The Experts below are selected from a list of 1305 Experts worldwide ranked by ideXlab platform
Hanna Isaksson - One of the best experts on this subject based on the ideXlab platform.
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Automated segmentation of cortical and trabecular Bone to generate finite element models for femoral Bone Mechanics.
Medical engineering & physics, 2019Co-Authors: Sami P. Väänänen, Lorenzo Grassi, Jukka S. Jurvelin, Mikko S. Venäläinen, Hanna Matikka, Yi Zheng, Hanna IsakssonAbstract:Finite element (FE) models based on quantitative computed tomography (CT) images are better predictors of Bone strength than conventional areal Bone mineral density measurements. However, FE models require manual segmentation of the femur, which is not clinically applicable. This study developed a method for automated FE analyses from clinical CT images. Clinical in-vivo CT images of 13 elderly female subjects were collected to evaluate the method. Secondly, proximal cadaver femurs were harvested and imaged with clinical CT (N = 17). Of these femurs, 14 were imaged with µCT and three had earlier been tested experimentally in stance-loading, while collecting surface deformations with digital image correlation. Femurs were segmented from clinical CT images using an automated method, based on the segmentation tool Stradwin. The method automatically distinguishes trabecular and cortical Bone, corrects partial volume effect and generates input for FE analysis. The manual and automatic segmentations agreed within about one voxel for in-vivo subjects (0.99 ± 0.23 mm) and cadaver femurs (0.21 ± 0.07 mm). The strains from the FE predictions closely matched with the experimentally measured strains (R2 = 0.89). The method can automatically generate meshes suitable for FE analysis. The method may bring us one step closer to enable clinical usage of patient-specific FE analyses.
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generation of 3d shape density cortical thickness and finite element mesh of proximal femur from a dxa image
Medical Image Analysis, 2015Co-Authors: Sami P. Väänänen, Lorenzo Grassi, Jukka S. Jurvelin, Gunnar Flivik, Hanna IsakssonAbstract:Areal Bone mineral density (aBMD), as measured by dual-energy X-ray absorptiometry (DXA), predicts hip fracture risk only moderately. Simulation of Bone Mechanics based on DXA imaging of the proximal femur, may help to improve the prediction accuracy. Therefore, we collected three (1-3) image sets, including CT images and DXA images of 34 proximal cadaver femurs (set1, including 30 males, 4 females), 35 clinical patient CT images of the hip (set 2, including 27 males, 8 females) and both CT and DXA images of clinical patients (set 3, including 12 female patients). All CT images were segmented manually and landmarks were placed on both femurs and pelvises. Two separate statistical appearance models (SAMs) were built using the CT images of the femurs and pelvises in sets 1 and 2, respectively. The 3D shape of the femur was reconstructed from the DXA image by matching the SAMs with the DXA images. The orientation and modes of variation of the SAMs were adjusted to minimize the sum of the absolute differences between the projection of the SAMs and a DXA image. The mesh quality and the location of the SAMs with respect to the manually placed control points on the DXA image were used as additional constraints. Then, finite element (FE) models were built from the reconstructed shapes. Mean point-to-surface distance between the reconstructed shape and CT image was 1.0mm for cadaver femurs in set 1 (leave-one-out test) and 1.4mm for clinical subjects in set 3. The reconstructed volumetric BMD showed a mean absolute difference of 140 and 185mg/cm3 for set 1 and set 3 respectively. The generation of the SAM and the limitation of using only one 2D image were found to be the most significant sources of errors in the shape reconstruction. The noise in the DXA images had only small effect on the accuracy of the shape reconstruction. DXA-based FE simulation was able to explain 85% of the CT-predicted strength of the femur in stance loading. The present method can be used to accurately reconstruct the 3D shape and internal density of the femur from 2D DXA images. This may help to derive new information from clinical DXA images by producing patient-specific FE models for mechanical simulation of femoral Bone Mechanics. (Less)
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Extracting accurate strain measurements in Bone Mechanics: A critical review of current methods.
Journal of the mechanical behavior of biomedical materials, 2015Co-Authors: Lorenzo Grassi, Hanna IsakssonAbstract:Osteoporosis related fractures are a social burden that advocates for more accurate fracture prediction methods. Mechanistic methods, e.g. finite element models, have been proposed as a tool to better predict Bone mechanical behaviour and strength. However, there is little consensus about the optimal constitutive law to describe Bone as a material. Extracting reliable and relevant strain data from experimental tests is of fundamental importance to better understand Bone mechanical properties, and to validate numerical models. Several techniques have been used to measure strain in experimental Mechanics, with substantial differences in terms of accuracy, precision, time- and length-scale. Each technique presents upsides and downsides that must be carefully evaluated when designing the experiment. Moreover, additional complexities are often encountered when applying such strain measurement techniques to Bone, due to its complex composite structure. This review of literature examined the four most commonly adopted methods for strain measurements (strain gauges, fibre Bragg grating sensors, digital image correlation, and digital volume correlation), with a focus on studies with Bone as a substrate material, at the organ and tissue level. For each of them the working principles, a summary of the main applications to Bone Mechanics at the organ- and tissue-level, and a list of pros and cons are provided. (Less)
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FUNCTIONAL IMAGING OF THE PROXIMAL FEMUR USING SHAPE TEMPLATE AND A Bone MINERAL DENSITY IMAGE
ASME 2011 Summer Bioengineering Conference Parts A and B, 2011Co-Authors: Sami P. Väänänen, Hanna Isaksson, Jukka S. JurvelinAbstract:Measurement of Bone mineral density (BMD) by DXA (dual-energy X-ray absorptiometry) is generally considered to be the clinical gold standard to diagnose osteoporosis. However, BMD alone is only a moderate predictor of fracture risk. Finite element analyses (FEA) of Bone Mechanics can contribute to a more accurate prediction of fracture risk (Cody et al. 1999). However, CT imaging is relatively expensive and inflicts larger radiation doses on the patient.Copyright © 2011 by ASME
Lorenzo Grassi - One of the best experts on this subject based on the ideXlab platform.
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Automated segmentation of cortical and trabecular Bone to generate finite element models for femoral Bone Mechanics.
Medical engineering & physics, 2019Co-Authors: Sami P. Väänänen, Lorenzo Grassi, Jukka S. Jurvelin, Mikko S. Venäläinen, Hanna Matikka, Yi Zheng, Hanna IsakssonAbstract:Finite element (FE) models based on quantitative computed tomography (CT) images are better predictors of Bone strength than conventional areal Bone mineral density measurements. However, FE models require manual segmentation of the femur, which is not clinically applicable. This study developed a method for automated FE analyses from clinical CT images. Clinical in-vivo CT images of 13 elderly female subjects were collected to evaluate the method. Secondly, proximal cadaver femurs were harvested and imaged with clinical CT (N = 17). Of these femurs, 14 were imaged with µCT and three had earlier been tested experimentally in stance-loading, while collecting surface deformations with digital image correlation. Femurs were segmented from clinical CT images using an automated method, based on the segmentation tool Stradwin. The method automatically distinguishes trabecular and cortical Bone, corrects partial volume effect and generates input for FE analysis. The manual and automatic segmentations agreed within about one voxel for in-vivo subjects (0.99 ± 0.23 mm) and cadaver femurs (0.21 ± 0.07 mm). The strains from the FE predictions closely matched with the experimentally measured strains (R2 = 0.89). The method can automatically generate meshes suitable for FE analysis. The method may bring us one step closer to enable clinical usage of patient-specific FE analyses.
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generation of 3d shape density cortical thickness and finite element mesh of proximal femur from a dxa image
Medical Image Analysis, 2015Co-Authors: Sami P. Väänänen, Lorenzo Grassi, Jukka S. Jurvelin, Gunnar Flivik, Hanna IsakssonAbstract:Areal Bone mineral density (aBMD), as measured by dual-energy X-ray absorptiometry (DXA), predicts hip fracture risk only moderately. Simulation of Bone Mechanics based on DXA imaging of the proximal femur, may help to improve the prediction accuracy. Therefore, we collected three (1-3) image sets, including CT images and DXA images of 34 proximal cadaver femurs (set1, including 30 males, 4 females), 35 clinical patient CT images of the hip (set 2, including 27 males, 8 females) and both CT and DXA images of clinical patients (set 3, including 12 female patients). All CT images were segmented manually and landmarks were placed on both femurs and pelvises. Two separate statistical appearance models (SAMs) were built using the CT images of the femurs and pelvises in sets 1 and 2, respectively. The 3D shape of the femur was reconstructed from the DXA image by matching the SAMs with the DXA images. The orientation and modes of variation of the SAMs were adjusted to minimize the sum of the absolute differences between the projection of the SAMs and a DXA image. The mesh quality and the location of the SAMs with respect to the manually placed control points on the DXA image were used as additional constraints. Then, finite element (FE) models were built from the reconstructed shapes. Mean point-to-surface distance between the reconstructed shape and CT image was 1.0mm for cadaver femurs in set 1 (leave-one-out test) and 1.4mm for clinical subjects in set 3. The reconstructed volumetric BMD showed a mean absolute difference of 140 and 185mg/cm3 for set 1 and set 3 respectively. The generation of the SAM and the limitation of using only one 2D image were found to be the most significant sources of errors in the shape reconstruction. The noise in the DXA images had only small effect on the accuracy of the shape reconstruction. DXA-based FE simulation was able to explain 85% of the CT-predicted strength of the femur in stance loading. The present method can be used to accurately reconstruct the 3D shape and internal density of the femur from 2D DXA images. This may help to derive new information from clinical DXA images by producing patient-specific FE models for mechanical simulation of femoral Bone Mechanics. (Less)
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Extracting accurate strain measurements in Bone Mechanics: A critical review of current methods.
Journal of the mechanical behavior of biomedical materials, 2015Co-Authors: Lorenzo Grassi, Hanna IsakssonAbstract:Osteoporosis related fractures are a social burden that advocates for more accurate fracture prediction methods. Mechanistic methods, e.g. finite element models, have been proposed as a tool to better predict Bone mechanical behaviour and strength. However, there is little consensus about the optimal constitutive law to describe Bone as a material. Extracting reliable and relevant strain data from experimental tests is of fundamental importance to better understand Bone mechanical properties, and to validate numerical models. Several techniques have been used to measure strain in experimental Mechanics, with substantial differences in terms of accuracy, precision, time- and length-scale. Each technique presents upsides and downsides that must be carefully evaluated when designing the experiment. Moreover, additional complexities are often encountered when applying such strain measurement techniques to Bone, due to its complex composite structure. This review of literature examined the four most commonly adopted methods for strain measurements (strain gauges, fibre Bragg grating sensors, digital image correlation, and digital volume correlation), with a focus on studies with Bone as a substrate material, at the organ and tissue level. For each of them the working principles, a summary of the main applications to Bone Mechanics at the organ- and tissue-level, and a list of pros and cons are provided. (Less)
X. Sherry Liu - One of the best experts on this subject based on the ideXlab platform.
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Effects of reproduction on sexual dimorphisms in rat Bone Mechanics.
Journal of biomechanics, 2018Co-Authors: Chantal M. J. De Bakker, Hongbo Zhao, Wei-ju Tseng, Allison R. Altman-singles, Yang Liu, Laurel Leavitt, X. Sherry LiuAbstract:Osteoporosis most commonly affects postmenopausal women. Although men are also affected, women over 65 are 6 times more likely to develop osteoporosis than men of the same age. This is largely due to accelerated Bone remodeling after menopause; however, the peak Bone mass attained during young adulthood also plays an important role in osteoporosis risk. Multiple studies have demonstrated sexual dimorphisms in peak Bone mass, and additionally, the female skeleton is significantly altered during pregnancy/lactation. Although clinical studies suggest that a reproductive history does not increase the risk of developing postmenopausal osteoporosis, reproduction has been shown to induce long-lasting alterations in maternal Bone structure and Mechanics, and the effects of pregnancy and lactation on maternal peak Bone quality are not well understood. This study compared the structural and mechanical properties of male, virgin female, and post-reproductive female rat Bone at multiple skeletal sites and at three different ages. We found that virgin females had a larger quantity of trabecular Bone with greater trabecular number and more plate-like morphology, and, relative to their body weight, had a greater cortical Bone size and greater Bone strength than males. Post-reproductive females had altered trabecular microarchitecture relative to virgins, which was highly similar to that of male rats, and showed similar cortical Bone size and Bone Mechanics to virgin females. This suggests that, to compensate for future reproductive Bone losses, females may start off with more trabecular Bone than is mechanically necessary, which may explain the paradox that reproduction induces long-lasting changes in maternal Bone without increasing postmenopausal fracture risk.
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Clinical Evaluation of Bone Strength and Fracture Risk
Current Osteoporosis Reports, 2017Co-Authors: Chantal M. J. De Bakker, Hongbo Zhao, Wei-ju Tseng, X. Sherry LiuAbstract:Purpose of Review This paper seeks to evaluate and compare recent advances in the clinical assessment of the changes in Bone mechanical properties that take place as a result of osteoporosis and other metabolic Bone diseases and their treatments. Recent Findings In addition to the standard of DXA-based areal Bone mineral density (aBMD), a variety of methods, including imaging-based structural measurements, finite element analysis (FEA)-based techniques, and alternate methods including ultrasound, Bone biopsy, reference point indentation, and statistical shape and density modeling, have been developed which allow for reliable prediction of Bone strength and fracture risk. These methods have also shown promise in the evaluation of treatment-induced changes in Bone mechanical properties. Summary Continued technological advances allowing for increasingly high-resolution imaging with low radiation dose, together with the expanding adoption of DXA-based predictions of Bone structure and Mechanics, as well as the increasing awareness of the importance of Bone material properties in determining whole-Bone Mechanics, lead us to anticipate substantial future advances in this field.
David P. Fyhrie - One of the best experts on this subject based on the ideXlab platform.
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Analysis of miniature single- and double-notch bending specimens for estimating the fracture toughness of cortical Bone.
Journal of biomedical materials research. Part A, 2012Co-Authors: Jordan Mccormack, Xiang S. Wang, Susan M. Stover, J. C. Gibeling, David P. FyhrieAbstract:Studies of the fracture behavior of cortical Bone have determined multiple toughening mechanisms that are active during propagation of a crack. Common methods for measuring Bone fracture toughness use single-notched specimens often in four-point (SN4PB) or three-point bending (SN3PB). A double-notch four-point bending (DN4PB) specimen is useful to study prefailure damage at the crack tip. Total failure occurs at one notch and only partial failure at the other allowing study of prefailure damage in the unbroken notch. There is no widely known method for calculating the fracture toughness of Bone using a DN4PB specimen. A method for calculating the fracture toughness of cortical Bone using a DN4PB is developed here and compared with results for a common SN3PB specimen. The new double-notch method permits using a single specimen to measure apparent fracture toughness and to study both pre- and postfailure microdamage in the Bone matrix. When and how to use the new and the established test specimens for understanding Bone Mechanics is discussed. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A:, 2012.
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Application of homogenization theory to the study of trabecular Bone Mechanics
Journal of biomechanics, 1991Co-Authors: Scott J. Hollister, David P. Fyhrie, Karl J. Jepsen, Steven A. GoldsteinAbstract:Aha& strain. At this time, however, there is no generally accepted (or easily accomplished) technique for predicting the effect of microstructure on trabecular Bone apparent stiffness and strength or estimating tissue level stress or strain. In this paper, a recently developed Mechanics theory specifically designed to analyze microstructured materials, called the homogenization theory, is presented and applied to analyze trabecular Bone Mechanics. Using the homogenization theory it is possible to perform microstructural and continuum analyses separately and then combine them in a systematic manner. Stiffness predictions from two different microstructural models of trabecular Bone show reasonable agreement with experimental results, depending on metaphyseal region, (R”>0.5 for proximai humerus specimens, R* ~0.5 for distal femur and proximal tibia specimens). Estimates of both microstructural strain energy density (SED) and apparent SED show that there are large differences (up to 30 times) between apparent SED (as calculated by standard continuum finite element analyses) and the maximum microstructural or tissue SED. Furthermore, a strut and spherical void microstructure gave very different estimates of maximum tissue SED for the same Bone volume fraction (BV/TV). The estimates from the spherical void microstructure are between 2 and 20 times greater than the strut microstructure at lo-20% W/TV
Steven A. Goldstein - One of the best experts on this subject based on the ideXlab platform.
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Application of homogenization theory to the study of trabecular Bone Mechanics
Journal of biomechanics, 1991Co-Authors: Scott J. Hollister, David P. Fyhrie, Karl J. Jepsen, Steven A. GoldsteinAbstract:Aha& strain. At this time, however, there is no generally accepted (or easily accomplished) technique for predicting the effect of microstructure on trabecular Bone apparent stiffness and strength or estimating tissue level stress or strain. In this paper, a recently developed Mechanics theory specifically designed to analyze microstructured materials, called the homogenization theory, is presented and applied to analyze trabecular Bone Mechanics. Using the homogenization theory it is possible to perform microstructural and continuum analyses separately and then combine them in a systematic manner. Stiffness predictions from two different microstructural models of trabecular Bone show reasonable agreement with experimental results, depending on metaphyseal region, (R”>0.5 for proximai humerus specimens, R* ~0.5 for distal femur and proximal tibia specimens). Estimates of both microstructural strain energy density (SED) and apparent SED show that there are large differences (up to 30 times) between apparent SED (as calculated by standard continuum finite element analyses) and the maximum microstructural or tissue SED. Furthermore, a strut and spherical void microstructure gave very different estimates of maximum tissue SED for the same Bone volume fraction (BV/TV). The estimates from the spherical void microstructure are between 2 and 20 times greater than the strut microstructure at lo-20% W/TV
