Deformable image registration of heterogeneous human lung incorporating the bronchial tree

Abstract

Purpose:To investigate the effect of the bronchial tree on the accuracy of biomechanical-based deformable image registration of human lungs. Methods: Three dimensional finite element models have been developed using four dimensional computed tomography image data of ten lung cancer patients. Each model is built of a body, left and right lungs, tumor, and bronchial trees. Triangular shell elements are used for the bronchial trees while tetrahedral elements are used for other components. Hyperelastic material properties based on experimental investigation on human lungs are used for the lung parenchyma. Different material properties are assigned for the bronchial tree using five values for the modulus of elasticity of 0.01, 0.12, 0.5, 10, and 18 MPa. Lungs are modeled to slide inside chest cavities by applying frictionless contact surfaces between each lung and corresponding chest cavity. The accuracy of the models is examined using an average of 40 bronchial bifurcation points identified on inhale and exhale images. Relative accuracy is evaluated by comparing the displacement of all nodes within the lungs as well as the dosimetric difference at the exhale position predicted by the model. Results: There is no significant effect of bronchial tree on the model accuracy based on the bifurcation points analysis. However, on the local level, using an average of 38 000 nodes, there is a maximum difference of 8.5 mm in the deformation of the bronchial trees, as the modulus of elasticity of the bronchial trees increases from 0.01 to 18 MPa; however, more than 96% of nodes are within a 2.5 mm difference in each direction. The average dose difference at the predicted exhale position is less than 35 cGy between the models. Conclusions: The bronchial tree has little effect on the global deformation and the accuracy of deformable image registration of lungs. Hence, the homogenous model is a reasonable assumption. Since there are some local deformation differences between nodes as the material properties of the bronchial tree change that may affect the accuracy of dosimetric results, heterogeneity may be required for a smaller scale modeling of lungs.

Sensitivity of tumor motion simulation accuracy to lung biomechanical modeling approaches and parameters

“…We selected lung voxels as uniform material as previous studies showed that the homogeneous model was sufficient to model large scale lung deformation (Al-Mayah et al , 2010; Lai-Fook, 1981). The range of tumor motion magnitude and lung volume change (between end-inspiration and end-expiration) varied among the 8 different patients selected for the study.…”

Biomechanical deformable image registration of longitudinal lung CT images using vessel information

“…Al-Mayah et al (Adil Al-Mayah, Moseley, Velec, Hunter, et al 2010) previously demonstrated that incorporating the vessel tree in the FEM model with its own material properties had little effect on the global deformation. For this reason, the lung was considered in this study as a homogeneous organ and the additional conditions were placed on the closest node in the tetrahedral mesh of the lung.…”

Selecting registration schemes in case of interstitial lung disease follow‐up in CT

“…The intraobserver agreement was 0.930 ± 0.336 mm, similar with other studies. 17 Figure 5 depicts an application example of the selected registration schemes (scheme code: 30) at five representative anatomical levels of the lung. T III.…”