Acoustic output as measured by thermal and mechanical indices and its bio-effect during ultrasound scanning in obstetrics

Abstract

While ultrasound (US) is supposed to be totally safe, it is a form of energy. Diagnostic ultrasound (DUS) has the prospect to have effects on living tissues it crosses, such as bio-effects. The two most important mechanisms for effects are thermal and non-thermal, also called mechanical. These two main mechanisms are indicated on screen by two indices: the thermal index (TI) and the mechanical index (MI), to express the potential for rise in temperature at the ultrasound’s focal point and the probability of harm from the mechanical effects such as cavitation. It is important to understand bio-effects of acoustic output during ultrasound scanning in obstetrics. This paper identifies the need for users of ultrasound to understand thermal and mechanical indices appearing on ultra-sound screens. Some users do not use the indices and others do not know or are unaware of their importance.