Measurement Accuracy
Ken Coffey · Physical Therapy · 2002
To the Editor: As an ultrasound device manufacturer, I read with great interest “A Calibration Study of Therapeutic Ultrasound Units” in the March 2002 issue of Physical Therapy. I applaud the efforts of the authors in promoting an awareness that therapeutic ultrasound devices need to be calibrated annually as per the recommendations of the Food and Drug Administration (FDA). The results of the study, however, should be taken with a grain of salt. The wattmeter used to check the calibration of the equipment is not approved by the FDA, and I contend that measuring ±20% with a meter that has an accuracy of ±10% is really not good science when FDA-approved meters with an accuracy of ±3% (eg, a device produced by Ohmic Instruments*) are available. I would encourage a new study that utilizes state-of-the-art technology to perform the measurements. I think the findings would show a strong correlation between the age of devices and their displayed intensities.