In Vivo Layer-Specific Mechanical Characterization of Porcine Stomach Tissue Using a Customized Ultrasound Elastography System

Abstract

This paper presents in vivo mechanical characterization of the muscularis, submucosa, and mucosa of the porcine stomach wall under large deformation loading. This is particularly important for the development of gastrointestinal pathology-specific surgical intervention techniques. The study is based on testing the cardiac and fundic glandular stomach regions using a custom-developed compression ultrasound elastography system. Particular attention has been paid to elucidate the heterogeneity and anisotropy of tissue response. A Fung hyperelastic material model has been used to model the mechanical response of each tissue layer. A univariate analysis comparing the initial shear moduli of the three layers indicates that the muscularis (5.69 ± 4.06 kPa) is the stiffest followed by the submucosa (3.04 ± 3.32 kPa) and the mucosa (0.56 ± 0.28 kPa). The muscularis is found to be strongly distinguishable from the mucosa tissue in the cardiac and fundic regions based on a multivariate discriminant analysis. The cardiac muscularis is observed to be stiffer than the fundic muscularis tissue (shear moduli of 7.96 ± 3.82 kPa versus 3.42 ± 2.96 kPa), more anisotropic (anisotropic parameter of 2.21 ± 0.77 versus 1.41 ± 0.38), and strongly distinguishable from its fundic counterpart. The results are consistent with the tissue morphology and are in accordance with our previous ex vivo tissue study. Finally, a univariate comparison of the in vivo and ex vivo initial shear moduli for each layer shows that the muscularis and submucosa tissues are softer while in vivo, but the mucosa tissue is stiffer while in vivo. The results concerning the mechanical properties highlight the inhomogeneity and anisotropy of multilayer stomach tissue.

Mechanical Perspective on Increasing Brush Cytology Yield

“…The mucosal lining of the stomach has tiny holes (∼30 μm in diameter in humans) called gastric pits, , which are assumed to be periodically distributed along the mucosal surface. In addition, it is assumed that the mucosal surface is homogeneous and isotropic, with an elastic modulus E m = 1–20 kPa and Poisson’s ratio υ = 0.4. , …”

“…In addition, it is assumed that the mucosal surface is homogeneous and isotropic, with an elastic modulus E m = 1–20 kPa and Poisson’s ratio υ = 0.4. 15 , 16 …”

“…Through DMA compression tests, the elastic modulus was determined to be E m = 2.6 ± 0.3 kPa (see Figure S2 ), in accordance with previous results. 15 , 16 Considering isotropic linear elasticity and Poisson’s ratio ν = 0.4, 16 the shear modulus is then G = E m /2(1 + ν) = 0.9 kPa. Accordingly, the developed shear stress is, for example, τ xy = 10 Pa for a shear strain of γ xy = 1.1%.…”

“…In addition, it is assumed that the mucosal surface is homogeneous and isotropic, with an elastic modulus E m = 1−20 kPa and Poisson's ratio υ = 0.4. 15,16 The average stiffness of a consolidated tumor on the mucosal surface is in the range of E t = 10−60 kPa with Poisson's ratio υ = 0.3−0.4. 17−20 The roughness of a mucosal surface can be approximated by a periodic function f(x) = h p sin 2 (πx/L), where h p is the asperity height, h p ∼ 10 μm, and L is the period, L ∼ 150 μm.…”

Estimation of Anisotropic Material Properties of Soft Tissue by MRI of Ultrasound-Induced Shear Waves

“…x 1 ¼ cos 2 h ð"slow" voxelsÞ cos 2 2h ð"fast" voxelsÞ and x 2 ¼ 0 ð"slow" voxelsÞ sin 2 2h ð"fast" voxelsÞ & & (20) Voxels classified as either slow or fast were included in the fit based on the criteria in Table 2. These values and the corresponding values of the independent variables for slow and fast voxels were used in the data sets fitted by the linear regression equation (Eq.…”