The performance of ultrasound physiotherapy machines in Lothian Region, Scotland, 1992.

Eighty-five ultrasound therapy machines in use in Lothian Region, Scotland were tested for performance and their recalibration was expedited where necessary. The performance characteristics reported are the temporal average acoustic output power, the treatment frequency, pulse timing and treatment timer accuracy. Consideration is also given to the performance of the wide dynamic range radiation force balance that was used to make acoustic power measurements. Of the machines tested, 69% had power outputs that differed by more than 30% from the expected values. The results of power measurements are analysed according to continuous and pulsed output, single and dual frequency treatment heads and year of manufacture. Therapy machines more than 10-12 years old and modern dual frequency treatment heads performed particularly badly. This study suggests that the performance of ultrasound therapy machines has improved little in the last 20 years despite the introduction of IEC 601-2-5 in 1984.