Physiotherapy ultrasound machines are commonplace in medicine and sports injury treatment but limitations with current calibration equipment mean they may be producing inaccurate doses that could lead to further injury. New technology developed by scientists at the National Physical Laboratory (NPL) and tested by Lothian NHS could greatly improve the accuracy of the calibration and therefore the quality of 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 by medical physics staff in NHS Lothian, 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 NPL's 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."

Dr Steve Pye, Consultant Medical Physicist in NHS Lothian, said

"Ensuring that patients are treated with the correct level of ultrasonic power has always been a difficult problem. NPL have delivered a double-whammy by making the calibration of physiotherapy equipment both simpler and more accurate."

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Source: Joe Meaney
National Physical Laboratory