Interlaboratory comparison of ultrasonic backscatter coefficient measurements from 2 to 9 MHz.
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.
Wear
Keith A
KA
Center for Devices and Radiological Health, Food and Drug Administration, 12720 Twinbrook Pkwy, Rockville, MD 20852, USA. kaw@cdrh.fda.gov
Stiles
Timothy A
TA
Frank
Gary R
GR
Madsen
Ernest L
EL
Cheng
Francis
F
Feleppa
Ernest J
EJ
Hall
Christopher S
CS
Kim
Beom Soo
BS
Lee
Paul
P
O'Brien
William D
WD
Oelze
Michael L
ML
Raju
Balasundar I
BI
Shung
K Kirk
KK
Wilson
Thaddeus A
TA
Yuan
Jian R
JR
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