Evaluating the effect of transmit sequence on the variance of quantitative ultrasound parameter estimates

Quantitative ultrasound (QUS) parameters such as effective scatterer diameter (ESD) and effective acoustic concentration (EAC) are increasingly used to assess tissue microstructure in a system-independent manner. However, their consistency may vary with transmit wave sequences, especially in portable ultrasound systems with reduced power and acquisition constraints. This study evaluates QUS parameter consistency using a portable ultrasound system from Vermon including a 128-element, 6 MHz linear array transducer. RF data were acquired from a sample phantom containing 60-µm borosilicate glass spheres using three transmit sequences: plane wave (PW), focused wave (FW), and synthetic aperture (SA). A reference phantom containing 18-µm scatterers was used to compute the backscatter coefficients (BSC) of the sample phantom via the reference phantom method correcting for system-dependent effects. Two BSC-based parameters, effective scatterer diameter (ESD) and effective acoustic concentration (EAC), were computed by fitting the BSC to a Gaussian form factor model. These values and their coefficient of variation (CV) were computed across 30 mm × 20 mm region using sliding sub-ROIs measuring 10 wavelengths (λ) axially and 30λ laterally. SA sequence produced the most consistent ESD (CVESD = 5.2%) and EAC (CVEAC = 2.4%) estimates, compared to PW (CVESD = 8.5%, CVEAC = 2.6%) and FW (CVESD = 11.4%, CVEAC = 2.6) sequences. These findings suggest SA imaging may offer more reliable QUS parameter estimates for portable ultrasound applications.