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Technical Briefs

The Effect of Glisson’s Capsule on the Superficial Elasticity Measurements of the Liver

[+] Author and Article Information
Esra Roan1

Department of Biomedical Engineering, and Department of Mechanical Engineering, University of Memphis, 330 Engineering Technology Building, Memphis, TN 38152eroan@memphis.edu

1

Corresponding author.

J Biomech Eng 132(10), 104504 (Sep 28, 2010) (7 pages) doi:10.1115/1.4002369 History: Received June 30, 2009; Revised August 02, 2010; Posted August 16, 2010; Published September 28, 2010; Online September 28, 2010

In the past decade, novel tools for surgical planning and disease diagnosis have been developed to detect the liver’s mechanical properties. Some tools utilize superficial indentation type measurements to determine the elasticity of the liver parenchyma and to assume material homogeneity. In fact, the liver is a soft tissue covered with a connective sheathing that is called Glisson’s capsule. This article quantifies the effect of this capsule on the measured or “effective” elastic modulus obtained by indentation with a spherical geometry. Two sets of parametric computational studies in which the Glisson capsule thickness and elasticity were varied, demonstrated the relationship between the measured elastic response and the underlying parenchymal elastic response. Previously reported in vivo indentation data on the human liver were utilized to determine the elasticity of its parenchyma. The results indicated a linear relationship between the effective (measured) elastic response and the underlying parenchyma for the Glisson capsule thicknesses considered. When previously published human liver indentation data were analyzed, the measured elastic modulus was nearly 6.9% greater than the underlying parenchyma elastic modulus. Although the analyzed data were obtained from a single liver and yet displayed a significant variation, the Glisson capsule elasticity induced a significant but systematic error as well. The Glisson capsule thickness error was negligible for capsule parameters associated with a normal liver. Based on this work, an emphasis on the Glisson capsule’s contribution to the mechanical response of the liver would enhance the clinical potential of indentation-based novel tools for liver care.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Gross anatomy of the liver and its underlying composite structure, where the nonuniform thickness of the Glisson capsule is evident (histological image of an equine liver is obtained from R. A. Bowen at Colorado State University with permission)

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Figure 2

(a) Schematic of the FE model with boundary conditions and (b) close-up schematic showing the thin layer of Glisson’s capsule

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Figure 3

(a) Surface plot of the effective elastic modulus Eeff and modulus of the parenchyma Epa capturing the range of elastic moduli of human and bovine livers. Glisson’s capsule elastic modulus EGC is 1.1 MPa for this analysis. (b) Effective elastic modulus as a function of parenchymal elastic modulus for 70 μm and 100 μm capsule thicknesses with constant capsule elastic modulus. (c) Indentation profiles of the rigid indenter composite liver with 1 kPa (left) and 45 kPa (right) parenchyma elastic modulus with both having 1.1 MPa Glisson’s capsule elastic modulus.

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Figure 4

Comparison of the parenchyma elastic modulus to effective elastic modulus as a function of Glisson’s capsule elastic modulus (Epa=3 kPa)

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Figure 5

The adapted force-indentation curves for human liver and the theoretical fit using Hertzian contact mechanics. The three curves indicate the minimum, mean, and maximum of the measured values assuming one standard deviation. The arrow indicates the range of indentation depth that is analyzed to obtain the effective elastic modulus.

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