Characterising ultrasonic physiotherapy systems by performance and safety now internationally agreed.

The IEC 1689 standard specifies: methods of measurement, characterisation of the output performance, requirements for safety due to the ultrasonic field generated, characteristics to be declared by manufacturers and acceptance criteria for aspects of performance. For the characterisation, reference as well as routine testing methods are described. Important parameters such as effective radiating area (AER), beam nonuniformity ratio (RBN) (characterising 'hot-spots': potentially harmful to patients) and beam type have been re-defined. The quality, reproducibility and accuracy of measurements of AER are significantly improved compared to those in IEC 150 (which is now replaced) and the FDA 1050.10 (USA) standards. As a result, values of effective intensity are shown to be significantly higher than those obtained using the FDA 1050.10 (USA) definitions. As it may be expected that the new standard will be implemented worldwide, this problem is just a matter of time. The standard discussed above specifies the need for acoustic power measurement with an accuracy of more than 15%. However, several investigations carried out over the last ten years show a lack of proper facilities to calibrate the acoustic output power at physiotherapy levels. A project to investigate the complications and to produce definitive guidance for therapy-level power measurements is funded by the EC and has been started recently. Future activities will be undertaken to estimate the expected temperature rise in tissue due to the ultrasonic field. Such a figure may result in an improved judgement of the ultrasonic safety aspects of physiotherapy systems.