Calvert J, Duck F, Clift S, Azaime H
Medical Physics Department, Royal United Hospital, Bath, UK.
Ultrasound Obstet Gynecol. 2007 Apr;29(4):427-32. doi: 10.1002/uog.3973.
This safety study was designed to investigate tissue heating close to the surface of transvaginal ultrasound transducers, with the objective of assessing the validity of manufacturing safety standards set by the International Electrotechnical Commission (IEC).
The transducers investigated in this study were held in contact with a layered soft-tissue mimicking material (TMM), and the temperature increase was measured at various depths using a miniature thermocouple. The temperature rise at 200 s was recorded, and the measured profiles of temperature rise with depth were compared with profiles predicted from both analytical and numeric models. Two transvaginal transducers of different manufacturers were investigated, operating in B-mode imaging, color-flow imaging and pulsed Doppler modes, using scanner settings giving acoustic output power towards the upper end of that available.
The greatest heating always occurred at the interface between the transducer and the TMM, and it reduced to about 0.1 times the surface temperature rise at a depth of 1 cm. A local maximum was observed in pulsed Doppler mode. A three-dimensional finite-element model which accounted for transducer dimensions gave a better prediction of temperature increase than a simple analytical model. The temperature profiles were compared with the depth of fetal tissue measured from a small survey of clinical scans.
It is provisionally concluded that the transducer surface temperature rise of 6 degrees C allowed to manufacturers by the IEC may give rise to an associated worst-case contribution to temperature rise due to the transducer, in fetal tissue, of between 0.5 and 1 degrees C at 1-cm depth. The contribution to tissue heating at 2 cm and deeper is negligible. Published by John Wiley & Sons, Ltd.
本安全性研究旨在调查经阴道超声换能器表面附近的组织加热情况，以评估国际电工委员会（IEC）制定的制造安全标准的有效性。
本研究中所调查的换能器与一种分层的软组织模拟材料（TMM）接触，使用微型热电偶在不同深度测量温度升高情况。记录200秒时的温度升高值，并将测量得到的温度随深度升高的曲线与分析模型和数值模型预测的曲线进行比较。研究了两个不同制造商的经阴道换能器，它们在B模式成像、彩色血流成像和脉冲多普勒模式下运行，使用的扫描设置使声输出功率接近可用功率的上限。
最大加热总是发生在换能器与TMM的界面处，在1厘米深度处降至表面温度升高值的约0.1倍。在脉冲多普勒模式下观察到一个局部最大值。考虑换能器尺寸的三维有限元模型比简单的分析模型能更好地预测温度升高情况。将温度曲线与通过对临床扫描的小型调查测量得到的胎儿组织深度进行了比较。
初步得出结论，IEC允许制造商的换能器表面温度升高6摄氏度，在胎儿组织中，在1厘米深度处可能会导致换能器引起的温度升高产生0.5至1摄氏度的相关最坏情况贡献。在2厘米及更深深度对组织加热的贡献可忽略不计。由约翰·威利父子有限公司出版。
