Probing Tissue Viscoelasticity With STL Ultrasound Shearwave Spectroscopy Using Cole-Cole Diagrams

Area of Science:

• Biomedical Engineering
• Medical Imaging
• Rheology

Background:

• Shear wave elastography (SWE) estimates tissue mechanical stiffness by analyzing shear wave dispersion.
• Current SWE methods often use incomplete spectral information, limiting the accurate resolution of complex shear modulus (μ*(ω)).
• Viscoelastic properties of tissues are crucial for understanding their mechanical behavior.

Purpose of the Study:

• To propose and validate a novel approach using full-waveform information of shear wave spectra in SWE.
• To enhance the resolution of complex shear modulus (μ*(ω)) in viscoelastic tissues.
• To improve the accuracy of mechanical stiffness estimation in various tissue types and conditions.

Main Methods:

• Implemented a full-waveform spectral analysis technique in ultrasound shear wave elastography.
• Validated the approach on phantom models with varying concentrations of gelatin and oil.
• Applied the method to ex-vivo animal tissues (livers) and human post-delivery placenta, including tissues subjected to thermal ablation and chemical fixation.

Main Results:

• Full-waveform analysis provided more robust estimates of complex shear modulus (μ*) compared to cross-correlation methods.
• Reduced bias in stiffness estimation was observed, particularly in complex phantom and actual tissue samples.
• Stiffness measurements demonstrated sensitivity to changes induced by thermal ablation and glutaraldehyde exposure; reconstruction errors were significantly reduced using a power law model.

Conclusions:

• Incorporating full spectral information in SWE is essential for accurate mapping of viscoelastic tissue properties.
• Omitting shear wave attenuation leads to significant bias in stiffness estimation.
• The choice of rheological model and framework critically impacts the reconstruction of tissue viscoelastic response.