1. Advantages of ultrasound for imaging

Optics, electronics and now acoustics are the three fields exploited by microscopy. The use of ultrasound in microscopy dates back to the 1970s, following in particular the work of research teams at Stanford University (California), where transducers operating in frequency ranges of several hundred megahertz were developed in the early 1960s. The first instruments were marketed in the late 1980s. Today, there are several manufacturers worldwide (see the fact sheet at the end of this article). Because of the nature of the waves used, the acoustic microscope offers the usual advantages of ultrasound: non-ionizing, low-intensity radiation (a few milliwatts to a few hundred milliwatts), which is therefore harmless for biomedical applications, and non-destructive when it comes to observing solids near their surface or at depth (observations not requiring chemical attack). The resolution of this...