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This paper presents the application of the Cell Method (CM) to the static analysis of 3D structures obtained from micro-computed
tomography reconstructions of trabecular bone. The CM is a recently introduced numerical method, based on a direct discrete
formulation of equilibrium equations, which is particularly promising for the analysis of complex structures. In fact, due
to the direct discrete approach employed, no restriction is imposed by differentiability conditions and the characteristic
length of the elementary cell of the discretization can be of the same order of magnitude as the heterogeneities of the structure.
The same 3D microstructures used for the numerical simulations were reproduced by means of a rapid prototyping process, by
selective laser sintering of polyamide powder. The compression elastic modulus of the replicas was experimentally determined
and used as parameter for comparison with the simulations results. The experimental values are in good agreement with the
numerical ones, thus validating the methodology employed. 相似文献
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Krug R Carballido-Gamio J Burghardt AJ Haase S Sedat JW Moss WC Majumdar S 《Magnetic resonance imaging》2007,25(3):392-398
Trabecular bone structure and bone density contribute to the strength of bone and are important in the study of osteoporosis. Wavelets are a powerful tool in characterizing and quantifying texture in an image. The purpose of this study was to validate wavelets as a tool in computing trabecular bone thickness directly from gray-level images. To this end, eight cylindrical cores of vertebral trabecular bone were imaged using 3-T magnetic resonance imaging (MRI) and micro-computed tomography (microCT). Thickness measurements of the trabecular bone from the wavelet-based analysis were compared with standard 2D structural parameters analogous to bone histomorphometry (MR images) and direct 3D distance transformation methods (microCT images). Additionally, bone volume fraction was determined using each method. The average difference in trabecular thickness between the wavelet and standard methods was less than the size of 1 pixel size for both MRI and microCT analysis. A correlation (R) of .94 for microCT measurements and that of .52 for MRI were found for the bone volume fraction. Based on these results, we conclude that wavelet-based methods deliver results comparable with those from established MR histomorphometric measurements. Because the wavelet transform is more robust with respect to image noise and operates directly on gray-level images, it could be a powerful tool for computing structural bone parameters from MR images acquired using high resolution and thus limited signal scenarios. 相似文献
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Surfactant-templated mesoporous silica aerogels (or nanofoams) with their entire skeletal framework nanoencapsulated conformally by a thin polyurea layer are emerging as materials with high specific strength and high energy absorption. In this paper a modified split Hopkinson pressure bar was used to investigate their mechanical behavior under dynamic compression at high strain rates. The evolution of the mesoporous structure under such dynamic impact conditions was simulated using the Material Point Method (MPM). The material point model was generated from X-ray micro-computed tomography whereas each voxel was converted to a material point corresponding to the local skeletal density of the material. Simulation results agree well with the experimental data, indicating that the MPM can effectively model the compression of complex mesoporous structures. Simulations indicate a nearly uniform deformation at all three stages of compression: the elastic region, compaction and the final densification due to the low ratio of pore size to wall thickness and random distribution of the pores. Simulations have also indentified the function of the conformal polymer coating as a reinforcing factor, showing that different porosities, obtained by varying the skeletal wall thickness, affect the local stress distribution. Eventually, simulations confirm that the stress-strain behavior of aerogels under compression follows a power-law relationship with the initial bulk density, consistent with experimental results. 相似文献
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Pinney JR Taylor C Doan R Burghardt AJ Li X Kim HT Benjamin Ma C Majumdar S 《Magnetic resonance imaging》2012,30(2):271-282
Objective
The development of osteoarthritis following traumatic anterior cruciate ligament (ACL) injury is well established. However, few reliable indicators of early osteoarthritic changes have been established, which has limited the development of effective therapies. T1ρ and T2 mapping techniques have the ability to provide highly accurate and quantitative measurements of articular cartilage degeneration in vivo. Relating these cartilaginous changes to high-resolution bone-densitometric evaluations of the late-stage osteoarthritic bone is crucial in elucidating the mechanisms of development of traumatic osteoarthritis (OA) and potential therapies for early- or late-stage intervention.Methods
Twelve rabbits were monitored with in vivo magnetic resonance imaging (MRI) scans following ACL transection surgery with a contralateral leg sham operation. Six of the rabbits were treated with oral doxycycline for the duration of the experiment. At 12 weeks, the excised knees from three animals from each group (n=6 overall) were subjected to micro-computed tomography (CT) analysis.Results
Consistent with previous studies, initial elevations in T1ρ and T2 values in ACL-transected animals were observed with relative normalization towards values see in sham-operated legs over the 12-week study. This biphasic pattern could hold diagnostic potential to differentiate osteoarthritic cartilage by tracking the relative proportions of T1ρ and T2 values as they rise with inflammation then fall as collagen and proteoglycan loss leads to further dehydration. The addition of doxycycline resulted in inconclusive, yet potentially interesting, cartilaginous changes in several compartments of the rabbit legs. Micro-CT studies demonstrated decreased bone densitometrics in ACL-transected knees. Correlation studies suggest that the cartilaginous changes may be associated with some aspects of bony change and the development of OA.Conclusion
We conclude that there are definite relationships between cartilaginous changes as seen on MRI and late-stage microstructural bony changes after traumatic ACL injury in rabbits. In addition, doxycycline may show promise in mitigating early-stage cartilage damage that may serve to lessen late-stage osteoarthritic changes. This study demonstrates the ability to track OA progression and therapeutic efficacy with imaging modalities in vivo. 相似文献6.
We present a dynamic particle-based model for direct pore-level modeling of incompressible viscous fluid flow in disordered porous media. The model is capable of simulating flow directly in three-dimensional high-resolution micro-CT images of rock samples. It is based on moving particle semi-implicit (MPS) method. We modify this technique in order to improve its stability for flow in porous media problems. Using the micro-CT image of a rock sample, the entire medium, i.e., solid and fluid, is discretized into particles. The incompressible Navier–Stokes equations are then solved for each particle using the MPS summations. The model handles highly irregular fluid–solid boundaries effectively. An algorithm to split and merge fluid particles is also introduced. To handle the computational load, we present a parallel version of the model that runs on distributed memory computer clusters. The accuracy of the model is validated against the analytical, numerical, and experimental data available in the literature. The validated model is then used to simulate both unsteady- and steady-state flow of an incompressible fluid directly in a representative elementary volume (REV) size micro-CT image of a naturally-occurring sandstone with 3.398 μm resolution. We analyze the quality and consistency of the predicted flow behavior and calculate absolute permeability using the steady-state flow rate. 相似文献
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In the present study, a novel evaluation method involving rapid prototyped (RP) technology and finite element (FE) analysis
was used to study the elastic mechanical characteristics of human vertebral trabecular bone. Three-dimensional (3D) geometries
of the RP and FE models were obtained from the central area of vertebral bones of female cadavers, age 70 and 85. RP and FE
models were generated from the same high-resolution micro-computed tomography (μCT) scan data. We utilized RP technology along
with FE analysis based on μCT for high-resolution vertebral trabecular bone specimens. RP models were used to fabricate complex
3D objects of vertebral trabecular bone that were created in a fused deposition modeling machine. RP models of vertebral trabecular
bone are advantageous, particularly considering the repetition, risks, and ethical issues involved in using real bone from
cadaveric specimens. A cubic specimen with a side length of 6.5 mm or a cylindrical specimen with a 7 mm diameter and 5 mm
length proved better than a universal cubic specimen with a side length of 4 mm for the evaluation of elastic mechanical characteristics
of vertebral trabecular bones through experimental and simulated compression tests. The results from the experimental compression
tests of RP models closely matched those predicted by the FE models, and thus provided substantive corroboration of all three
approaches (experimental tests using RP models and simulated tests using FE models with ABS and trabecular bone material properties).
The RP technique combined with FE analysis has potential for widespread biomechanical use, such as the fabrication of dummy
human skeleton systems for the investigation of elastic mechanical characteristics of various bones. 相似文献
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