Interlaboratory comparison of backscatter coefficient estimates for tissue-mimicking phantoms

Backscatter in ultrasound is a useful property for characterizing tissues and several groups have reported methods for estimating this property. However, previous inter-laboratory comparisons of backscatter coefficient (BSC) estimates have shown variability in BSC results, were only acquired over a relatively narrow frequency range, and lacked reference to any independent predictions from scattering theory. With highly variable results and no claim of a "right" answer, our goal was to compare Faran scattering theory predictions with cooperatively measured backscatter coefficients for low- and tissue-like attenuating phantoms containing glass spheres scatterers of different sizes for frequencies from 1 to 12 MHz. Backscatter coefficients were measured using two different planar reflector techniques at two laboratories for two groups of phantoms. The use of spherical glass scatterers with well-characterized size distributions allowed calculation of the expected backscatter coefficients using Faran's theory. Results showed excellent agreement between both labs' BSC measurements and with Faran's theory. Excellent agreement with the predictions of Faran's theory demonstrates the ability to accurately estimate both effective scatterer size and acoustic concentrations, all of which may prove useful parameters for clinical diagnostic applications in tissue characterization. (Supported by NIH/NCI R01CA111289.)