Shear Induced Non-Linear Elasticity Imaging: Elastography for Compound Deformations

Area of Science:

• Biomedical Engineering
• Medical Imaging
• Acoustics

Background:

• Non-linear ultrasound elastography aims to measure tissue mechanical properties under finite deformations.
• Current methods show high bias (10-50%) when deformation deviates from pure uni-axial compression.
• Clinical translation requires motion-agnostic estimators due to non-uniaxial freehand transducer motion.

Purpose of the Study:

• To derive a method for measuring the Non-Linear Shear Modulus (NLSM) under combined shear and axial deformations.
• To develop a motion-agnostic non-linearity estimator for improved clinical translation of elastography.
• To reduce bias errors in non-linear elasticity estimates for general deformation conditions.

Main Methods:

• Combined quasi-static strain imaging with Single-Track Location-Shear Wave Elastography (STL-SWEI).
• Generated local estimates of axial strain, shear strain, and Shear Wave Speed (SWS).
• Reconstructed non-linear elastograms using a novel nonlinear shear modulus estimation scheme for general deformations.

Main Results:

• Reduced bias in NLSM values to 6-13% for general deformations.
• Validated results on tissue-mimicking phantoms against mechanical measurements and multiphysics simulations.
• Demonstrated 10-15 dB SNR improvement and 25-30% CNR improvement for shear over uni-axial compression.

Conclusions:

• The derived method provides consistent non-linear elasticity estimates irrespective of applied deformation type.
• High fidelity NLSM estimates can be obtained at ~30% lower strain under shear deformation.
• The technique enhances scan safety and reduces sonographer effort, facilitating clinical translation.