title: Variability in effective radiating area at 1 MHz affects ultrasound treatment intensity.
abstract: OBJECTIVE
  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-cm(2) 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%.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Physical Therapy, Quinnipiac University, 275 Mt Carmel Ave FOTRN, Hamden, CT 06489, USA. stephen.straub@quinnipiac.edu
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Straub
authors.forename: Lennart D
authors.initials: LD
authors.lastname: Johns
authors.forename: Samuel M
authors.initials: SM
authors.lastname: Howard
mesh_terms: D002138:Calibration; D019544:Equipment Failure Analysis; D006358:Hot Temperature; D006801:Humans; D014159:Transducers; D014464:Ultrasonic Therapy / Q000295:instrumentation*; D014465:Ultrasonics