title: Variability in effective radiating area and output power of new ultrasound transducers at 3 MHz.
abstract: BACKGROUND
  Spatial average intensity (SAI) is often used by clinicians to gauge therapeutic ultrasound dosage, yet SAI measures are not directly regulated by US Food and Drug Administration (FDA) standards. Current FDA guidelines permit a possible 50% to 150% minimum to maximum range of SAI values, potentially contributing to variability in clinical outcomes.
  
  
  OBJECTIVE
  To measure clinical values that describe ultrasound transducers and to determine the degree of intramanufacturer and intermanufacturer variability in effective radiating area, power, and SAI when the transducer is functioning at 3 MHz.
  
  
  METHODS
  A descriptive and interferential approach was taken to this quasi-experimental design.
  
  
  METHODS
  Measurement laboratory.
  
  
  METHODS
  Sixty-six 5-cm(2) ultrasound transducers were purchased from 6 different manufacturers.
  
  
  METHODS
  All transducers were calibrated and then assessed using standardized measurement techniques; SAI was normalized to account for variability in effective radiating area, resulting in an nSAI.
  
  
  METHODS
  Effective radiating area, power, and nSAI.
  
  
  RESULTS
  All manufacturers with the exception of Omnisound (P = .534) showed a difference between the reported and measured effective radiating area values (P < .001). All transducers were within FDA guidelines for power (+/-20%). Chattanooga (0.85 +/- 0.05 W/cm(2)) had a lower nSAI (P < .05) than all other manufacturers functioning at 3 MHz. Intramanufacturer variability in SAI ranged from 16% to 35%, and intermanufacturer variability ranged from 22% to 61%.
  
  
  CONCLUSIONS
  Clinicians should consider treatment values of each individual transducer, regardless of the manufacturer. In addition, clinicians should scrutinize the power calibration and recalibration record of the transducer and adjust clinical settings as needed for the desired level of heating. Our data may aid in explaining the reported heating differences among transducers from different manufacturers. Stricter FDA standards regarding effective radiating area and total power are needed, and standards regulating SAI should be established.
authors.affiliation: Quinnipiac University, Hamden, CT 06518, USA. Lenn.Johns@quinnipiac.edu
authors.forename: Lennart D
authors.initials: LD
authors.lastname: Johns
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Straub
authors.forename: Samuel M
authors.initials: SM
authors.lastname: Howard
mesh_terms: D002138:Calibration; D004867:Equipment Design; D019544:Equipment Failure Analysis; D004869:Equipment Safety; D006801:Humans; D015999:Multivariate Analysis; D012016:Reference Values; D012680:Sensitivity and Specificity; D014159:Transducers / Q000592:standards*; D014464:Ultrasonic Therapy / Q000295:instrumentation* / Q000592:standards; D014465:Ultrasonics