Measurement of Viscoelastic Properties of Polyacrylamide-Based Tissue-Mimicking Phantoms for Ultrasound Elastography Applications
05 Apr 2010-IEEE Transactions on Instrumentation and Measurement (IEEE)-Vol. 59, Iss: 5, pp 1224-1232
TL;DR: Polyacrylamide gel based tissue-mimicking phantoms have been developed to experimentally study the role of viscoelastic properties inPhantoms and indicate that stiffer samples exhibit large variations in the storage modulus when the precompression levels are altered.
Abstract: Many ailments and/or malfunctions of the body have been observed to change the viscous behavior and elastic properties of biological soft tissues. The technique of elastography has evolved to image such properties. The clinical evidence gathered during studies involving elastography to identify cancerous lesions is very promising. However, the quantification of the resolution and specificity of elastography is best achieved under a controlled study using tissue-mimicking phantoms. One challenge is to reproduce viscoelastic behavior in phantoms as observed in biological tissues. In this paper, polyacrylamide gel based tissue-mimicking phantoms have been developed to experimentally study the role of viscoelastic properties in a controlled manner. To measure the Young's modulus, the phantoms were subjected to linear loading, and the stress-strain relationship is deduced therefrom. It is seen that the phantoms show hysteresis behavior. The viscoelastic properties of these phantoms were measured by subjecting the samples to cyclic loading. Normal forces during this process of loading were also measured as a measure of sample elasticity. To emulate the normal and pathological lesions, samples were prepared with varying concentration of monomer and studied. Three models, namely, Maxwell, Kelvin-Voigt (KV), and Kelvin-Voigt fractional derivative (KVFD), were chosen to fit the experimental data. Of these, the KVFD model was found to be best fitting for the experimental data obtained. Results indicate that stiffer samples exhibit large variations in the storage modulus when the precompression levels are altered.
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TL;DR: In this article , the acoustic and viscoelastic properties of polyvinyl alcohol (PVA) phantoms and PVA mixed with glycerol at varying concentrations were investigated.
Abstract: Ultrasound phantoms mimic the acoustic and mechanical properties of native tissues. Polyvinyl alcohol (PVA) phantoms are used extensively as models for validating ultrasound elastography approaches. However, the viscous properties of PVA phantoms have not been investigated adequately. Glycerol is a viscous liquid that has been reported to increase the speed of sound of phantoms. This study aims to assess the acoustic and viscoelastic properties of PVA phantoms and PVA mixed with glycerol at varying concentrations. The phantoms were fabricated with 10% w/v PVA in water with varying concentrations of glycerol (10%, 15% and 20% v/v) and 2% w/v silicon carbide particles as acoustic scatterers. The phantoms were subjected to either one, two, or three 24-h freeze-thaw cycles. The longitudinal sound speeds of all PVA phantoms were measured, and ranged from 1529 to 1660 m/s. Attenuation spectroscopy was performed in the range of 5 to 20 MHz. The measured attenuation followed a power-law relationship with frequency, wherein the power-law fit constants and exponents ranged from 0.02 to 0.1 dB/cm/MHzn and from 1.6 to 1.9, respectively. These results were in agreement with previous reports for soft tissues. Viscoelasticity of PVA phantoms was assessed using rheometry. The estimated values of shear modulus and viscosity using the Kelvin-Voigt and Kelvin-Voigt fractional derivative models were within the range of previously-reported tissue-mimicking phantoms and soft tissues. The number of freeze-thaw cycles were shown to alter the viscosity of PVA phantoms, even in the absence of glycerol. Scanning electron microscopy images of PVA phantoms without glycerol showed a porous hydrogel network, in contrast to those of PVA-glycerol phantoms with non-porous structure. Phantoms fabricated in this study possess tunable acoustic and viscoelastic properties within the range reported for healthy and diseased soft tissues. This study demonstrates that PVA phantoms can be manufactured with glycerol for applications in ultrasound elastography.
1 citations
TL;DR: In this paper, a uniform theoretical framework for ramp-hold-oscillation-relaxation/creep indentation tests is established and Kelvin-Voigt fractional derivative (KVFD) solutions are presented to predict the viscoelastic behavior for both quasi-static loadings (creep, relaxation) and dynamic loadings(sinusoidal displacement/force cycles at 5,10,15,20,30)Hz).
1 citations
TL;DR: In this article , a finite strain viscoelastic constitute model is proposed to describe the mechanical response of the breast tissue phantoms and the model is calibrated using experimental data for phantom tissue specimens.
Abstract: In the context of breast cancer detection, mechanical imaging is an emerging technique for screening breast cancer. In view of its promise, it deserves a detailed investigation. Development of material that can emulate tissue behavior is essential for research. This work is concerned with the fabrication of polymeric specimens to capture the mechanical behavior of human breast tissues. Three types of tissue phantoms are fabricated: fat, glandular and ductal carcinoma tissues. The fabricated phantoms are compared to available human breast tissue data obtained through compression tests and stress relaxation tests. Further, the fabricated tissue phantoms are subjected to stress relaxation tests to characterize their viscoelastic response. A finite strain viscoelastic constitute model is proposed to describe the mechanical response of the breast tissue phantoms. The model is calibrated using experimental data for phantom tissue specimens. Both phantom tissue specimens and model predictions show reasonable trends. The phantom tissues and model may be of utility in developing mechanical imaging setups.
TL;DR: In this paper , the effect of gelatin concentrations and US frequency, duty cycle, and applied voltage on the acoustic intensity and focal region of the US waves was studied using high-resolution acoustic mapping.
Abstract: Background Utilizing spatially and temporally uniform tissue-mimicking phantoms for ultrasonic applications can facilitate the characterization of beam distortion and attenuation. The implementation of acoustic phantoms can enhance the efficacy of ultrasound therapy or imaging by providing guidance on optimal ultrasonic parameters, such as frequency and power. The efficacy of phantoms is heavily dependent on the accuracy and reliability of measurement techniques employed for assessing their acoustic properties. Purpose The work aims to develop, build, and characterize, via high resolution acoustic mapping, Gelatin-Based ultrasound (US) soft tissue phantoms. To that effect, we built acoustic maps of the intensity distribution of US waves passing through the phantoms and studied the effect of gelatin concentrations and US frequency, duty cycle, and applied voltage on the acoustic intensity and focal region of the US waves. The methodology developed here offers well characterized and reproducible Gelatin-Based US phantoms for soft tissue (both acoustically and mechanically). Methods We developed gelatin-based phantoms, with conveniently adjustable parameters and measured, with high resolution, the acoustic attenuation of ultrasound waves when encountering the gelatin phantoms. This was done via a motorized acoustic system built for 3D-acoustic mapping of ultrasound waves. Mechanical assessment of the phantoms’ elasticity was carried out through unconfined compression tests. We characterized tissue mimicking phantoms with realistic acoustic properties and mechanical elasticity, emphasizing the effect of varying gelatin concentration on the ultrasound maximal intensity, thus causing acoustic attenuation throughout the acoustic profile. For validation, we used computational simulations to compare our data to predicted acoustical outcomes. Results Our results show high-resolution mapping of US waves in fluid with and without Gelatin-Based phantoms. We also confirm the impact of recipe and gelatin concentration on mechanical and acoustic characterization of phantoms. The density of the gelatin-based phantoms scales with the Young’s modulus. When characterizing the acoustic profiles of the different ultrasound transducers, the focal areas increased systematically as a function of increasing applied voltage and duty cycle yet decreased as a function of increased ultrasonic frequency. Conclusions We developed a Gelatin-Based US phantoms are a reliable and reproduce tool for examining the acoustic attenuations taking place as a function of increased tissue elasticity and stiffness. High resolution acoustic maps of the intensity distribution of US can provide essential information on the spatial changes in US wave intensity and focal point enabling a more in-depth examination of the effect of tissue on US waves.
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"Measurement of Viscoelastic Propert..." refers methods in this paper
...The measurements of these properties were done using external quasi-static [11] or dynamic [17] excitations or using ultrasound-generated radiation force [18], [19]....
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...Ultrasound elastography is a method to identify pathological changes by measuring elastic properties of tissues [11], [16] using ultrasound....
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...As opposed to a procedure involving human intervention, there are several techniques that use phase-sensitive imaging modalities such as ultrasound [11]–[13] and magnetic resonance imaging [14], [15] to image the mechanical properties of soft tissues....
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TL;DR: A balanced mechanics-materials approach and coverage of the latest developments in biomaterials and electronic materials, the new edition of this popular text is the most thorough and modern book available for upper-level undergraduate courses on the mechanical behavior of materials as discussed by the authors.
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