Ultrasonic backscatter coefficient estimation in nonlinear regime using an in situ calibration target

Area of Science:

• Ultrasound physics
• Biomedical acoustics
• Medical imaging

Background:

• Tissue characterization using backscatter coefficient (BSC) is crucial for medical diagnostics.
• Acoustic nonlinearity can degrade BSC accuracy, particularly when using external reference spectra.
• Current reference phantom methods show increased degradation in nonlinear regimes.

Purpose of the Study:

• To investigate an in situ calibration approach for improving BSC estimates in the nonlinear acoustic regime.
• To compare the efficacy of in situ calibration against the conventional reference phantom method.

Main Methods:

• Simulations and experimental validations were conducted using phantoms and in vivo models.
• A 2 mm titanium bead served as the in situ calibration target within the interrogated medium.
• Radiofrequency data were acquired using an L9-4/38 probe (4.5–7.4 MHz bandwidth) at varying acoustic power levels.

Main Results:

• The in situ calibration approach demonstrated better agreement between low-power and high-power BSC estimates compared to the reference phantom method.
• Nonlinear effects were effectively captured by the in situ reference signal, leading to more robust BSC measurements.
• Experiments confirmed improved accuracy of BSC estimates under nonlinear conditions with in situ calibration.

Conclusions:

• In situ calibration is a superior method for accurate BSC estimation in the presence of acoustic nonlinearity.
• This technique mitigates degradation issues associated with traditional reference phantom approaches.
• The findings support the clinical utility of in situ calibration for enhanced ultrasound tissue characterization.