Medical ultrasonics

The propagation speed of ultrasound in biological soft tissues is about 1500 ms¿11, and the attenuation rate is about 1 dBcm¿1 MHz¿1. Using piezoelectric ceramic transducers, pulse-echo techniques are widely used in diagnosis, particularly with time/position and real-time two-dimensional displays in obstetrical, abdominal and cardiological investigations. Doppler techniques are used for fetal heart motion detection and for blood-flow studies. In duplex scanning, real-time imaging is used to guide the positioning of the pulsed Doppler sample volume. Orthogonal transmission imaging, ultrasonic computed tomography and acoustic microscopy are being developed. Speckle, tissue characterisation and image-processing techniques are being investigated. The ultrasonic exposures used in diagnosis appear to be safe. Ultrasonic physiotherapy exploits beneficial biological effects, and destructive effects form the basis of the application of low- and high-frequency techniques in surgery.