Physiotherapy ultrasound machines are commonplace in medicine and sports injury treatment but if patients are treated with the incorrect level of ultrasonic power it could not only be less helpful, it could lead to further injury.

Calibration is the answer and scientists at the National Physical Laboratory (NPL) say they have created technology that can greatly improve the accuracy of the calibration and therefore the quality of the treatment.

NPL has developed an acoustic absorber that can be retro-fitted into current calibration equipment to increase its accuracy. The upgrade has been successfully trialed where tests on a recently-repaired machine showed ultrasound power levels measured were up to 100 perecent higher than those indicated and would have delivered double the intended dose. Thanks to NPL’s acoustic absorber a potentially harmful machine was taken out of clinical service, avoiding future patient injury.



Physiotherapy machines produce beams of sound which can spread out quickly from the applicator, like a shower head that sprays water diagonally as well as forwards. Current methods of calibrating their output are not always accurate, with equipment surveys suggesting that up to 70 percent of the tens of thousands of physiotherapy machines in clinical use could be outside specification. However, equipment using the new acoustic absorber is able to accommodate spreading beams and provides much greater calibration accuracy.

Mark Hodnett, Senior Research Scientist at NPL, said:

“Out-of-spec physiotherapy ultrasound machines are being used everyday, with both patient and physiotherapist unaware of the risks they are taking. Take-up of NPL’s research by manufacturers and the NHS can offer a quick and simple way to improve the accuracy of machine calibration. This can help ensure that soft tissue injuries are treated correctly and without risk of further injury.”