Ultrasonic backscatter coefficients for weakly scattering, agar spheres in agar phantoms

Abstract

Applicability of ultrasound phantoms to biological tissue has been limited because most phantoms have generally used strong scatterers. The objective was to develop very weakly scattering phantoms, whose acoustic scattering properties are likely closer to those of tissues and then compare theoretical simulations and experimental backscatter coefficient (BSC) results. The phantoms consisted of agar spheres of various diameters (nominally between 90 and 212 microm), containing ultrafiltered milk, suspended in an agar background. BSC estimates were performed at two institutions over the frequency range 1-13 MHz, and compared to three models. Excellent agreement was shown between the two laboratory results as well as with the three models.

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

“…The mean values of B Faran varied from À0.42 to 0.86 dB, which, interestingly, were better than or at least comparable to the results reported in the previous interlaboratory studies. [7][8][9] The variances of B Faran also varied among systems, and the one-standard deviation values of B Faran from all systems were within 1.3 dB. Considering both bias and variance, the BSC estimates from all the imaging systems were within about 1.5 dB from the predicted values.…”

“…One of the reasons why the BSC estimates for this sample exhibited higher accuracy (including laboratory result) than those for samples utilized in previous inter-laboratory studies [7][8][9] could be its narrow scatterer size distribution (41 6 2 lm). The narrow size range reduces the uncertainty of the theoretical predictions (for a given number of bead sizes measured to characterize the distribution) to which the measured BSCs were compared.…”

“…[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.…”

“…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. Normalizing data using echo signals from planar reflectors, as performed in the preceding studies, [7][8][9] is complicated in clinical machines because of dynamic focusing of the received beam and use of internal TGC. These systems generally exhibit greater variability in transducer geometry and beamforming functions than simple, single-element transducer systems, and this makes calculation of pulse-echo beam properties as used for BSC data reduction more challenging.…”

Experimental assessment of four ultrasound scattering models for characterizing concentrated tissue-mimicking phantoms

“…The smallest weakly scattering fluid microspheres found in the literature were around 90 -212 µm in size. 30 This means that only large scale experiments (using low frequencies) can be performed with these weakly scattering fluid microspheres.…”