Ultrasound backscatter coefficient for fat quantification is affected by the measurement depth

Area of Science:

• Medical Imaging
• Biophysics
• Ultrasound Technology

Background:

• Ultrasound attenuation coefficient (AC) estimation is known to decrease with measurement depth.
• The behavior of backscatter coefficient (BSC) with depth in ultrasound imaging is not well understood.

Purpose of the Study:

• To investigate whether the backscatter coefficient (BSC) in liver ultrasound exhibits a similar depth-dependent behavior as the attenuation coefficient (AC).
• To identify factors influencing BSC estimation in liver ultrasound.

Main Methods:

• Retrospective analysis of ultrasound data from 104 individuals using a Sequoia US system with an ultrasound-derived fat fraction (UDFF) algorithm.
• BSC data were extracted, and fractional polynomial regression was employed to model the relationship between BSC and depth, considering covariates like age, sex, skin-to-liver distance, and liver stiffness.
• Regions of interest were positioned at varying depths (1.5 to 5 cm) below the liver capsule.

Main Results:

• The best-fitting model for BSC incorporated depth as a linear and square root factor.
• BSC demonstrated a significant decrease with increasing depth, with a reduction of -13.98 dB/cm-steradian for each logarithmic increase in depth (p=0.001).
• Skin-to-liver capsule distance and liver stiffness were identified as independent predictors of BSC.

Conclusions:

• Liver ultrasound backscatter coefficient (BSC) estimation is significantly influenced by measurement depth.
• A standardized ultrasound acquisition protocol is essential for reliable comparison of BSC results and monitoring changes over time.