Evaluation of therapeutic ultrasound devices: performance stability over 44 weeks of clinical use.

The aim of this study is to establish at what time intervals regular checks of therapeutic ultrasound devices (TUSD) should be made to verify power output, timer accuracy, and ultrasonic frequency. Twenty-nine TUSDs from physiotherapy departments of 11 hospitals affiliated with the University of Montreal were retained for the study. The make, model, date of purchase, and other pertinent data of the TUSDs were determined from a questionnaire completed by each participating hospital. Power output, timer accuracy, and ultrasonic frequency of the TUSDs were verified every 4 weeks during a 20-week period with 2 further verification visits at 12-week intervals to complete the study. Data collected included the duration, intensity, and frequency of use of the TUSDs. The humidity and ambient temperature of the treatment locales were also recorded. At the initial verification, 66 percent of the TUSDs were found to be outside of tolerance limits for ultrasound intensity and 35 percent had inaccurate timers. For the duration of the study (44 weeks), 62 percent (18) of the TUSDs had to be calibrated at least twice, 38 percent (11) three times, and 31 percent (9) needed to be calibrated at least four times. Statistical analysis of the data failed to identify which factor or factors caused the deterioration in calibration of these TUSDs. Among the suggestions for improving the accuracy and safety of ultrasound treatments is that calibration verification should be made every 4 weeks and at even shorter intervals for some units. The authors suggest a follow-up study to determine the results of weekly verification.