Ultrasound Imaging

Ultrasound imaging uses sound waves pitched far beyond the range of human hearing. These waves are generated by the piezoelectric effect: when an electric potential is applied to certain crystals - lead zirconate is a common example - the crystal becomes excited and vibrates, producing ultrasound. When this ultrasound is passed into the body through a homogeneous tissue, it travels unimpeded until it reaches a boundary with a different tissue or organ; part or all of the wave is then reflected back and picked up by the same crystal, which converts the returning vibration into an electrical signal. That signal, representing the reflecting interface, is displayed on a screen as a deflection from a baseline, and a moving series of such reflections builds up a real-time image of the structures being scanned. Because it uses sound rather than ionising radiation, ultrasound is considered a safe, non-invasive technique suitable for repeated use, including throughout pregnancy. Clinically, it is used to image a developing foetus at different stages of pregnancy and monitor its progress; to listen to the foe …