micro-CT Image Data Research Articles

Multidimensional characterization of particle morphology and mineralogical composition using CT data and R-vine copulas

Computed tomography (CT) can capture volumes large enough to measure a statistically meaningful number of micron-sized particles with a sufficiently good resolution to allow for the analysis of individual particles. However, the development of methods to efficiently investigate such image data and interpretably model the observed particle features is still an active field of research. When image data of particles exhibiting a wide range of shapes and sizes is considered, traditional image segmentation methods, such as the classic watershed algorithm, struggle to recognize particles with satisfying accuracy. Thus, more advanced methods of machine learning must be utilized for image segmentation to improve the validity of subsequent analyses. Moreover, CT data does not include information about the mineralogical composition of particles and, therefore, additional SEM-EDS image data has to be acquired. In this paper, micro-CT image data of a particle system mostly consisting of zinnwaldite–quartz composites is considered. First, an image segmentation method is applied which uses deep convolutional neural networks, in particular an adaptation of the U-net architecture. This has the advantage of requiring less hand-labeling than other machine learning methods, while also being more flexible with the possibility of transfer learning. Then, fully parameterized models based on vine copulas are designed to determine multivariate probability distributions of descriptor vectors for the size, shape, texture and composition of particles—allowing for the estimation and interpretable characterization of interdependencies between particle descriptors. For model fitting, the segmented three-dimensional CT data and co-registered two-dimensional SEM-EDS data are used. The models are applied to predict the mineralogical composition of particles, solely on the basis of particle descriptors observed in CT data.

End-to-end prediction of uniaxial compression profiles of apples during in vitro digestion using time-series micro-computed tomography and deep learning

Machine learning is a promising technique to develop models, which extract relevant information from image data. This study applies convolutional neural networks trained end-to-end to predict the mechanical properties of apples (var. Granny Smith) from micro-CT image data collected during in vitro gastric digestion. Models were trained to directly output compression curves, allowing for representation of complex curve shapes, which changed throughout the digestion process. Models evaluated using 3-fold cross-validation demonstrated high predictive performance, with RMSE of 4.36 N and R2 of 0.939 compared to measured data. This performance was decreased to an RMSE of 14.3 N and R2 of 0.296 when applied to an out-of-distribution dataset. Saliency mapping used to interpret model output demonstrated a mechanistic link between typical biophysical tissue changes and model attention. Overall, the end-to-end deep learning approach represents a promising method for rapid, nondestructive evaluation of mechanical properties during food processing and digestion.

Brain Shape Provides a Structural Mechanism for Postorbital Septation in Primates

Postorbital septation is a character that unites haplorhine primates. As a result, evidence of postorbital septation is expected for fossil primates that may be ancestral to both modern tarsiers and modern anthropoids. Our previous work on newborn primates has indicated that postorbital septation in tarsiers is secondary to growth of their large eyes. If this is the case, postorbital septation is convergent in tarsiers and anthropoids, and therefore should not be expected in their fossil ancestors. Here, we used morphometric analysis of the cranium and endocast of newborn and adult primates to show that postorbital septation in the order Primates may be explained by shape of the brain.We used a sample of over thirty species of modern primates representing all major clades, with individuals representing both newborn and adult stages. The newborn stage is most informative for understanding spatial relationships of soft tissues during formation of the skull. MicroCT image data were used to create virtual reconstructions of the cranium and endocast as an estimate of brain shape. Fixed landmarks were used to capture the shape of the cranium, and sliding semilandmarks represented the contour of frontal and temporal lobes on the endocast. As expected, morphometric analysis showed a significant effect of phylogeny on cranial and endocast shape in both newborns and adults. Notably, the phylogenetic effect was apparent in only the contours of the frontal and temporal lobes, independent of cranial shape. We present 3D models of the endocast and cranium of newborn primates to illustrate the spatial relationship of brain and facial structures as a mechanism for postorbital septation in anthropoid primates.

Detection and Tracking Volumes of Interest in 3D Printed Tissue Engineering Scaffolds using 4D Imaging Modalities.

Additive manufacturing (AM) platforms allow the production of patient tissue engineering scaffolds with desirable architectures. Although AM platforms offer exceptional control on architecture, post-processing methods such as sintering and freeze-drying often deform the printed scaffold structure. In-situ 4D imaging can be used to analyze changes that occur during post-processing. Visualization and analysis of changes in selected volumes of interests (VOIs) over time are essential to understand the underlining mechanisms of scaffold deformations. Yet, automated detection and tracking of VOIs in the 3D printed scaffold over time using 4D image data is currently an unsolved image processing task. This paper proposes a new image processing technique to segment, detect and track volumes of interest in 3D printed tissue engineering scaffolds. The method is validated using a 4D synchrotron sourced microCT image data captured during the sintering of bioactive glass scaffolds in-situ. The proposed method will contribute to the development of scaffolds with controllable designs and optimum properties for the development of patient-specific scaffolds.

High resolution three-dimensional strain measurements in human articular cartilage

An unresolved challenge in osteoarthritis research is characterising the localised intra-tissue mechanical response of articular cartilage. The aim of this study was to explore whether laboratory micro-computed tomography (micro-CT) and digital volume correlation (DVC) permit non-destructive quantification of three-dimensional (3D) strain fields in human articular cartilage. Human articular cartilage specimens were harvested from the knee, mounted into a loading device and imaged in the unloaded and loaded states using a micro-CT scanner. Strain was measured throughout the cartilage volume using the micro-CT image data and DVC analysis. The volumetric DVC-measured strain was within 5% of the known applied strain. Variation in strain distribution between the superficial, middle and deep zones was observed, consistent with the different architecture of the material in these locations. These results indicate DVC method may be suitable for calculating strain in human articular cartilage.

CACCT: An Automated Tool of Detecting Complicated Cardiac Malformations in Mouse Models.

Congenital heart disease (CHD) is the major cause of morbidity/mortality in infancy and childhood. Using a mouse model to uncover the mechanism of CHD is essential to understand its pathogenesis. However, conventional 2D phenotyping methods cannot comprehensively exhibit and accurately distinguish various 3D cardiac malformations for the complicated structure of heart cavity. Here, a new automated tool based on microcomputed tomography (micro‐CT) image data sets known as computer‐assisted cardiac cavity tracking (CACCT) is presented, which can detect the connections between cardiac cavities and identify complicated cardiac malformations in mouse hearts automatically. With CACCT, researchers, even those without expert training or diagnostic experience of CHD, can identify complicated cardiac malformations in mice conveniently and precisely, including transposition of the great arteries, double‐outlet right ventricle and atypical ventricular septal defect, whose accuracy is equivalent to senior fetal cardiologists. CACCT provides an effective approach to accurately identify heterogeneous cardiac malformations, which will facilitate the mechanistic studies into CHD and heart development.

Effect of length of apical root resection on the biomechanical response of a maxillary central incisor in various occlusal relationships.

To investigate the stress distribution and tooth displacement of a maxillary central incisor with various apical root resection lengths and occlusal relationships using finite element (FE) analysis. A maxillary central incisor was scanned by micro-CT. First, the FE intact incisor model with dentine, enamel, pulp and root surrounded by alveolar bone and periodontal ligament was designed based on the micro-CT image data. Then, six FE models with varying lengths of apical root resection were established to simulate the clinical treatment and reveal the clinically applicable limit of apical root resection during endodontic microsurgery. For each model under different loading conditions, the maximum von Mises stress (σ max) at the root apex, root cervix, alveolar bone and periodontal ligament and the maximum tooth displacement (ΔR max) were calculated and compared. In a normal occlusion, more than 6mm of root resection resulted in a marked increase in the ΔR max values (>10%) and σ max values of alveolar bone (>50%); the stress levels at the root apex increased dramatically when the apical root was resected more than 7mm. With increased overjet, apical root resection did not change the stress level markedly until it reached 8mm, but the ΔR max increased markedly (>10%) if the root was resected more than 5mm. With deep overbites, the σ max increased significantly (>50%) when the root was resected more than 4mm whilst the ΔR max decreased. With increased overjet and deep overbite, more than 6mm of resection resulted in a substantial σ max increase (>50%) of alveolar bone and the ΔR max increased markedly (>10%) when the root was resected 8mm. Additionally, the σ max and the ΔR max values were greater with increased overjet and lower with deep overbites. Using FE analysis, apical root resection of more than 6mm resulted in a marked increase of stress distribution and tooth displacement in normal and increased overjet with deep overbite occlusal relationships. In increased overjets or deep overbites, more than 5mm or 4mm, respectively, stress distribution and tooth displacement increased markedly.

P9. Dimethyloxaloylglycine (DMOG) preconditioning of adipose-derived mesenchymal stem cells as strategy for enhancing posterolateral lumbar fusion in a rat model

BACKGROUND CONTEXT Transplantation of adipose-derived mesenchymal stem cells (ADSCs) has become a promising approach for bone regeneration therapies, particularly in elderly patients. However, poor cell survival in vivo after implantation due to the ischemic tissue environment has been one of the major limitations of the effectiveness of this strategy. Hypoxia Inducible Factor-1α (HIF-1α) plays an important role in angiogenic-osteogenic coupling during bone regeneration, as it is a critical mediator of the adaptive cell response to hypoxia. DMOG treatment has been demonstrated to stabilize cellular expression of HIF-1α in cells, as well as enhance osteogenic and angiogenic capacity of MSCs. By therapeutically targeting both osteogenesis and vascularization via DMOG preconditioned MSCs, this tissue-engineering approach sought to yield superior bone quality and integration, thereby increasing rates of spinal fusion. PURPOSE We aimed to demonstrate that preconditioning adipose (ADSC)-derived (AD) MSCs with DMOG prior to implantation will prolong survival in vivo and improve spinal fusion outcomes in a rat model. STUDY DESIGN/SETTING In vivo study via a rat posterolateral spinal fusion model. PATIENT SAMPLE Syngeneic 6-8 week old Lewis rats. OUTCOME MEASURES Manual palpation scoring was performed by blinded researchers as follows: 0 = non-fused; 1 = partial fusion, some motion across operative joint; and, 2 = fused, no motion across the operated joint. MicroCT images were used to assess fusion mass volume (mm^3) via ImageJ software and determine CT fusion score (0 = non-fused; 1 = unilateral fusion; 2 = bilateral fusion). METHODS ADSCs were isolated from the inguinal fat pads of syngeneic 6-8 week old Lewis rats and cultured in vitro. When passage 1 (P1) ADSCs reached approximately 80% confluency they were pre-conditioned for 24 hours with 1 ng of DMOG (Fisher Scientific). After pre-conditioning, 2 × 10^6 ADSCs were seeded onto Vitoss (Stryker) bone graft substitute scaffolds for subsequent transplantation. Posterolateral spinal fusion surgery at L4-L5 was performed on 18 female Lewis rats divided into 2 experimental groups: [1] Vitoss+ADSCs pre-conditioned with DMOG; and, [2] Vitoss+non pre-conditioned ADSCs. Fusion was evaluated eight weeks post-surgery. Manual palpation scoring evaluated the motion across the operated joint, and MicroCT images were assessed for fusion mass volume and CT fusion. RESULTS Preliminary microCT imaging data suggest that DMOG pre-conditioned ADSCs (n=12) yielded significantly higher fusion mass volumes than non-preconditioned ADSCs (n=6) (23.49 mm^3 vs. 15.39 mm^3, respectively, p=.001). DMOG pre-conditioned ADSCs showed a trend towards higher rates of fusion and manual palpation scores compared to non-conditioned ADSCs (1.16 vs. 0.50, respectively, p=.06; and 1.25 vs. 0.66, respectively, p>.05). CONCLUSIONS In our rat posterolateral fusion model, DMOG pre-conditioned ADSCs displayed an increased fusion mass volume, CT fusion rates, and manual palpation score compared to non-conditioned ADSCs. Ongoing histological studies will evaluate whether there are any differences in the quality of bone formed within the fusion masses. Future studies will also compare whether these results are also similar in bone marrow-derived MSCs. FDA DEVICE/DRUG STATUS Dimethyloxaloylglycine (Investigational/Not approved)

Evaluation of four instruments with different working motion using artificial plastic model with C-shaped single canal

The purpose of this study was to evaluate four instruments with different working motion for preparation of a C-shaped single canal wall using the same artificial plastic models reproduced from a human tooth. One tooth with root canal morphology C1 (the shape is an uninterrupted “C” with no separation or division) was selected among three-dimensional micro-computed tomography (micro-CT) imaging data of extracted human teeth. Imaging data were then converted into STL form data, and twenty-four C-shaped root canal model blocks were manufactured using this STL form data. These blocks were randomly divided into four groups of six blocks each and instrumented as follows: stainless steel K-files (SSK), Self-Adjusting File (SAF), ProTaper NEXT (PTN) and RECIPROC (REC). Micro-CT images taken before and after canal preparation were superimposed, and instrumented canal area, percentage of instrumented canal area, part of instrumented canal area, volume of instrumented canal and time taken for instrumentation were evaluated for each group. The greatest instrumented canal area, percentage of instrumented canal area and volume of instrumented canal were as follows (in decreasing order): SSK > SAF > PTN > REC (P < 0.05). The longest time taken for instrumentation was as follows (in decreasing order): SAF > SSK > PTN > REC (P < 0.05). The conscious shaping of SSK and the lattice structure of SAF were instrumented all root canal walls equally. PTN and REC required less time taken for instrumentation, but showed unequal instrumentation.

Meniscal Ossicles as micro-CT Imaging Biomarker in a Rodent Model of Antigen-Induced Arthritis: a Synchrotron-Based X-ray Pilot Study

It is increasingly recognized that early detection of bone erosion plays an important role in the overall evaluation of rheumatoid arthritis and in the choice of the correct treatment approach. Since an appropriate use of imaging biomarkers in preclinical settings offers the prospect of smaller and optimized sample size, in the present study we define an anatomical imaging biomarker that could be objectively measured from micro-CT imaging data as an indicator of bone erosion in arthritis process. The well-characterized antigen-induced arthritis (AIA) model in rats was used. The animals were divided into 2 groups: arthritic disease control and arthritic having been administrated with the tumor necrosis factor alpha-blocking agent (Humira). Rats were sacrificed in the acute phase of AIA; peripheral blood and synovial tissue were collected for assessment of arthritis. Ex vivo micro-CT tomography of knee joints was performed at the Elettra synchrotron light source (Trieste, Italy). Overall, results from this study suggest that use of high-resolution micro-CT analysis coupled with meniscal ossicles bone parameters quantification provide a powerful combination to enhance data interpretation and assessment of disease-modifying drugs in an animal model of arthritis.

Local diffusion coefficient measurements in shale using dynamic micro-computed tomography

Diffusion is an important mass transport mechanism in ultra-low permeability shale matrix and thus, characterization of shale diffusivity is of practical necessity for shale gas developments. We present a novel method for measuring bulk and local diffusion coefficients of shale core-plugs using dynamic X-ray micro-computed tomography (micro-CT). Liquid diffusion experiments are conducted on a centimeter-scale shale core and a series of time-sequenced 3D micro-CT images are acquired through dynamic imaging. Local diffusion coefficients are measured numerically from the micro-CT data using a new mathematical method that allows us to evaluate the heterogeneity of shale diffusivity at the sub-core scale. The variation of local diffusion coefficients is quantified using the Dykstra Parsons method, which provides a means to quantify core-scale heterogeneity in shale samples. Although the micro-CT image data may be influenced by noise, the presented technique provides reasonable results and our validation studies provide fundamental design parameters for measuring diffusivity values from dynamic micro-CT experiments. In addition the presented method can be applied to other porous materials where diffusion occurs.

Combined Near-infrared Fluorescent Imaging and Micro-computed Tomography for Directly Visualizing Cerebral Thromboemboli.

Direct thrombus imaging visualizes the root cause of thromboembolic infarction. Being able to image thrombus directly allows far better investigation of stroke than relying on indirect measurements, and will be a potent and robust vascular research tool. We use an optical imaging approach that labels thrombi with a molecular imaging thrombus marker- a Cy5.5 near-infrared fluorescent (NIRF) probe that is covalently linked to the fibrin strands of the thrombus by the fibrin-crosslinking enzymatic action of activated coagulation factor XIIIa during the process of clot maturation. A micro-computed tomography (microCT)-based approach uses thrombus-seeking gold nanoparticles (AuNPs) functionalized to target the major component of the clot: fibrin. This paper describes a detailed protocol for the combined in vivo microCT and ex vivo NIRF imaging of thromboemboli in a mouse model of embolic stroke. We show that in vivo microCT and fibrin-targeted glycol-chitosan AuNPs (fib-GC-AuNPs) can be used for visualizing both in situ thrombi and cerebral embolic thrombi. We also describe the use of in vivo microCT-based direct thrombus imaging to serially monitor the therapeutic effects of tissue plasminogen activator-mediated thrombolysis. After the last imaging session, we demonstrate by ex vivo NIRF imaging the extent and the distribution of residual thromboemboli in the brain. Finally, we describe quantitative image analyses of microCT and NIRF imaging data. The combined technique of direct thrombus imaging allows two independent methods of thrombus visualization to be compared: the area of thrombus-related fluorescent signal on ex vivo NIRF imaging vs. the volume of hyperdense microCT thrombi in vivo.

Combined Near-infrared Fluorescent Imaging and Micro-computed Tomography for Directly Visualizing Cerebral Thromboemboli

Direct thrombus imaging visualizes the root cause of thromboembolic infarction. Being able to image thrombus directly allows far better investigation of stroke than relying on indirect measurements, and will be a potent and robust vascular research tool. We use an optical imaging approach that labels thrombi with a molecular imaging thrombus marker — a Cy5.5 near-infrared fluorescent (NIRF) probe that is covalently linked to the fibrin strands of the thrombus by the fibrin-crosslinking enzymatic action of activated coagulation factor XIIIa during the process of clot maturation. A micro-computed tomography (microCT)-based approach uses thrombus-seeking gold nanoparticles (AuNPs) functionalized to target the major component of the clot: fibrin. This paper describes a detailed protocol for the combined in vivo microCT and ex vivo NIRF imaging of thromboemboli in a mouse model of embolic stroke. We show that in vivo microCT and fibrin-targeted glycol-chitosan AuNPs (fib-GC-AuNPs) can be used for visualizing both in situ thrombi and cerebral embolic thrombi. We also describe the use of in vivo microCT-based direct thrombus imaging to serially monitor the therapeutic effects of tissue plasminogen activator-mediated thrombolysis. After the last imaging session, we demonstrate by ex vivo NIRF imaging the extent and the distribution of residual thromboemboli in the brain. Finally, we describe quantitative image analyses of microCT and NIRF imaging data. The combined technique of direct thrombus imaging allows two independent methods of thrombus visualization to be compared: the area of thrombus-related fluorescent signal on ex vivo NIRF imaging vs. the volume of hyperdense microCT thrombi in vivo.

Predicting Trabecular Bone Stiffness from Clinical Cone-Beam CT and HR-pQCT Data; an In Vitro Study Using Finite Element Analysis.

Stiffness and shear moduli of human trabecular bone may be analyzed in vivo by finite element (FE) analysis from image data obtained by clinical imaging equipment such as high resolution peripheral quantitative computed tomography (HR-pQCT). In clinical practice today, this is done in the peripheral skeleton like the wrist and heel. In this cadaveric bone study, fourteen bone specimens from the wrist were imaged by two dental cone beam computed tomography (CBCT) devices and one HR-pQCT device as well as by dual energy X-ray absorptiometry (DXA). Histomorphometric measurements from micro-CT data were used as gold standard. The image processing was done with an in-house developed code based on the automated region growing (ARG) algorithm. Evaluation of how well stiffness (Young’s modulus E3) and minimum shear modulus from the 12, 13, or 23 could be predicted from the CBCT and HR-pQCT imaging data was studied and compared to FE analysis from the micro-CT imaging data. Strong correlations were found between the clinical machines and micro-CT regarding trabecular bone structure parameters, such as bone volume over total volume, trabecular thickness, trabecular number and trabecular nodes (varying from 0.79 to 0.96). The two CBCT devices as well as the HR-pQCT showed the ability to predict stiffness and shear, with adjusted R2-values between 0.78 and 0.92, based on data derived through our in-house developed code based on the ARG algorithm. These findings indicate that clinically used CBCT may be a feasible method for clinical studies of bone structure and mechanical properties in future osteoporosis research.

Phylogenetic signals in the primate sphenoid bone at birth

The sphenoid is often considered to be the keystone of the skull. Many cranial traits are used to distinguish phylogenetic groups among primates, and the sphenoid is an influential element in these differences. Because of the importance of the sphenoid for the integration of face, vault, and cranial base, we expected that many of these traits would be apparent early in cranial osteogenesis, establishing the framework for future development. We tested three specific hypotheses in neonate specimens of haplorhine and strepsirrhine primates. First, based on greater encephalization of haplorhine adult primates relative to strepsirrhine primates (and despite reports that haplorhines show pronounced brain growth postnatally), we predicted that the cranial base would show greater flexion in haplorhines. Second, based on expanded temporal lobes in haplorhines relative to strepsirrhines, we expected that the alisphenoid would be expanded in haplorhines. Third, based on orbital convergence of haplorhine adult primates, we predicted that the width of the presphenoid would be greater in strepsirrhine neonate primates relative to haplorhines.We evaluated perinatal (late fetal through six days postnatal) specimens of primates representing strepsirrhine and haplorhine taxa. MicroCT imaging data were used to create 3D reconstructions of each cranium. Cranial base angle was estimated by the angle between the sphenoidal and clival planes. The alisphenoid was evaluated qualitatively as the rostral portion of that bone separating orbit and middle cranial fossa. Finally, width of the presphenoid was evaluated as the width between the optic canals, inferior to the orbitosphenoid (lesser wings).Our results indicate that the sphenoid is highly variable in structure among the primate taxa under study. In all cases, the intrasphenoidal synchondrosis between the presphenoid and the basisphenoid remained patent. In many cases, the alisphenoid elements remained separate. We observed notable variation in the presphenoid, including length and width of the lesser wings. Despite the apparent variation, we did not find consistent evidence in support of our expectations based on phylogenetic signal. Cranial base angle did not differ between haplorhines and strepsirrhines, indicating that the influence of encephalization affects the cranial base postnatally. This is consistent with reports of increased brain growth in haplorhines in the postnatal period. We observed an expanded alisphenoid in haplorhines relative to some, but not all, of the strepsirrhines. Notably, the strepsirrhine Otolemur showed alisphenoid expansion rostral to the poles of the temporal lobes. Finally, we found a relatively wide presphenoid in many, but not all, of the strepsirrhines. The lesser wings of the presphenoid accommodated an enlarged olfactory fossa in all strepsirrhines, but the relative width of the presphenoid of Otolemur was within the range observed in haplorhines. Our results indicate that some of the sphenoidal traits that carry a phylogenetic signal in adults are present in many, but not all, neonate primates. These include width of the presphenoid and extent of the alisphenoid. In contrast, the effect of encephalization on cranial base angle occurs postnatally. In addition, it is apparent that factors independent of phylogeny influence the structure of the sphenoid in neonate primates.Support or Funding InformationNSF BCS‐1231717, NSF BCS‐1231350, NSF BCS‐0959438

Subject-specific multi-validation of a finite element model of ovine cervical functional spinal units

The complex motion and geometry of the spine in the cervical region makes it difficult to determine how loads are distributed through adjacent vertebrae or between the zygapophysial (facet) joints and the intervertebral disc. Validated finite element modes can give insight on this distribution. The aim of this contribution was to produce direct validation of subject-specific finite element models of Functional Spinal Units (FSU׳s) of the cervical spine and to evaluate the importance of including fibre directionality in the mechanical description of the annulus fibrosus.Eight specimens of cervical FSU׳s were prepared from five ovine spines and mechanically tested in axial compression monitoring overall load and displacements as well as local facet joints pressure and displacement. Subject-specific finite element models were produced from microCT image data reproducing the experimental setup and measuring global axial force and displacement as well as local facet joints displacement and contact forces. Material models and parameters were taken from the literature, testing isotropic and anisotropic materials for the annulus fibrosus.The validated models showed that adding the direction of the fibres to their non-linear behaviour in the description of the annulus fibrosus improves the predictions at large strain values but not at low strain values. The load transferred through the facet joints was always accurate, irrespective of the annulus material model, while the predicted facet displacement was larger than the measured one but not significantly. This is, to the authors׳ knowledge, the first subject-specific direct validation study on a group of specimens, accounting for inter-subject variability.

Effect of modeling parameters on the frequency response of the middle ear by means of finite element analysis.

A 3D finite element model of the human middle ear was developed for the investigation of the modeling parameters' effect on the frequency response. In this study, we incorporated realistic reconstructed geometries from microCT imaging data. The geometric representation of the stapedial annular ligament provided additional damping and the Rayleigh parameter β was adjusted to lower values in comparison to previous computational studies. The maximum displacement of the stapes footplate, equal to 0.168 μm, was observed at a frequency of 1050 Hz. The computational results were validated with experimental measurements. Good agreement is observed between our results and the experimental data and other finite element studies.

Voxel-based approach to generate entire human metacarpal bone with microscopic architecture for finite element analysis

With the development of micro-computed tomography (micro-CT) technology, it is possible to construct three-dimensional (3D) models of human bone without destruction of samples and predict mechanical behavior of bone using finite element analysis (FEA). However, due to large number of elements required for constructing the FE models of entire bone, this demands a substantial computational effort and the analysis usually needs a high level of computer. In this article, a voxel-based approach for generation of FE models of entire bone with microscopic architecture from micro-CT image data is proposed. To enable the FE analyses of entire bone to be run even on a general personal computer, grayscale intensity thresholds were adopted to reduce the amount of elements. Human metacarpal bone (MCP) bone was used as an example for demonstrating the applicability of the proposed method. The micro-CT images of the MCP bone were combined and converted into 3D array of pixels. Dual grayscale intensity threshold parameters were used to distinguish the pixels of bone tissues from those of surrounding soft tissues and improve predictive accuracy for the FE analyses with different sizes of elements. The method of selecting an appropriate value of the second grayscale intensity threshold was also suggested to minimize the area error for the reconstructed cross-sections of a FE structure. Experimental results showed that the entire FE MCP bone with microscopic architecture could be modeled and analyzed on a personal computer with reasonable accuracy.

Stress distribution on dentin-cement-post interface varying root canal and glass fiber post diameters. A three-dimensional finite element analysis based on micro-CT data

ObjectiveThe aim of the present study was to analyze the influence of root canal and glass fiber post diameters on the biomechanical behavior of the dentin/cement/post interface of a root-filled tooth using 3D finite element analysis. Material and MethodsSix models were built using micro-CT imaging data and SolidWorks 2007 software, varying the root canal (C) and the glass fiber post (P) diameters: C1P1-C=1 mm and P=1 mm; C2P1-C=2 mm and P=1 mm; C2P2-C=2 mm and P=2 mm; C3P1-C=3 mm and P=1 mm; C3P2-C=3 mm and P=2 mm; and C3P3-C=3 mm and P=3 mm. The numerical analysis was conducted with ANSYS Workbench 10.0. An oblique force (180 N at 45º) was applied to the palatal surface of the central incisor. The periodontal ligament surface was constrained on the three axes (x=y=z=0). Maximum principal stress (σmax) values were evaluated for the root dentin, cement layer, and glass fiber post. Results:The most evident stress was observed in the glass fiber post at C3P1 (323 MPa), and the maximum stress in the cement layer occurred at C1P1 (43.2 MPa). The stress on the root dentin was almost constant in all models with a peak in tension at C2P1 (64.5 MPa). ConclusionThe greatest discrepancy between root canal and post diameters is favorable for stress concentration at the post surface. The dentin remaining after the various root canal preparations did not increase the stress levels on the root.

Semi-automatic segmentation of subcutaneous tumours from micro-computed tomography images

This paper outlines the first attempt to segment the boundary of preclinical subcutaneous tumours, which are frequently used in cancer research, from micro-computed tomography (microCT) image data. MicroCT images provide low tissue contrast, and the tumour-to-muscle interface is hard to determine, however faint features exist which enable the boundary to be located. These are used as the basis of our semi-automatic segmentation algorithm. Local phase feature detection is used to highlight the faint boundary features, and a level set-based active contour is used to generate smooth contours that fit the sparse boundary features. The algorithm is validated against manually drawn contours and micro-positron emission tomography (microPET) images. When compared against manual expert segmentations, it was consistently able to segment at least 70% of the tumour region (n = 39) in both easy and difficult cases, and over a broad range of tumour volumes. When compared against tumour microPET data, it was able to capture over 80% of the functional microPET volume. Based on these results, we demonstrate the feasibility of subcutaneous tumour segmentation from microCT image data without the assistance of exogenous contrast agents. Our approach is a proof-of-concept that can be used as the foundation for further research, and to facilitate this, the code is open-source and available from www.setuvo.com.