title: Interlaboratory comparison of ultrasonic backscatter coefficient measurements from 2 to 9 MHz.
abstract: OBJECTIVE
  As are the attenuation coefficient and sound speed, the backscatter coefficient is a fundamental ultrasonic property that has been used to characterize many tissues. Unfortunately, there is currently far less standardization for the ultrasonic backscatter measurement than for the other two, as evidenced by a previous American Institute of Ultrasound in Medicine (AIUM)-sponsored interlaboratory comparison of ultrasonic backscatter, attenuation, and speed measurements (J Ultrasound Med 1999; 18:615-631). To explore reasons for these disparities, the AIUM Endowment for Education and Research recently supported this second interlaboratory comparison, which extends the upper limit of the frequency range from 7 to 9 MHz.
  
  
  METHODS
  Eleven laboratories were provided with standard test objects designed and manufactured at the University of Wisconsin (Madison, WI). Each laboratory was asked to perform ultrasonic measurements of sound speed, attenuation coefficients, and backscatter coefficients. Each laboratory was blinded to the values of the ultrasonic properties of the test objects at the time the measurements were performed.
  
  
  RESULTS
  Eight of the 11 laboratories submitted results. The range of variation of absolute magnitude of backscatter coefficient measurements was about 2 orders of magnitude. If the results of 1 outlier laboratory are excluded, then the range is reduced to about 1 order of magnitude. Agreement regarding frequency dependence of backscatter was better than reported in the previous interlaboratory comparison. For example, when scatterers were small compared with the ultrasonic wavelength, experimental frequency-dependent backscatter coefficient data obtained by the participating laboratories were usually consistent with the expected Rayleigh scattering behavior (proportional to frequency to the fourth power).
  
  
  CONCLUSIONS
  Greater standardization of backscatter measurement methods is needed. Measurements of frequency dependence of backscatter are more consistent than measurements of absolute magnitude.
authors.affiliation: Center for Devices and Radiological Health, Food and Drug Administration, 12720 Twinbrook Pkwy, Rockville, MD 20852, USA. kaw@cdrh.fda.gov
authors.forename: Keith A
authors.initials: KA
authors.lastname: Wear
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Stiles
authors.forename: Gary R
authors.initials: GR
authors.lastname: Frank
authors.forename: Ernest L
authors.initials: EL
authors.lastname: Madsen
authors.forename: Francis
authors.initials: F
authors.lastname: Cheng
authors.forename: Ernest J
authors.initials: EJ
authors.lastname: Feleppa
authors.forename: Christopher S
authors.initials: CS
authors.lastname: Hall
authors.forename: Beom Soo
authors.initials: BS
authors.lastname: Kim
authors.forename: Paul
authors.initials: P
authors.lastname: Lee
authors.forename: William D
authors.initials: WD
authors.lastname: O'Brien
authors.forename: Michael L
authors.initials: ML
authors.lastname: Oelze
authors.forename: Balasundar I
authors.initials: BI
authors.lastname: Raju
authors.forename: K Kirk
authors.initials: KK
authors.lastname: Shung
authors.forename: Thaddeus A
authors.initials: TA
authors.lastname: Wilson
authors.forename: Jian R
authors.initials: JR
authors.lastname: Yuan
mesh_terms: D000433:1-Propanol; D000180:Acrylic Resins; D000362:Agar; D004867:Equipment Design; D005898:Glass; D006108:Graphite; D006801:Humans; D007753:Laboratories; D019047:Phantoms, Imaging; D010969:Plastics; D014465:Ultrasonics; D014463:Ultrasonography / Q000592:standards; D014867:Water
chemical_list: D000180:Acrylic Resins; D010969:Plastics; D014867:Water; D006108:Graphite; D000362:Agar; D000433:1-Propanol