。结果本方法可有效抑制栅瓣的出现,能获取呈现出明显主峰的走势良好的标记点“位移-时间”曲线。剪切波传播速度检测结果与理论值的相对误差更低,例如在焦距为7 mm时,与理论值相对误差降低了16.585%;在焦距为9 mm时,降低了15.205%。结论基于动态孔径控制的剪切波传播速度检测方法能合理控制小焦距下的声辐射力,提升剪切波传播速度检测准确度,为超声剪切波弹性成像技术的进一步发展提供理论依据。
Objective The clinical application of ultrasonic shear wave elastography has broad prospects. Among them, the detection of shear wave propagation velocity is the core step of its technique. Aiming at the problem of low accuracy of shear wave propagation velocity detection based on static aperture focused ultrasonic emission with small focal length, this paper presents a shear wave propagation velocity detection method based on dynamic aperture control. The method controls the aperture size dynamically for different focal lengths by controlling the number of active elements. The propagation velocity of shear wave is calculated by the peak time method combined with the least squares method. Using the field simulation platform of Field II, Acoustic radiation force field, marked point “displacement - time ” curve and shear wave propagation speed were simulated. Results The proposed method can effectively suppress the appearance of grating lobe and obtain the trend of marked “displacement - time” curve with obvious main peak. The relative error between the shear wave propagation velocity and the theoretical value is lower. For example, the relative error with the theoretical value is reduced by 16.585% when the focal length is 7 mm and 15.205% when the focal length is 9 mm. Conclusion The shear wave propagation velocity detection method based on dynamic aperture control can rationally control the acoustic radiation force under small focal length and improve the detection accuracy of shear wave propagation velocity, which provides a theoretical basis for the further development of ultrasonic shear wave elastography.