Charach Ron, Abramowicz Jacques, Shoham-Vardi Itana, Sheiner Eyal
Department of Obstetric and Genecology, Faculty of Health Sciences, Soroka University Medical Center, Ben-Gurion University of the Negev.
Harefuah. 2011 Jul;150(7):588-92, 617, 616.
As a form of energy, diagnostic ultrasound (DUS) has the potential to have effects on Living tissues, e.g. bioeffects. The two most likely mechanisms for bioeffects are heating and cavitation. Hyperthermia is considered teratogenic in human fetuses during the first trimester Actual temperature changes cannot be studied in the human fetus. The thermal index [TI) expresses the potential for rise in temperature at the ultrasound's focal point. The mechanical index (MI) indicates the potential for the ultrasound to induce inertial cavitation in tissues. Nevertheless, cavitation has not been documented in mammalian fetuses, since there is not an air-water interface, which is needed for the cavitation mechanism. Since an output of TI over 1.5 is a known hazard, the question is: What are the settings in which such hazardous exposure occurs? Our conclusions regarding safety of DUS, based on the data that has been available till now, are the following: (1) Ultrasound end-users are poorly informed regarding safety issues during pregnancy. Further efforts in the realm of education and training are needed in order to improve knowledge of end-users about the acoustic output of the machines and safety issues. (2) First trimester ultrasound is associated with negligible rise in the thermal index. (3) Increased acoustic output Levels, as expressed by TI levels, are reached while performing obstetrical Doppler studies. In particular, TI Levels may reach 1.5 and above. Doppler procedures should be performed with caution and should be as brief as possible during obstetrical ultrasound. (4) Acoustic exposure levels during 3D/4D ultrasound examination, as expressed by TI are comparable to the two-dimensional B-mode ultrasound.
作为一种能量形式，诊断超声（DUS）有可能对活体组织产生影响，例如生物效应。生物效应最可能的两种机制是热效应和空化效应。在孕早期，高温被认为对人类胎儿有致畸性。无法在人类胎儿身上研究实际的温度变化。热指数（TI）表示超声焦点处温度升高的可能性。机械指数（MI）表明超声在组织中诱发惯性空化的可能性。然而，在哺乳动物胎儿中尚未记录到空化现象，因为空化机制需要气 - 水界面，而胎儿体内不存在这种界面。由于TI超过1.5的输出是已知的危害，问题是：在哪些设置下会发生这种有害暴露？基于目前已有的数据，我们关于DUS安全性的结论如下：（1）超声终端用户对孕期安全问题了解甚少。需要在教育和培训领域进一步努力，以提高终端用户对设备声学输出和安全问题的认识。（2）孕早期超声检查时热指数的升高可忽略不计。（3）在进行产科多普勒检查时，TI水平所表示的声学输出水平会升高。特别是，TI水平可能达到1.5及以上。在产科超声检查中，应谨慎进行多普勒检查，并且检查时间应尽可能短。（4）三维/四维超声检查期间的声学暴露水平（以TI表示）与二维B型超声相当。
