MSEE, SonoSite, Inc, 21919 30th Dr SE, Bothell, WA 98021-3904 USA.,
J Ultrasound Med. 2013 Nov;32(11):1897-911. doi: 10.7863/ultra.32.11.1897.
This article examines the challenges associated with making acoustic output measurements at high ultrasound frequencies (>20 MHz) in the context of regulatory considerations contained in the US Food and Drug Administration industry guidance document for diagnostic ultrasound devices. Error sources in the acoustic measurement, including hydrophone calibration and spatial averaging, nonlinear distortion, and mechanical alignment, are evaluated, and the limitations of currently available acoustic measurement instruments are discussed. An uncertainty analysis of acoustic intensity and power measurements is presented, and an example uncertainty calculation is done on a hypothetical 30-MHz high-frequency ultrasound system. This analysis concludes that the estimated measurement uncertainty of the acoustic intensity is +73%/-86%, and the uncertainty in the mechanical index is +37%/-43%. These values exceed the respective levels in the Food and Drug Administration guidance document of 30% and 15%, respectively, which are more representative of the measurement uncertainty associated with characterizing lower-frequency ultrasound systems. Recommendations made for minimizing the measurement uncertainty include implementing a mechanical positioning system that has sufficient repeatability and precision, reconstructing the time-pressure waveform via deconvolution using the hydrophone frequency response, and correcting for hydrophone spatial averaging.
这篇文章探讨了在美 FDA 诊断超声设备行业指南规定的监管考虑因素下，在高于 20MHz 的高频超声下进行声学输出测量所面临的挑战。评估了声学测量中的误差源，包括水听器校准和空间平均、非线性失真和机械对准，并讨论了当前可用的声学测量仪器的局限性。对声强和功率测量的不确定度进行了分析，并对一个假设的 30MHz 高频超声系统进行了不确定度计算示例。该分析得出的结论是，声强的估计测量不确定度为+73%/-86%，机械指数的不确定度为+37%/-43%。这些值超过了 FDA 指南文件中分别为 30%和 15%的相应水平，这更能代表与表征低频超声系统相关的测量不确定性。为了最小化测量不确定性而提出的建议包括：实施具有足够可重复性和精度的机械定位系统、通过使用水听器频率响应进行反卷积来重建时压波形、以及校正水听器空间平均。
