Variability in effective radiating area at 1 MHz affects ultrasound treatment intensity

Abstract

Background and Purpose: Previous research has indicated that not all ultrasound transducers heat at equal rates; however, the cause of this disparity is unclear. Variability in spatial average intensity (SAI) has been implicated in this disparity at 3 MHz. This variability has not been explored at 1 MHz. Methods: Sixty-six 5-cm2 ultrasound transducers were purchased from 6 different manufacturers. Transducers were calibrated and assessed for effective radiating area (ERA), total output power, and SAI using standardized measurement techniques. Results: Total output power values fell within US Food and Drug Administration guidelines, but there were large variations in ERA. The resulting SAI values showed large deviations (-43% to +61%) from the digitally displayed value. Intra-manufacturer SAI values varied up to 53%. Discussion and Conclusion: Spatial average intensity can vary largely from the values displayed on these ultrasound generators; in a calibrated cohort, this difference is primarily attributable to differences in measured ERA. Patterns of SAI variability within the manufacturer at 1 MHz do not follow previous reports of variability at 3 MHz. © 2008 American Physical Therapy Association.