On the estimation of backscatter coefficients using single-element focused transducers

Abstract

The ultimate goal of quantitative ultrasound (QUS) imaging methods based on backscatter coefficient (BSC) estimates is to obtain system-independent structural information about samples. In the current study, three BSC estimation methods were compared and evaluated using the same backscattered pressure datasets in order to assess their consistency. BSC estimates were obtained from two phantoms with embedded glass spheres and compared to theoretical BSCs calculated using size distributions estimated using optical microscopy. Effective scatterer diameter and concentration estimates of the glass spheres were also obtained from the estimated BSCs. One estimation method needed to be compensated by more than an order of magnitude in amplitude in order to produce BSCs comparable to the other two methods. All calibration methods introduced different frequency-dependent effects, which could have noticeable effects on the bias of QUS estimates derived from experimental BSCs. Although in most cases the experimental QUS estimates obtained with all three methods were observed to differ by less than 10%, larger differences are expected depending on both the pressure focusing gain of the transducer (proportional to the ratio of the square of the aperture radius to the product of the wavelength and focal length) and ka range used in the estimation.

Imaging of follicular variant papillary thyroid carcinoma in a rodent model using spectral-based quantitative ultrasound techniques

“…Each data block was 0.5 mm by 0.5 mm with a 75% overlap in the axial and lateral directions. From each data block the BSC versus frequency curve within the -6 dB transducer bandwidth (25 to 45 MHz) was estimated by the method of Chen et al [11]. For calculation of the BSC, a reference spectrum for each depth location was acquired by measuring the signal reflected from a smooth Plexiglas plate.…”

Backscatter coefficient estimation using tapers with gaps

“…If the main lobe for the taper is in the frequency band [−ω ML , ω ML ], then using Equation (13), the SC is defined as (21) The SC value serves as a quality metric for a taper. SC values close to 1.0 indicate that the side lobe levels for the taper are low compared with the main lobe.…”

“…A BSC estimate was made for each data block normalized power spectrum using a method described previously. 20,21 QUS estimates can be obtained for each individual data block BSC, and a QUS map can be created by associating each data block with a pixel and assigning each pixel a color corresponding to the QUS estimate value. 22 …”

Estimating concentration of ultrasound contrast agents with backscatter coefficients: Experimental and theoretical aspects

“…29,36 The following expression was developed for weakly focused transducers under the firstorder Born approximation:…”

“…These parameters quantify the characteristic size and concentration of scatterers in a volume and are based upon the impedance difference between the scatterers and the surrounding medium. 29,30 The method was then repeated for the UCA Definity V R (Bristol-Myers Squibb, North Billerica, MA). From experimental measurements, BSCs over the 15 to 25 MHz range were used to estimate UCA concentration and compared with hemacytometer based UCA concentration estimates.…”