Flint Katelyn, Bottenus Nick, Bradway David, McNally Patricia, Ellestad Sarah, Trahey Gregg
Department of Biomedical Engineering, Duke University, Durham, North Carolina, USA.
Department of Mechanical Engineering, University of Colorado, Boulder, Colorado, USA.
J Ultrasound Med. 2020 Dec 2. doi: 10.1002/jum.15570.
Ultrasound users are advised to observe the ALARA (as low as reasonably achievable) principle, but studies have shown that most do not monitor acoustic output metrics. We developed an adaptive ultrasound method that could suggest acoustic output levels based on real-time image quality feedback using lag-one coherence (LOC).
Lag-one coherence as a function of the mechanical index (MI) was assessed in 35 healthy volunteers in their second trimester of pregnancy. While imaging the placenta or the fetal abdomen, the system swept through 16 MI values ranging from 0.15 to 1.20. The LOC-versus-MI data were fit with a sigmoid curve, and the ALARA MI was selected as the point at which the fit reached 98% of its maximum.
In this study, the ALARA MI values were between 0.35 and 1.03, depending on the acoustic window. Compared to a default MI of 0.8, the pilot acquisitions suggested a lower ALARA MI 80% of the time. The contrast, contrast-to-noise ratio, generalized contrast-to-noise ratio, and LOC all followed sigmoidal trends with an increasing MI. The R of the fit was statistically significantly greater for LOC than the other metrics (P < .017).
These results suggest that maximum image quality can be achieved with acoustic output levels lower than the US Food and Drug Administration limits in many cases, and an automated tool could be used in real time to find the ALARA MI for specific imaging conditions. Our results support the feasibility of an automated, LOC-based implementation of the ALARA principle for obstetric ultrasound.
建议超声使用者遵循“尽可能低合理可达”（ALARA）原则，但研究表明大多数人并未监测声学输出指标。我们开发了一种自适应超声方法，该方法可基于使用滞后一阶相干性（LOC）的实时图像质量反馈来建议声学输出水平。
在35名处于妊娠中期的健康志愿者中评估作为机械指数（MI）函数的滞后一阶相干性。在对胎盘或胎儿腹部成像时，系统扫描了16个范围从0.15至1.20的MI值。将LOC与MI的数据拟合为S形曲线，并将ALARA MI选为拟合达到其最大值的98%时的点。
在本研究中，根据声学窗口的不同，ALARA MI值在0.35至1.03之间。与默认MI值0.8相比，初步采集结果显示80%的情况下ALARA MI更低。对比度、对比噪声比、广义对比噪声比和LOC均随MI增加呈S形趋势。对于LOC，拟合的R在统计学上显著大于其他指标（P < 0.017）。
这些结果表明，在许多情况下，低于美国食品药品监督管理局限制的声学输出水平即可实现最大图像质量，并且可实时使用自动化工具来找到特定成像条件下的ALARA MI。我们的结果支持了基于LOC对产科超声自动实施ALARA原则的可行性。
