Therapy-level ultrasonic power measurement
Physiotherapy ultrasound is used in medecine to treat a large number of soft tissue injuries and involves the administration of ultrasonic power to a patient during a well defined period of time. The amount of acoustic power is indicated to a physiotherapist by a meter or calibrated dial. A properly quantified application and certain accuracy of the quantity of ultrasound energy is necssary. Several investigations carried out over the last ten years show the lack of proper calibration facilities. This project intend to address the various technical issues related to the measurement of ultrasonic power at therapeutic levels and to produce a set of deliverables which should make significant contributions to improving the quality of ultrasonic therapy equipement and ultimately to the benefit of the physiotherapy community and patient treatment.
Part funded under the EC contract SMT4-CT96-2139 (DG 12-RSMT) and administered by the Standards, Measurement and Testing Programme
Final Report 2000-06-08
A project has been completed to develop reference methods for the measurement of ultrasonic power with a validated measurement uncertainty of <7% at power levels of 1 to 20 W over the frequency range 1 to 3 MHz of collimated beams. The project is the result of collaborative research between the Physikalisch-Technische Bundesanstalt (PTB, DE), the National Physical Laboratory (NPL, UK) and the Netherlands Organisation for Applied Scientific Research, Prevention and Health (TNO-PG, NL). The work has been undertaken under the 4th Framework Programme of the EC, Contract SMT4-CT96-2139. Primary standard designs of radiation force balances based on both absorbing and reflecting targets have been constructed. Newly developed absorbing material has been investigated and is now commercially available through NPL. The methods have been validated using ultrasound transducers, which demonstrated an adequate short and long-term stability. A method to detect cavitation based on monitoring the acoustic signals produced by bubble oscillation and collapse has been established. Different procedures for obtaining degassed water have been investigated. A method showing significant promise involves the addition of sodium sulphite (Na2SO3). During the validation process, commercially-available radiation force balances and ultrasonic physiotherapy devices have also been evaluated. Limitations of current measurement methods and practices including power measurements made on transducers exhibiting a diverging beam have been identified. A correction method to correct the measurement result for diverging beams has been introduced. As a result of the project it has been shown that the three partners in the project are able to measure the ultrasonic output power of the range identified, well within the goal of the project. The maximum deviation from the grand mean of the radiation conductance G of each individual result range from 0,1% to 5,1%, depending on the transducer type. The average uncertainty of the single uncertainties of the results of the laboratories ranges from 2,6% to 3,9%. The measurement set-ups developed are now added to the standard equipment of each individual laboratory to serve the need of manufacturers in their validation processes.
Report reference: Hekkenberg, R.T., Beissner, K., Zeqiri, B., Therapy-level ultrasonic power measurement, Final Technical report SMT4-CT96-2139, European commission, BCR Information, Report EUR 19510, ISBN 92-828-9027-9, 2000