Viscoelastic property measurement in thin tissue constructs using ultrasound

Area of Science:

• Biomedical Engineering
• Ultrasound Technology
• Tissue Mechanics

Background:

• Accurate measurement of localized tissue displacements is crucial for understanding tissue mechanics.
• Existing ultrasound elastography methods face challenges in resolving displacements in thin tissue constructs on rigid substrates.

Purpose of the Study:

• To develop and validate a dual-element ultrasound transducer system for generating and tracking localized tissue displacements in thin tissue constructs.
• To investigate the resonant behavior of thin tissue constructs under acoustic radiation force.
• To apply advanced filtering techniques for estimating tissue mechanical properties.

Main Methods:

• A dual-element system comprising a 5-MHz acoustic radiation force (ARF) transducer and a 25-MHz imaging transducer was utilized.
• Synchronized operation with arbitrary waveform generation and data capture enabled jitter-free pulse-echo data acquisition.
• Correlation-based speckle tracking was employed to capture tissue axial deformation dynamics up to 10 kHz pulse-repetition frequency.
• A second-order forced harmonic oscillator (FHO) model and extended Kalman filter (EKF) were used for material property estimation.

Main Results:

• The system successfully generated and tracked localized tissue displacements in constructs as thin as 500 micrometers.
• Tissue-mimicking phantoms exhibited resonant behavior, with resonance frequency inversely proportional to sample thickness.
• The EKF robustly estimated the time-invariant stiffness (apparent modulus) of the samples.
• Apparent viscosity was identified as a time-varying property, consistent with FHO model predictions.

Conclusions:

• The developed dual-element ultrasound system is effective for characterizing mechanical properties of thin tissue constructs.
• The observed resonant behavior provides a basis for high-contrast imaging in elastography.
• The FHO model coupled with EKF offers a reliable method for dynamic material property estimation in biological tissues.