Sensitivity of effective radiating area measurement for therapeutic ultrasound transducers to variations in hydrophone scanning technique.

Clinical efficacy and safety may be compromised if output from ultrasonic therapy transducers differs significantly from the indicated value. Space-averaged effective intensities selected for treatment are a ratio of the emitted ultrasonic power to the effective radiating area (ERA). In this study, ERA measurements for 17 commercially available devices were obtained by using a hydrophone scanning technique, and sources of systematic error were assessed by computer simulation. Marginal differences in technique may lead to differences of up to 50% in measured values. Suggestions are made for the improvement of consistency in such measurements.