Smith Stephanie F, Miloro Piero, Axell Richard, Ter Haar Gail, Lees Christoph
Department of Urology, Aintree University Hospital, UK.
Ultrasound and Underwater Acoustics, National Physical Laboratory, UK.
Ultrasound. 2021 May;29(2):73-82. doi: 10.1177/1742271X20953197. Epub 2020 Sep 14.
The quantification of heating effects during exposure to ultrasound is usually based on laboratory experiments in water and is assessed using extrapolated parameters such as the thermal index. In our study, we have measured the temperature increase directly in a simulator of the maternal-fetal environment, the 'ISUOG Phantom', using clinically relevant ultrasound scanners, transducers and exposure conditions.
The study was carried out using an instrumented phantom designed to represent the pregnant maternal abdomen and which enabled temperature recordings at positions in tissue mimics which represented the skin surface, sub-surface, amniotic fluid and fetal bone interface. We tested four different transducers on a commercial diagnostic scanner. The effects of scan duration, presence of a circulating fluid, pre-set and power were recorded.
The highest temperature increase was always at the transducer-skin interface, where temperature increases between 1.4°C and 9.5°C were observed; lower temperature rises, between 0.1°C and 1.0°C, were observed deeper in tissue and at the bone interface. Doppler modes generated the highest temperature increases. Most of the heating occurred in the first 3 minutes of exposure, with the presence of a circulating fluid having a limited effect. The power setting affected the maximum temperature increase proportionally, with peak temperature increasing from 4.3°C to 6.7°C when power was increased from 63% to 100%.
Although this phantom provides a crude mimic of the in vivo conditions, the overall results showed good repeatability and agreement with previously published experiments. All studies showed that the temperature rises observed fell within the recommendations of international regulatory bodies. However, it is important that the operator should be aware of factors affecting the temperature increase.
超声暴露期间热效应的量化通常基于在水中进行的实验室实验，并使用诸如热指数等外推参数进行评估。在我们的研究中，我们使用临床相关的超声扫描仪、换能器和暴露条件，在母胎环境模拟器“ISUOG体模”中直接测量了温度升高情况。
本研究使用了一个仪器化体模，该体模设计用于模拟孕妇腹部，并能够在代表皮肤表面、皮下、羊水和胎儿骨骼界面的组织模拟物中的位置记录温度。我们在一台商用诊断扫描仪上测试了四种不同的换能器。记录了扫描持续时间、循环流体的存在、预设和功率的影响。
温度升高最高的部位始终是换能器与皮肤的界面，在该界面观察到温度升高在1.4°C至9.5°C之间；在组织更深层和骨骼界面观察到较低的温度升高，在0.1°C至1.0°C之间。多普勒模式产生的温度升高最高。大部分加热发生在暴露的前3分钟，循环流体的存在影响有限。功率设置成比例地影响最大温度升高，当功率从63%增加到100%时，峰值温度从4.3°C增加到6.7°C。
尽管这个体模只是对体内情况的粗略模拟，但总体结果显示出良好的可重复性，并且与先前发表的实验结果一致。所有研究均表明，观察到的温度升高在国际监管机构的建议范围内。然而，操作人员应了解影响温度升高的因素，这一点很重要。
