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.

Carotid atherosclerotic plaque characterisation by measurement of ultrasound sound speed in vitro at high frequency, 20MHz

“…The authors postulated that they would have benefited from the use of a common reference material. Wear et al (2005) observed a large range of variation, of up to two orders, in absolute magnitude of backscatter coefficient measured at the different centres.…”

“…A contemporary agar-based TMM has been designed and established as part of an International Electrotechnical Commission project (IEC 2001;Teirlinck, Bezemer, Kollmann, Lubbers, Hoskins, Fish, Fredfeldt, & Schaarschmidt 1998). This has found uses in a range of medical ultrasound research projects (Madsen et al 2005;Meagher et al 2007;Poepping et al 2002;Ramnarine, Kanber, & Panerai 2004). It has also been utilised at the Barts and the London NHS Trust to develop test objects investigating the feasibility of high frequency ultrasound transducers (Carey et al 2004) based on the fluoropolymer PVdF (polyvinylidene difluoride, also known as KYNAR®).…”

“…Two extensive inter-laboratory comparisons of acoustic parameters have been carried out for a standard, calibrated material (Madsen 1999;Wear et al 2005). Results for each ultrasonic property, propagation speed, attenuation coefficient & backscatter coefficient, were measured in ten different physics laboratories and then compared.…”

Evaluation of a Cardiac Ultrasound Segmentation Algorithm Using a Phantom

“…Ultrasonic properties of the materials are given in Table 1. The propagation speeds and attenuation coefficients were measured by the method of [15], and the backscatter coefficients by [16].…”

Cross-imaging system comparison of backscatter coefficient estimates from a tissue-mimicking material

“…[7][8][9] These studies have enabled researchers to uncover sources of errors in measurements that, once eliminated, resulted in inter-laboratory agreement among BSC estimates on identical samples. 8,9 The studies by Wear et al, 7 Anderson et al, 8 and King et al 9 focused on laboratory-based systems, measurement, and data processing techniques. However, to apply QUS in a clinical setting, it is necessary to also demonstrate system and operator independence of BSC estimates using arraybased ultrasound imaging systems.…”