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Étude des facteurs influençant l'évaluation du comportement mécanique de l'os par tomodensitométrie

Dupuis, Karine (2007). Étude des facteurs influençant l'évaluation du comportement mécanique de l'os par tomodensitométrie. Mémoire de maîtrise électronique, Montréal, École de technologie supérieure.

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Résumé

La tomodensitométrie est utilisée pour estimer la densité osseuse et le comportement mécanique de l'os, mais des résultats variables sont rapportés dans la littérature et les sources de cette variabilité n'ont pas clairement été identifiées. Dans ce mémoire, l'acquisition d'images tomodensitométriques, des tests expérimentaux, des analyses par éléments finis et une étude de sensibilité ont été effectués sur des spécimens cadavériques et sur des modèles synthétiques pour étudier les facteurs influençant l'évaluation du comportement mécanique de l'os par tomodensitométrie. La principale source de variabilité identifiée provient de la relation utilisée pour attribuer les propriétés mécaniques de l'os en fonction du niveau de gris des images tomodensitométriques. Le degré d'anisotropie du modèle a également un effet significatif sur les résultats. La tomodensitométrie comporte certaines limites à estimer le comportement mécanique de l'os car sa résolution ne permet par d'évaluer la microstructure, qui a un effet significatif sur les propriétés mécaniques.

Titre traduit

Evaluation of the factors influencing the estimation of bone mechanical behavior using quantitative computed tomography

Résumé anglais

Quantitative computed tomography (QCT) is a powerful tool that makes the evaluation of bone density and the 3D reconstruction of bone geometry possible. Several studies have established relationships between bone density and its mechanical properties, and these relationships are used to personalize finite element models (FEM) developed to study bone mechanical behavior. The results obtained are variable and the reasons of these discrepancies have not been clearly identified. The main objective of this thesis is to study the factors that have an influence on the estimation of bone mechanical behavior using QCT. Four specific objectives are proposed to answer the main objective: 1- to establish relationships between the grey level of tomographic (CT) images, the apparent density (Papp) and the elastic modulus (E) of vertebral bone, 2- to develop a personalized finite element model of a vertebral body, 3- to perform a sensitivity study on the model and 4- to study the influence of the microstructure of synthetic parts on their mechanical properties.

Porcine vertebral bodies (VB) and calibration phantoms were imaged using a CT scanner. A relationship between the grey level (CT#) of CT images and the apparent density was established from the calibration phantoms images. Fifteen bone cores were extracted from the vertebral bodies and a corresponding region of interest was identified on the CT images to obtain their CT#. Their density was estimated using the CT# - Papp relationship. The bone cores were tested in compression to measure their elastic modulus and a relationship between papp and E was established. CT images of three vertebral bodies were obtained. The 3D reconstruction of their geometry was obtained and a finite element model was created. Elastic modulus was attributed to the model using the CT# - papp and papp - E relationships. Uniaxial compression was simulated and the model stiffness (KFEM) was estimated. Experimental compression testing was performed on the three vertebral bodies and the experimental stiffness measured (Kexp) was compared with KFEM· A sensitivity study of the model and a study on the influence of microstructure on mechanical properties were also realized.

A strong linear relationship was established between CT# and Papp: Papp = 0,0007CT# + 0,0276 (R2=0,9987). A moderate power relationship was established between papp and E : E =
3936 Pap/1.23 (R2=0,5636). The model overestimated Kexp by a factor of 2 (KFEM=20,1 kN/mm; Kexp=9,9 kN/mm). The elastic modulus attributed to the model is the parameter that has the strongest effect on the estimation of the stiffness. Homogeneity of the attribution and degree of anisotropy have a significant effect on the estimation of von Mises stress. QCT resolution does not allow the evaluation of bone microstructure, which has a significant effect on mechanical properties.

The moderate correlation between Papp and E is explained by experimental errors, uncertainties related to the specimens and by the QCT limitation to evaluate bone microstructure. The uncertainties in this relationship may explain in part the discrepancies between KFEM and Kexp· The finite element model could be improved if bone microstructure could be taken into account. This thesis has allowed the identification of the factors that influence the estimation of bone mechanical behavior using QCT and recommendations have been made to improve the method used. The improved method could eventually be used to model the bone - implant interaction of a patient instrumented vertebral segment or to simulate bone fracture apparition.

Type de document: Mémoire ou thèse (Mémoire de maîtrise électronique)
Renseignements supplémentaires: "Mémoire présenté à l'École de technologie supérieure comme exigence partielle à l'obtention de la maîtrise en génie." Bibliogr. : f. [143]-151.
Mots-clés libres: Colonne, Comportement, Element, Evaluation, Facteur, Fini, Mecanique, Modele, Os, Propriete, Thoracolombaire, Tomodensitometrie
Directeur de mémoire/thèse:
Directeur de mémoire/thèse
Petit, Yvan
Programme: Maîtrise en ingénierie > Génie
Date de dépôt: 08 avr. 2011 18:12
Dernière modification: 11 nov. 2016 01:17
URI: http://espace.etsmtl.ca/id/eprint/576

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