Contact surface and material nonlinearity modeling of human lungs

Abstract

A finite element model has been developed to investigate the effect of contact surfaces and hyperelastic material properties on the mechanical behavior of human lungs of one lung cancer patient. The three-dimensional model consists of four parts, namely the left lung, right lung, tumor in the left lung and chest wall. The interaction between the lungs and chest wall was modeled using frictionless surface-based contact. Hyperelastic material properties of the lungs are used in the model. The effect of the two parameters is investigated by tracking the tumor movement, and by comparing the analytical results to the patient bifurcation points: 45 points in each lung and 18 points around the tumor. The accuracy of the model is improved by including the contact surface and hyperelastic material properties. The average error and the standard deviation (SD) in modeling the displacement in the SI direction are reduced from 0.68 (SD = 0.34) cm in the elastic model to 0.09 (0.21) cm in the contact-hyperelastic model. Similarly, the average error (SD) of tumor location decreases from 0.71 (0.21) cm in the elastic material without contact to -0.03 (0.24) cm in the hyperelastic material with contact model.

Predictive modeling of lung motion over the entire respiratory cycle using measured pressure‐volume data, 4DCT images, and finite‐element analysis

“…We have used the P-V data to apply pressure boundary conditions to the surface of the lung model based on its instantaneous volume so that the relationship between lung volume and pressure is maintained. We believe that this is an advantage of our modeling approach compared to models that apply displacement boundary conditions 35,38 to drive lung motion. The features of our FE model are summarized in Table I.…”

“…31,32 Although deformable image registration models 33 and nonmodel heuristic approaches 25 incorporating surrogates have provided information on tumor displacement caused by respiration, advanced finite-element methods ͑FEMs͒ can address limitations associated with these methods, including prediction of localized deformation of tumor 34 and interorgan interactions such as the pleural sliding. 35 Finite-element lung models have also been used to evaluate the effect of gravity on respiratory physiology 36 and to find surface matching of organs in two images in deformable image registration techniques. [37][38][39][40] Recently, finite-element lung models for tumor tracking at the end of inhalation incorporating contact conditions have been proposed.…”

“…[37][38][39][40] Recently, finite-element lung models for tumor tracking at the end of inhalation incorporating contact conditions have been proposed. 35,34 In FEM, the effectiveness of the model and its accuracy in predicting tumor motion depend on several important issues including the quality of the patient geometric model and the regularity and accuracy of the finite-element mesh. In previous works by Brock et al, 38 Werner et al, 34 and Villard et al, 41 multistep procedures such as isosurface construction, multiple iterative mesh smoothing, relaxing, and decimation may result in undue simplification and artifacts in the modeling as pointed out in Sec.…”

“…III A of this paper. Additionally, the idea of using a projected displacement boundary condition by Brock et al 38 and Al-Mayah et al 35,42 on the surface of the lungs may misrepresent the physiology and incorrectly represent contact conditions with adjacent tissues.…”

“…None of these FEM models discussed above considered the nonlinear elastic property associated with lung motion. Recently, Al-Mayah et al 35,42 has improved the FEM-based 3D lung model in Brock et al 38 by including contact conditions and nonlinear material properties. Prescribed displacement boundary conditions, similar to that in Brock et al, 38 have been applied and the interaction between the walls of the lungs and the chest has been modeled using frictionless surface-based elements.…”