An Optical Flow Based Approach to Validating Dynamic Structural Finite Element Models of Biological Organs Using 4D Medical Images - the Aortic Valve as an Example

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Title: An Optical Flow Based Approach to Validating Dynamic Structural Finite Element Models of Biological Organs Using 4D Medical Images - the Aortic Valve as an Example
Authors: Gibney, Emma
Date: 2021-11-25
Abstract: Recent developments within the biomedical engineering field of using finite element methods to analyze biological structures has resulted in a need for a standardized method to validate these models. The purpose of this thesis was to develop a system to effectively and efficiently validate biological finite element models using 4D medical images. The aortic valve was chosen as the biological model for testing as any solution that could manage the complexity of the valve’s motion would likely work for simpler biological models. The proposed validation method involved 3 steps: estimating a voxel displacement field using a direct method of 3D motion estimation, converting the voxel displacement field into a nodal displacement field, and validating the results of a finite element model by comparing the nodal displacement field of the finite element model to the nodal displacement field from the medical images. The proposed validation method was implemented using synthetic 4D CT images of an aortic valve based on an existing finite element model, where the ground truth was the results of the existing finite element model. Three different direct motion estimation methods were implemented within the first step of the method and compared. The three methods were: 3D Horn-Schunck optical flow, 3D Brox optical flow, and demons method. The addition of a multilevel scheme with a variable scale constant was integrated into each of these motion estimation methods so that larger magnitudes of displacement could by captured. It was found that Horn-Schunck optical flow was best able to capture the motion of the aortic valve throughout a cardiac cycle. The proposed method of validation was able to track the aorta nodes effectively through an entire cardiac cycle and was able to track leaflet nodes through large displacements until the valve closed. Although the general trend of the motion of the aortic valve was captured by the validation method using synthetic medical images, node-to-node comparison was not entirely reliable. Comparison of the general trend was still superior to the current validation methods for biological finite element methods as it considered the motion of the entire structure.
URL: http://hdl.handle.net/10393/42971
http://dx.doi.org/10.20381/ruor-27188
CollectionThèses, 2011 - // Theses, 2011 -
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