Quantitative characterization of viscoelastic behavior in tissue-mimicking phantoms and ex vivo animal tissues.

Ashkan Maccabi,George N Saddik,Andrew Shin,Nikan K Namiri,Maie St John,Neha Bajwa,Warren Grundfest,Zachary D Taylor,Etienne Dague

doi:10.1371/journal.pone.0191919

Ashkan Maccabi, George N Saddik + Show 7 more

Open Access

https://doi.org/10.1371/journal.pone.0191919

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Abstract

Viscoelasticity of soft tissue is often related to pathology, and therefore, has become an important diagnostic indicator in the clinical assessment of suspect tissue. Surgeons, particularly within head and neck subsites, typically use palpation techniques for intra-operative tumor detection. This detection method, however, is highly subjective and often fails to detect small or deep abnormalities. Vibroacoustography (VA) and similar methods have previously been used to distinguish tissue with high-contrast, but a firm understanding of the main contrast mechanism has yet to be verified. The contributions of tissue mechanical properties in VA images have been difficult to verify given the limited literature on viscoelastic properties of various normal and diseased tissue. This paper aims to investigate viscoelasticity theory and present a detailed description of viscoelastic experimental results obtained in tissue-mimicking phantoms (TMPs) and ex vivo tissues to verify the main contrast mechanism in VA and similar imaging modalities. A spherical-tip micro-indentation technique was employed with the Hertzian model to acquire absolute, quantitative, point measurements of the elastic modulus (E), long term shear modulus (η), and time constant (τ) in homogeneous TMPs and ex vivo tissue in rat liver and porcine liver and gallbladder. Viscoelastic differences observed between porcine liver and gallbladder tissue suggest that imaging modalities which utilize the mechanical properties of tissue as a primary contrast mechanism can potentially be used to quantitatively differentiate between proximate organs in a clinical setting. These results may facilitate more accurate tissue modeling and add information not currently available to the field of systems characterization and biomedical research.

Highlights

Evaluation of viscoelastic properties of targets plays a crucial role in material science and medical diagnosis
The viscoelastic behavior of tissue-mimicking phantoms (TMPs) and ex vivo porcine and rat tissues were examined by a micro-indentation technique using a stainless steel sphere
Given that biological tissues behave as viscoelastic materials, long term shear modulus, relaxation time constant, and elasticity must be considered in their evaluation

Summary

Introduction

Evaluation of viscoelastic properties of targets plays a crucial role in material science and medical diagnosis. Tumorous tissues are typically characterized by an elastic modulus that differs from surrounding healthy tissue by several orders of magnitude [4, 5] Such tissue contrast has been leveraged to delineate tissue margins between diseased and normal regions [4, 5]. Standard clinical practice, especially in head and neck subsites, relies heavily on palpation in determining relative tissue stiffness [1, 2]. This method is based on a qualitative assessment of the region, and in many cases, the size and/or the location of the lesion makes this technique an insufficient method for medical diagnosis. A non-invasive, accurate, and high-resolution technique that uses viscoelastic properties of tissue to generate contrast may be more appropriate to detect small tissue abnormalities that are otherwise occult in palpation assessment

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