Quantifying viscoelasticity of gelatin phantoms by measuring impulse response using compact optical sensors [Correspondence]

Abstract

Tissue elastography measures tissue mechanical properties, which contain important physiological information and help medical diagnosis. Instead of tracking shear wave propagation inside tissue as do magnetic resonance elastography and ultrasound based techniques, this study focuses on monitoring the propagation of surface Raleigh waves stimulated by short impulses. The method is noncontact, noninvasive, and low cost and has a potential for clinical applications. A customized device designed to measure surface wave propagation is constructed based on a laser displacement sensor (LDS). Experiments are carried out on two porcine skin gelatin phantoms of different concentrations. For each phantom, the phase velocities of specific frequencies are extracted using a cross-spectrum method and then the material elasticity and viscosity are found by fitting the phase velocities with the Voigt's model. The results suggest that measuring viscoelasticity by monitoring the response to a surface impulse is an efficient method because of the richness of frequency content of impulse responses. The results are validated with a standard continuous wave (CW) method.

Determining elastic properties of skin by measuring surface waves from an impulse mechanical stimulus using phase-sensitive optical coherence tomography

“…The Young moduli presented in table 2 are estimates obtained from averaged phase-velocity values, using values for the Poisson ratio and density that were found in the literature. However, the standard deviations of the phase velocities were less than 1 m s 21 and of the Young modulus were less than 2.5 kPa, which is small compared with the expected stiffness changes that are found in skin diseases, e.g. basal cell carcinoma tumours are 3 -50% stiffer compared with healthy skin [4,16,41].…”

“…This wave is rich in frequency content, which enables the determination of the mechanical properties of different skin layers within a single measurement and analysis. Previous studies [21,22] have suggested that measuring surface waves with both a laser displacement sensor and low-coherence interferometry is highly sensitive to the shape of the tissue surface. Therefore, it has been difficult to determine the skin properties because the skin is rough, and has curvatures [21].…”

“…Previous studies [21,22] have suggested that measuring surface waves with both a laser displacement sensor and low-coherence interferometry is highly sensitive to the shape of the tissue surface. Therefore, it has been difficult to determine the skin properties because the skin is rough, and has curvatures [21]. Also, it is difficult to obtain a detecting position containing a high signal-to-noise ratio (SNR).…”

Quantitative assessment of scleroderma by surface wave technique

“…We have verified our surface wave method by different techniques, for example, an ultrasound and laser vibrometer technique [25], a laser displacement sensor method [34], and comparison of ultrasound technique and indentation technique [35]. The repeatability of our measurements on human skin is tested by repeating five measurements at the same site on the forearm of a healthy volunteer.…”

Estimating material viscoelastic properties based on surface wave measurements: A comparison of techniques and modeling assumptions

“…Another approach taken by others has been to directly estimate the frequency-dependent surface (Rayleigh) wave speed from experimental data and then to optimize the coefficients in an assumed viscoelastic model type to minimize the difference between the measured and predicted values of wave speed. 3,[20][21][22] In an analogous manner, shear wave speed dispersion derived from elastography techniques has been used to estimate the shear viscoelasticity with an assumed viscoelastic model type. [23][24][25][26][27][28][29] In the present article, the relative merits of these approaches are explored theoretically, computationally, and experimentally.…”