Assessing the benefits of using plane wave compounding when estimating backscatter coefficients with an in situ bead as a calibration target

Quantitative ultrasound (QUS) techniques provide tissue characterization and have applications in precision diagnostics and therapy monitoring. A common QUS approach estimates backscatter coefficients (BSCs) using the external reference phantom method, which does not adequately address attenuation and transmission losses. To address this issue, we previously utilized a 2 mm titanium bead as an in situ calibration reference with conventional focused wave (FW) imaging. Plane wave compounding (PWC), which transmits multiple angled plane waves, enables rapid image acquisition while maintaining quality, making it widely useful in Doppler and elastographic imaging. However, its role in BSC estimation with an in situ bead had not been investigated. We hypothesized that PWC would outperform FW, as diffraction effects vary more slowly away from the bead depth when using PWC. We tested this hypothesis by comparing BSC estimation in phantoms and in vivo rabbit mammary tumors. Results indicated that PWC with in situ calibration better compensated for attenuation loss and reduced variability in scatterer property estimates compared to FW. Specifically, the scatterer diameter variance was 15.2 μm2 when using PWC versus 45.4 μm2 when using FW where the focus was offset from the bead depth. These findings demonstrate the superiority of using PWC with an in situ calibration target for accurate, efficient BSC estimation.