scholarly journals A New Material Mapping Procedure for Quantitative Computed Tomography-Based, Continuum Finite Element Analyses of the Vertebra

2011 ◽  
Vol 133 (7) ◽  
Author(s):  
Ginu U. Unnikrishnan ◽  
Elise F. Morgan
Keyword(s):  
Computed Tomography ◽  
Bone Mineral Density ◽  
Finite Element ◽  
Material Properties ◽  
Quantitative Computed Tomography ◽  
Block Size ◽  
Finite Element Models ◽  
Finite Element Analyses ◽  
Mineral Density ◽  
Mapping Procedure

Inaccuracies in the estimation of material properties and errors in the assignment of these properties into finite element models limit the reliability, accuracy, and precision of quantitative computed tomography (QCT)-based finite element analyses of the vertebra. In this work, a new mesh-independent, material mapping procedure was developed to improve the quality of predictions of vertebral mechanical behavior from QCT-based finite element models. In this procedure, an intermediate step, called the material block model, was introduced to determine the distribution of material properties based on bone mineral density, and these properties were then mapped onto the finite element mesh. A sensitivity study was first conducted on a calibration phantom to understand the influence of the size of the material blocks on the computed bone mineral density. It was observed that varying the material block size produced only marginal changes in the predictions of mineral density. Finite element (FE) analyses were then conducted on a square column-shaped region of the vertebra and also on the entire vertebra in order to study the effect of material block size on the FE-derived outcomes. The predicted values of stiffness for the column and the vertebra decreased with decreasing block size. When these results were compared to those of a mesh convergence analysis, it was found that the influence of element size on vertebral stiffness was less than that of the material block size. This mapping procedure allows the material properties in a finite element study to be determined based on the block size required for an accurate representation of the material field, while the size of the finite elements can be selected independently and based on the required numerical accuracy of the finite element solution. The mesh-independent, material mapping procedure developed in this study could be particularly helpful in improving the accuracy of finite element analyses of vertebroplasty and spine metastases, as these analyses typically require mesh refinement at the interfaces between distinct materials. Moreover, the mapping procedure is not specific to the vertebra and could thus be applied to many other anatomic sites.

scholarly journals Effect of Specimen-Specific Anisotropic Material Properties in Quantitative Computed Tomography-Based Finite Element Analysis of the Vertebra

2013 ◽  
Vol 135 (10) ◽  
Author(s):  
Ginu U. Unnikrishnan ◽  
Glenn D. Barest ◽  
David B. Berry ◽  
Amira I. Hussein ◽  
Elise F. Morgan
Keyword(s):  
Computed Tomography ◽  
Finite Element ◽  
Mechanical Behavior ◽  
Vertebral Body ◽  
Material Properties ◽  
Anisotropic Material ◽  
Quantitative Computed Tomography ◽  
Large Contribution ◽  
Mineral Density ◽  
Peripheral Regions

Intra- and inter-specimen variations in trabecular anisotropy are often ignored in quantitative computed tomography (QCT)-based finite element (FE) models of the vertebra. The material properties are typically estimated solely from local variations in bone mineral density (BMD), and a fixed representation of elastic anisotropy (“generic anisotropy”) is assumed. This study evaluated the effect of incorporating specimen-specific, trabecular anisotropy on QCT-based FE predictions of vertebral stiffness and deformation patterns. Orthotropic material properties estimated from microcomputed tomography data (“specimen-specific anisotropy”), were assigned to a large, columnar region of the L1 centrum (n = 12), and generic-anisotropic material properties were assigned to the remainder of the vertebral body. Results were compared to FE analyses in which generic-anisotropic properties were used throughout. FE analyses were also performed on only the columnar regions. For the columnar regions, the axial stiffnesses obtained from the two categories of material properties were uncorrelated with each other (p = 0.604), and the distributions of minimum principal strain were distinctly different (p ≤ 0.022). In contrast, for the whole vertebral bodies in both axial and flexural loading, the stiffnesses obtained using the two categories of material properties were highly correlated (R2 > 0.82, p < 0.001) with, and were no different (p > 0.359) from, each other. Only moderate variations in strain distributions were observed between the two categories of material properties. The contrasting results for the columns versus vertebrae indicate a large contribution of the peripheral regions of the vertebral body to the mechanical behavior of this bone. In companion analyses on the effect of the degree of anisotropy (DA), the axial stiffnesses of the trabecular column (p < 0.001) and vertebra (p = 0.007) increased with increasing DA. These findings demonstrate the need for accurate modeling of the peripheral regions of the vertebral body in analyses of the mechanical behavior of the vertebra.

scholarly journals Experimental investigation of bone mineral density in Thoroughbreds using quantitative computed tomography

2015 ◽  
Vol 26 (3) ◽  
pp. 81-87 ◽  
Author(s):  
Kazutaka YAMADA ◽  
Fumio SATO ◽  
Tohru HIGUCHI ◽  
Kaori NISHIHARA ◽  
Mitsunori KAYANO ◽  
...  
Keyword(s):  
Computed Tomography ◽  
Bone Mineral Density ◽  
Experimental Investigation ◽  
Bone Mineral ◽  
Quantitative Computed Tomography ◽  
Mineral Density

Effect of Rheumatoid Arthritis on Volumetric Bone Mineral Density and Bone Geometry, Assessed by Peripheral Quantitative Computed Tomography in Postmenopausal Women Treated with Bisphosphonates

2012 ◽  
Vol 39 (6) ◽  
pp. 1215-1220 ◽  
Author(s):  
SYMEON TOURNIS ◽  
VASILIOS SAMDANIS ◽  
SAVAS PSARELIS ◽  
CHRYSA LIAKOU ◽  
JULIA ANTONIOU ◽  
...  
Keyword(s):  
Rheumatoid Arthritis ◽  
Computed Tomography ◽  
Bone Mineral Density ◽  
Postmenopausal Women ◽  
Bone Mineral ◽  
Quantitative Computed Tomography ◽  
Bone Geometry ◽  
Peripheral Quantitative Computed Tomography ◽  
Volumetric Bone Mineral Density ◽  
Mineral Density

Objective.To investigate the effect of rheumatoid arthritis (RA) on volumetric bone mineral density (vBMD) and bone geometry in postmenopausal women treated with bisphosphonates.Methods.Fifty-three postmenopausal women with RA and 87 control subjects, comparable in terms of age, body mass index, and years since menopause, underwent peripheral quantitative computed tomography (pQCT) of the nondominant tibia.Results.At 4% (trabecular site), trabecular bone mineral content (BMC) and vBMD (p < 0.001) were lower in the RA group, while trabecular area was comparable. At 38% (cortical site), cortical BMC (p < 0.01), area (p < 0.05), and thickness (p < 0.001) were lower in the RA group, whereas vBMD was comparable. Endosteal circumference was higher (p < 0.05), whereas periosteal circumference was comparable, indicating cancellization of cortical bone. In the RA group, muscle area was lower (p < 0.001), while at 14% polar stress strength index was significantly lower (p < 0.01) in patients with RA, indicating impairment of bone mechanical properties.Conclusion.RA is associated with negative effects on both cortical and cancellous bone in postmenopausal women treated with bisphosphonates. Cortical geometric properties are also adversely affected mainly by increased endosteal circumference, whereas trabecular geometric properties are generally preserved.

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