Interlaboratory comparison of backscatter coefficient estimates for tissue-mimicking phantoms

Abstract

Ultrasonic backscatter is useful for characterizing tissues and several groups have reported methods for estimating backscattering properties. Previous interlaboratory comparisons have been made to test the ability to accurately estimate the backscatter coefficient (BSC) by different laboratories around the world. Results of these comparisons showed variability in BSC estimates but were acquired only for a relatively narrow frequency range, and, most importantly, lacked reference to any independent predictions from scattering theory. The goal of this study was to compare Faran-scattering-theory predictions with cooperatively-measured backscatter coefficients for low-attenuating and tissue-like attenuating phantoms containing glass sphere scatterers of different sizes for which BSCs can independently be predicted. Ultrasonic backscatter measurementswere made for frequencies from 1 to 12 MHz. Backscatter coefficients were estimated using two different planar-reflector techniques at two laboratories for two groups of phantoms. Excellent agreement was observed between BSC estimates from both laboratories. In addition, good agreement with the predictions of Faran's theory was obtained, with average fractional (bias) errors ranging from 8-14%. This interlaboratory comparison demonstrates the ability to accurately estimate parameters derived from the BSC, including an effective scatterer size and the acoustic concentration, both of which may prove useful for diagnostic applications of ultrasound tissue characterization.

FIG. 1

Schematic of phantom shape, dimensions and construction materials.

FIG. 2

Diameter distribution for Potters 3000E spheres. These spheres were used in the F1, F2, M1, M2 and M3 TLA phantoms.

FIG. 3

Diameter distribution for Duke Scientific 41 μm spheres. These spheres were used in the 41 μm glass spheres in the agar LA phantom.

FIG. 4

Diameter distribution for Potters 3000E spheres sieved to 150 to 180 μm. These spheres were used in the 150–180 μm glass spheres in the agar LA phantom.

FIG. 5

Setup for through-transmission sound speed and attenuation measurements.

FIG. 6

Attenuation measurement comparison for the LA 41 μm glass spheres in agar (A) and TLA M2 phantom (B). Standard deviations for the WI measurements were very small (around 0.02–0.08) and are not visible on these graphs.

FIG. 7

BSC for the F1 and F2 TLA phantoms. The ka axis was determined by using the volume-weighted mean radius of the scatterers within the phantoms.

FIG. 8

BSC for the M1 TLA phantom. The ka axis was determined by using the volume-weighted mean radius of the scatterers within the phantoms.

FIG. 9

BSC for the M2 TLA phantom. The ka axis was determined by using the volume-weighted mean radius of the scatterers within the phantoms.

FIG. 10

BSC for the M3 TLA phantom. The ka axis was determined by using the volume-weighted mean radius of the scatterers within the phantoms.

FIG. 11

BSC for the A1 and A2 TLA phantoms.

FIG. 12

BSC for the 41 μm glass spheres in agar LA phantom. Single black and magenta dots represent BSC for diseased and healthy liver, respectively. The vertical green dotted bar represents the range of BSCs for infiltrating ductal carcinomas (IDC) and the vertical cyan dashed bar represents the range of BSCs for breast fat.

FIG. 13

BSC for the 150–180 μm glass spheres in agar LA phantom.