Towards clinical-dose grating interferometry breast CT with fused intensity-based iterative reconstruction.

X-ray grating interferometry CT (GI-CT) is an emerging imaging modality which provides three complementary contrasts that could increase the diagnostic content of clinical breast CT: absorption, phase, and dark-field. Yet, reconstructing the three image channels under clinically compatible conditions is challenging because of severe ill-conditioning of the tomographic reconstruction problem. In this work we propose to solve this problem with a novel reconstruction algorithm that assumes a fixed relation between the absorption and the phase-contrast channel to reconstruct a single image by automatically fusing the absorption and phase channels. The results on both simulations and real data show that, enabled by the proposed algorithm, GI-CT outperforms conventional CT at a clinical dose.

Microstructural volumetric analysis of lateral ridge augmentation using differently conditioned tooth roots.

OBJECTIVES: Previous research revealed that autogenous tooth roots may be biologically equivalent to conventional bone grafts for lateral ridge augmentation. However, these analyses were limited to two dimensions, whereas healing is a volumetric process. The present study aimed at volumetrically assessing the microstructure following lateral ridge augmentation using extracted tooth roots. MATERIAL AND METHODS: The roots of differently conditioned maxillary premolars (i.e., healthy: PM-C; endodontically treated: PM-E; ligature-induced periodontitis: PM-P) and retromolar cortical autogenous bone (AB) blocks were used for lateral ridge augmentation at chronic-type defects in the lower quadrants of n = 16 foxhounds. At 12 weeks, titanium implants were inserted and left to heal for another 3 weeks. Tissue biopsies were scanned using microcomputed tomography (µCT), and volumes of interest were separated at the buccal and oral aspects to measure bone volume per tissue volume (BV/TV), trabecular thickness (Tb.Th), trabecular separation (Tb.Sp), and connectivity density (Conn.D). RESULTS: All groups investigated revealed comparable BV/TV, Tb.Th, Tb.Sp, and Conn.D values at either the augmented buccal or pristine oral aspects, respectively. A gradual but heterogeneous replacement of grafts was observed in all groups, but residual PM fragments were particularly noted in PM-C and PM-P groups. CONCLUSIONS: Differently conditioned PM and AB grafts were associated with a comparable bone microstructure within the grafted area. The duration of replacement resorption may vary considerably among the subjects. CLINICAL RELEVANCE: Autogenous tooth roots may serve as potential alternative to AB for localized alveolar ridge augmentation.

Three-dimensional assessment of crestal bone levels at titanium implants with different abutment microstructures and insertion depths using micro-computed tomography.

OBJECTIVES: To (i) assess the impact of insertion depth and abutment microstructure on the three-dimensional crestal bone-level changes at endosseous titanium implant using µCT and computerized image processing and (ii) to correlate the findings with previously reported histology. MATERIAL & METHODS: Titanium implants (conical abutment connection) were inserted in each hemimandible of n = 6 foxhounds with the implant shoulder (IS) located either in epicrestal (0 mm), supracrestal (+1 mm) or subcrestal (-1 mm) positions and randomly (split-mouth design) connected with machined or partially micro-grooved healing abutments. At 20 weeks, the tissue biopsies were processed for µCT and histological (HI) analyses. The volumetric dehiscence profile around the implants was computed as distance between the implant shoulder (IS) and the most coronal bone-to-implant contact (CBI) using MATLAB. The respective buccal and oral values were averaged, and agreement with the respective IS-CBI scores from HI was assessed using Bland-Altman plots. RESULTS: A median net bone gain was observed for supracrestal insertion depths at both abutment types, but lower bounds of the 75% quartile experienced net bone losses. Epicrestal and subcrestal insertion depths were linked to slight bone losses, and the buccal and oral dehiscences were smaller compared to supracrestal positioning. Bland-Altman plots yielded a moderate agreement of IS-CBI values measured with µCT and HI. CONCLUSION: The novel image processing method allowed reliable evaluations and pointed to a direct impact of insertion depths on crestal bone-level changes. Additionally, it demonstrated that HI morphometry crucially depends on the chosen cutting position.

Data-Driven Gradient Regularization for Quasi-Newton Optimization in Iterative Grating Interferometry CT Reconstruction.

Grating interferometry CT (GI-CT) is a promising technology that could play an important role in future breast cancer imaging. Thanks to its sensitivity to refraction and small-angle scattering, GI-CT could augment the diagnostic content of conventional absorption-based CT. However, reconstructing GI-CT tomographies is a complex task because of ill problem conditioning and high noise amplitudes. It has previously been shown that combining data-driven regularization with iterative reconstruction is promising for tackling challenging inverse problems in medical imaging. In this work, we present an algorithm that allows seamless combination of data-driven regularization with quasi-Newton solvers, which can better deal with ill-conditioned problems compared to gradient descent-based optimization algorithms. Contrary to most available algorithms, our method applies regularization in the gradient domain rather than in the image domain. This comes with a crucial advantage when applied in conjunction with quasi-Newton solvers: the Hessian is approximated solely based on denoised data. We apply the proposed method, which we call GradReg, to both conventional breast CT and GI-CT and show that both significantly benefit from our approach in terms of dose efficiency. Moreover, our results suggest that thanks to its sharper gradients that carry more high spatial-frequency content, GI-CT can benefit more from GradReg compared to conventional breast CT. Crucially, GradReg can be applied to any image reconstruction task which relies on gradient-based updates.

Analysis of the Morpho-Geometrical Changes of the Root Canal System Produced by TF Adaptive vs. BioRace: A Micro-Computed Tomography Study.

We aimed to analyze the morpho-geometric changes of the root canal system created by two rotary systems (TF Adaptive and BioRace) using micro-CT technology. Two concepts of rotary file system kinematics, continuous rotation and adaptive kinematics, were used in root canal preparation. Twenty mandibular molars (n = 20) were selected with the following criteria: the teeth have mesial roots with a single and continuous isthmus connecting the mesiobuccal and mesiolingual canals (Vertucci's Type I configuration) and distal roots with independent canals. Teeth were scanned at a resolution of 14 µm. Canals were divided equally into two groups and then enlarged sequentially using the BioRace system and TF Adaptive system according to manufacturer protocol. Co-registered images, before and after preparation, were evaluated for morphometric measurements of canal surface area, volume, structure model index, thickness, straightening, and un-instrumented surface area. Before and after preparation, data were statistically analyzed using a paired sample t-test. After preparation, data were analyzed using an unpaired sample test. The preparation by both systems significantly changed canal surface area, volume, structure model index, and thickness in both systems. There were no significant differences between instrument types with respect to these parameters (p > 0.05). TF Adaptive was associated with less straightening (8% compared with 17% for BioRace in the mesial canal, p > 0.05). Both instrumentation systems produced canal preparations with adequate geometrical changes. BioRace straightened the mesial canals more than TF Adaptive.

Micro-cleanliness of Hard Tissue Debris After Advanced Irrigation and Comparison Between EndoVac and XP-endo Finisher: A Microcomputed Tomographic Study.

INTRODUCTION: Conventional irrigation techniques do not remove debris adequately. The remaining tissue debris cause infection inside the root canal and may also affect the seal of the root canal. The study aimed to compare the ability of EndoVac (EV) with XP-endo finisher (XPF) in debris removal using micro-CT analysis. MATERIALS AND METHODS: We used 12 lower first permanent molar human teeth for this study. The root canals were instrumented using a small TF adaptive system. Then, the volume of debris was calculated. Teeth were divided into two groups, according to advanced irrigation methods, with six teeth per group: EV group and XPF group. The volume of debris was calculated again. The paired-sample t-test was used to compare the volume of the debris before and after the use of advanced irrigation methods with the statistical significance of P < 0.05. The percentage of debris reduction was also calculated. RESULTS: Both EV and XPF showed a significant decrease of debris in the mesial canals (P < 0.05), whereas EV only showed a significant reduction of debris in the distal canals. CONCLUSION: Both EV and XPF were able to significantly reduce debris after instrumentation in the mesial canals of lower first mandibular molars. CLINICAL SIGNIFICANCE: The study provides insight into the recent advanced methods used in debris removal and canal disinfection.

Micro-computed tomography: a method for the non-destructive evaluation of the three-dimensional structure of biological specimens.

The large increase in interest in micro-computed tomography (micro-CT) over the last decade reflects the+ need for a method able to non-destructively visualize the internal three-dimensional structure of an object. Thereby, the real beauty of computed tomography lies in the fact that it is available for a large range of nominal resolutions, which allows hierarchical imaging from whole bodies down to the tissue level. Although micro-CT is currently mainly used for imaging of hard tissue (i.e., bone and tooth), future developments might also allow high soft tissue contrast either using appropriate contrast agents or x-ray contrast mechanisms. This chapter aims to review the steps necessary for a successful micro-CT measurement. Although the actual measurement is often machine dependent, the chapter does not describe a specific system but rather lists all steps that eventually have to be considered to set up a measurement, run the measurement, process the image data, and get morphometric indices as a result. The chapter provides an easy understandable manual that should allow newcomers to perform successful measurements and hence to best profit from this powerful technique.

Patient-specific estimation of detailed cochlear shape from clinical CT images.

PURPOSE: A personalized estimation of the cochlear shape can be used to create computational anatomical models to aid cochlear implant (CI) surgery and CI audio processor programming ultimately resulting in improved hearing restoration. The purpose of this work is to develop and test a method for estimation of the detailed patient-specific cochlear shape from CT images. METHODS: From a collection of temporal bone [Formula: see text]CT images, we build a cochlear statistical deformation model (SDM), which is a description of how a human cochlea deforms to represent the observed anatomical variability. The model is used for regularization of a non-rigid image registration procedure between a patient CT scan and a [Formula: see text]CT image, allowing us to estimate the detailed patient-specific cochlear shape. RESULTS: We test the accuracy and precision of the predicted cochlear shape using both [Formula: see text]CT and CT images. The evaluation is based on classic generic metrics, where we achieve competitive accuracy with the state-of-the-art methods for the task. Additionally, we expand the evaluation with a few anatomically specific scores. CONCLUSIONS: The paper presents the process of building and using the SDM of the cochlea. Compared to current best practice, we demonstrate competitive performance and some useful properties of our method.

Ultrastructural properties in cortical bone vary greatly in two inbred strains of mice as assessed by synchrotron light based micro- and nano-CT.

UNLABELLED: Nondestructive SR-based microCT and nano-CT methods have been designed for 3D quantification and morphometric analysis of ultrastructural phenotypes within murine cortical bone, namely the canal network and the osteocyte lacunar system. Results in two different mouse strains, C57BL/6J-Ghrhr(lit)/J and C3.B6-Ghrhr(lit)/J, showed that the cannular and lacunar morphometry and their bone mechanics were fundamentally different. INTRODUCTION: To describe the different aspects of bone quality, we followed a hierarchical approach and assessed bone tissue properties in different regimens of spatial resolution, beginning at the organ level and going down to cellular dimensions. For these purposes, we developed different synchrotron radiation (SR)-based CT methods to assess ultrastructural phenotypes of murine bone. MATERIALS AND METHODS: The femoral mid-diaphyses of 12 C57BL/6J-Ghrhr(lit)/J (B6-lit/lit) and 12 homozygous mutants C3.B6-Ghrhr(lit)/J (C3.B6-lit/lit) were measured with global SR microCT and local SR nano-CT (nCT) at nominal resolutions ranging from 3.5 microm to 700 nm, respectively. For volumetric quantification, morphometric indices were determined for the cortical bone, the canal network, and the osteocyte lacunar system using negative imaging. Moreover, the biomechanics of B6-lit/lit and C3.B6-lit/lit mice was determined by three-point bending. RESULTS: The femoral mid-diaphysis of C3.B6-lit/lit was larger compared with B6-lit/lit mice. On an ultrastructural level, the cannular indices for C3.B6-lit/lit were generally bigger in comparison with B6-lit/lit mice. Accordingly, we derived and showed a scaling rule, saying that overall cannular indices scaled with bone size, whereas indices describing basic elements of cannular and lacunar morphometry did not. Although in C3.B6-lit/lit, the mean canal volume was larger than in B6-lit/lit, canal number density was proportionally smaller in C3.B6-lit/lit, so that lacuna volume density was found to be constant and therefore independent of mouse strain and sex. The mechanical properties in C3.B6-lit/lit were generally improved compared with B6-lit/lit specimens. For C3.B6-lit/lit, we observed a sex specificity of the mechanical parameters, which could not be explained by bone morphometry on an organ level. However, there is evidence that for C3.B6-lit/lit, the larger cortical bone mass is counterbalanced or even outweighed by the larger canal network in the female mice. CONCLUSIONS: We established a strategy to subdivide murine intracortical porosity into ultrastructural phenotypes, namely the canal network and the osteocyte lacunar system. Nondestructive global and local SR-based CT methods have been designed for 3D quantification and subsequent morphometric analysis of these phenotypes. Results in the two different mouse strains C57BL/6J-Ghrhr(lit)/J and C3.B6-Ghrhr(lit)/J showed that the cannular and lacunar morphometry and the biomechanical properties were fundamentally different.

Automated compartmental analysis for high-throughput skeletal phenotyping in femora of genetic mouse models.

Mouse models are widely used in genomic studies for quantitative trait loci (QTL) analyses. In the field of skeletal micro-structure, microCT has proven to be an invaluable imaging tool for the characterization of structural bone traits. However, the definition of analysis compartments requires a lot of user interaction, and therefore is not applicable as a standard way to analyze genetic linkage studies with several hundreds of animals. Here, we developed an automated three-dimensional based algorithm for a high-throughput regional analysis of three compartments in murine femora, including whole bone, cortical bone in the diaphysis and trabecular bone in the metaphysis. The algorithm relies on basic image processing concepts using morphological operators as well as a new approach of separating cortical from trabecular bone. Reproducibility of the automatic approach was investigated with respect to precision errors (PE(%CV)) of micro-structural indices analyzed in these automatically defined compartments. The developed algorithm was then used to perform a high-throughput analysis of over 2000 femora in a genetic linkage study for further examination of stability and performance. Precision errors were 3.5% or less for all micro-structural indices. The analysis of one femur (mask generation and parameter evaluation) took 7 min on an AlphaServer DS25. The algorithm showed a very high reliability and worked successfully for 99.64% of all femora. Investigations of correlations amongst the assessed micro-structural indices together with heritability and polygene estimates revealed apparent volume density (AVD), trabecular thickness (Tb.Th), trabecular separation (Tb.Sp) and cortical thickness (Ct.Th) as candidates for a successful QTL analysis. The presented automatic analysis allows for standardized high-throughput phenotypic screening in mice femora for large genetic linkage studies with very high reliability and good precision.

A sensitivity analysis of the volumetric spatial decomposition algorithm.

Recently, we proposed a new computational approach for the volumetric spatial decomposition of a three-dimensional bone structure into its basic rod and plate elements. This method was based on an image skeletonization approach, where two model parameters were used to identify an ideal skeleton. The goal of this study was to estimate the sensitivity of local morphometric indices to these two model parameters. Our results showed that the rod derived indices behaved more smoothly than plate derived indices, which suggests that rod derived indices are more trustworthy. The results also demonstrated that it was reasonable to reduce the model to only one parameter by setting the noise parameter n to twice the value of the slenderness parameter s. In conclusion, we found that local morphometric indices are reliable measures showing large differences between samples and thus may shed new light on structural differences of trabecular bone in a local fashion by adequately choosing one single optimization parameter.

Automatic registration of 2D histological sections to 3D microCT volumes: Trabecular bone.

Histomorphometry and microCT are the two dominant imaging techniques to study bone structure and quality to evaluate repair, regeneration, and disease. These two methods are complementary; where histology provides highly resolved tissue properties on a cellular level in 2D, microCT provides spatial information of bone micro-structure in 3D. For this reason, both of these modalities are commonly used in bone studies. As it is not trivial to combine the images of these two modalities, the two methods are typically applied to different specimens within a study. However, we believe that applying both imaging modalities to the same specimen with a suitable fusion strategy may further strengthen the value of each modality. Therefore, we propose a registration method to align 2D histology slices with a 3D microCT volume, without any prior knowledge of the sectioning direction. In a preprocessing step, bone is extracted from both images. Then, we use a strategy for initializing potential locations, and an iterative approach for searching for an ideal fitting plane using Radon-based rigid transforms and feature-based affine alignments. The algorithm was tested and validated with simulated and real data. For the latter, microCT images of trabecular bone with 76 corresponding histological sections acquired from decalcified and calcified specimens were used. The registration resulted in 94.7% acceptable solutions as defined by a registration orientation error of less than 3°. Average registration accuracy of the acceptable results was 0.6°, leading to a target registration error for our method of 106.3µm, computed based on landmarks annotated by an observer. This corresponds roughly to 10pixels in the images; although, the relation to actual visible structures that provide the features to register, is arguably more relevant.

Fast estimation of Colles' fracture load of the distal section of the radius by homogenized finite element analysis based on HR-pQCT.

Fractures of the distal section of the radius (Colles' fractures) occur earlier in life than other osteoporotic fractures. Therefore, they can be interpreted as a warning signal for later, more deleterious fractures of vertebral bodies or the femoral neck. In the past decade, the advent of HR-pQCT allowed a detailed architectural analysis of the distal radius and an automated but time-consuming estimation of its strength with linear micro-finite element (µFE) analysis. Recently, a second generation of HR-pQCT scanner (XtremeCT II, SCANCO Medical, Switzerland) with a resolution beyond 61 µm became available for even more refined biomechanical investigations in vivo. This raises the question how biomechanical outcome variables compare between the original (LR) and the new (HR) scanner resolution. Accordingly, the aim of this work was to validate experimentally a patient-specific homogenized finite element (hFE) analysis of the distal section of the human radius for the fast prediction of Colles' fracture load based on the last generation HR-pQCT. Fourteen pairs of fresh frozen forearms (mean age = 77.5±9) were scanned intact using the high (61 µm) and the low (82 µm) resolution protocols that correspond to the new and original HR-pQCT systems. From each forearm, the 20mm most distal section of the radius were dissected out, scanned with µCT at 16.4 µm and tested experimentally under compression up to failure for assessment of stiffness and ultimate load. Linear and nonlinear hFE models together with linear micro finite element (µFE) models were then generated based on the µCT and HR-pQCT reconstructions to predict the aforementioned mechanical properties of 24 sections. Precision errors of the short term reproducibility of the FE analyses were measured based on the repeated scans of 12 sections. The calculated failure loads correlated strongly with those measured in the experiments: accounting for donor as a random factor, the nonlinear hFE provided a marginal coefficient of determination (Rm2) of 0.957 for the high resolution (HR) and 0.948 for the low resolution (LR) protocols, the linear hFE with Rm2 of 0.957 for the HR and 0.947 for the LR protocols. Linear µFE predictions of the ultimate load were similar with an Rm2 of 0.950 for the HR and 0.954 for the LR protocols, respectively. Nonlinear hFE strength computation led to precision errors of 2.2 and 2.3% which were higher than the ones calculated based on the linear hFE (1.6 and 1.9%) and linear µFE (1.2 and 1.6%) for the HR and LR protocols respectively. Computation of the fracture load with nonlinear hFE demanded in average 6h of CPU time which was 3 times faster than with linear µFE, while computation with linear hFE took only a few minutes. This study delivers an extensive experimental and numerical validation for the application of an accurate and fast hFE diagnostic tool to help in identifying individuals who may be at risk of an osteoporotic wrist fracture and to follow up pharmacological and other treatments in such patients.

A multiscale imaging and modelling dataset of the human inner ear.

Understanding the human inner ear anatomy and its internal structures is paramount to advance hearing implant technology. While the emergence of imaging devices allowed researchers to improve understanding of intracochlear structures, the difficulties to collect appropriate data has resulted in studies conducted with few samples. To assist the cochlear research community, a large collection of human temporal bone images is being made available. This data descriptor, therefore, describes a rich set of image volumes acquired using cone beam computed tomography and micro-CT modalities, accompanied by manual delineations of the cochlea and sub-compartments, a statistical shape model encoding its anatomical variability, and data for electrode insertion and electrical simulations. This data makes an important asset for future studies in need of high-resolution data and related statistical data objects of the cochlea used to leverage scientific hypotheses. It is of relevance to anatomists, audiologists, computer scientists in the different domains of image analysis, computer simulations, imaging formation, and for biomedical engineers designing new strategies for cochlear implantations, electrode design, and others.

Importance of individual rods and plates in the assessment of bone quality and their contribution to bone stiffness.

UNLABELLED: Local morphometry based on the assessment of individual rods and plates was applied to 42 human vertebral trabecular bone samples. Results showed that multiple linear regression models based on local morphometry as a measure for bone microstructure helped improving our understanding of the role of local structural changes in the determination of bone stiffness as assessed from direct and computational biomechanics. INTRODUCTION: In a recent study, we proposed a method for local morphometry of trabecular bone, i.e., morphometry as applied to individual rods and plates. In this study, we used this method to study the relative importance of local morphometry in the assessment of bone architecture and its relative contribution to the stiffness of human vertebral bone. MATERIALS AND METHODS: We extracted 42 human trabecular bone autopsies from nine intact spinal columns. The cylindrical samples were imaged with muCT to assess bone microstructure. From these images, global and local morphometric indices were derived and related to Young's modulus as assessed by experimental uniaxial compression testing (Emeas) and computational finite element analysis (EFE). RESULTS: We found the best single predictor for Young's modulus to be apparent bone volume density (BV/TV), which explained 89% of the variance in EFE when fitted with a power law. A multiple linear regression model combining mean trabecular spacing (Tb.Sp), mean slenderness of the rods (), and the relative amount of rod volume to total bone volume (Ro.BV/BV) was able to explain 90% of the variance in EFE. This model could not be improved by adding BV/TV as an independent variable. Furthermore, we found that mean trabecular thickness of the rods was significantly related to EFE (r2 = 0.42), whereas mean trabecular thickness of plates had no correlation to Young's modulus. Because the globally determined trabecular thickness does not discriminate between rods and plates, this index had only a poor predictive power for EFE (r2 = 0.09), showing the importance of local analysis of individual rods and plates. CONCLUSIONS: From these results, we conclude that models based on local morphometry help improving our understanding of the relative importance of local structural changes in the determination of the stiffness of bone. Separate analysis of individual rods and plates may help to better predict age and disease-related fractures as well as to shed new light on the effect of pharmaceutical intervention in the prevention of such fractures beyond BMD.

Volumetric spatial decomposition of trabecular bone into rods and plates--a new method for local bone morphometry.

Bone microarchitecture is believed to play a key role in determining bone quality. We therefore present a new method for the volumetric spatial decomposition of trabecular bone samples into its basic elements (rods and plates). This new method is a framework for the element based description of bone microarchitecture. First, the newly developed algorithm was validated on computer-generated models. Then, it was applied to 328 human trabecular bone samples harvested from 70 donors at five different anatomical sites (calcaneus, femoral head, iliac crest, lumbar spine 2 and 4), which were previously scanned by microcomputed tomography. Standard three-dimensional morphometric algorithms were used to analyze the trabeculae on an individual basis with respect to their volume, surface, and thickness. The results were statistically compared for the five sites. In this study, it was possible for the first time to spatially decompose trabecular bone structures in its volumetric elements; rods and plates. The size of the largest element in the structures showed significant differences for the five compared sites. In samples from femoral head, we found that basically one "major element" was spanning through the whole structure whereas in lumbar spine and calcaneus, smaller elements dominate. From this, we suggest that the strength of strong, dense plate-like structures is determined by the major elements whereas in looser rod-like structures the strength is given by the arrangement, quality, and shape of a whole set of elements. Furthermore, we found that globally determined structural indices such as the mean curvature of the bone surface () or related to this the structure model index (SMI) are almost exclusively explained by the arrangement of the plates. This also suggests that rods hold independent information characterizing trabecular bone quality, especially in the spine. These findings may improve the understanding of the site-specific role of bone microarchitecture in determining bone quality and in future studies the competence of bone.

The interaction of microstructure and volume fraction in predicting failure in cancellous bone.

Inroads have been made in the diagnosis and treatment of osteoporosis, yet dual-energy X-ray absorptiometry is still the primary diagnostic modality. This method provides 2D projections of an irregular 3D construct. However, human cancellous bone is highly heterogeneous with varying material properties. Therefore, to properly assess fracture risk, it is imperative to take into consideration microstructural indices besides subregional bone volume fraction (BV/TV). A power law model with average BV/TV as the independent variable describes 38% of the variation in yield strength; however, this predictive power is increased to 56% when BV/TV of the weakest subregion is considered. Of twenty-five specimens studied, 76% had minimum BV/TV, maximum principal Eigen value of the fabric tensor (H1) and minimum connectivity density (Conn.D) values within the visually determined failure regions. These three independent morphometric indices yielded significant differences between the failure and non-failure regions of each specimen. From the results, we conclude that subregions with minimal BV/TV values are better predictors of mechanical failure in cancellous bone than average specimen BV/TV. Addition of microstructural indices augments this predictive power to generate a trabecular failure prediction model based on volume fraction and cancellous bone microstructure specifically in areas where trabecular failure is most likely to occur.

Micro-CT vs. Whole Body Multirow Detector CT for Analysing Bone Regeneration in an Animal Model.

OBJECTIVES: Compared with multirow detector CT (MDCT), specimen (ex vivo) micro-CT (µCT) has a significantly higher (~ 30 x) spatial resolution and is considered the gold standard for assessing bone above the cellular level. However, it is expensive and time-consuming, and when applied in vivo, the radiation dose accumulates considerably. The aim of this study was to examine whether the lower resolution of the widely used MDCT is sufficient to qualitatively and quantitatively evaluate bone regeneration in rats. METHODS: Forty critical-size defects (5mm) were placed in the mandibular angle of rats and covered with coated bioactive titanium implants to promote bone healing. Five time points were selected (7, 14, 28, 56 and 112 days). µCT and MDCT were used to evaluate the defect region to determine the bone volume (BV), tissue mineral density (TMD) and bone mineral content (BMC). RESULTS: MDCT constantly achieved higher BV values than µCT (10.73±7.84 mm3 vs. 6.62±4.96 mm3, p<0.0001) and consistently lower TMD values (547.68±163.83 mm3 vs. 876.18±121.21 mm3, p<0.0001). No relevant difference was obtained for BMC (6.48±5.71 mm3 vs. 6.15±5.21 mm3, p = 0.40). BV and BMC showed very strong correlations between both methods, whereas TMD was only moderately correlated (r = 0.87, r = 0.90, r = 0.68, p < 0.0001). CONCLUSIONS: Due to partial volume effects, MDCT overestimated BV and underestimated TMD but accurately determined BMC, even in small volumes, compared with µCT. Therefore, if bone quantity is a sufficient end point, a considerable number of animals and costs can be saved, and compared with in vivo µCT, the required dose of radiation can be reduced.

Design and implementation of a novel mechanical testing system for cellular solids.

Cellular solids constitute an important class of engineering materials encompassing both man-made and natural constructs. Materials such as wood, cork, coral, and cancellous bone are examples of cellular solids. The structural analysis of cellular solid failure has been limited to 2D sections to illustrate global fracture patterns. Due to the inherent destructiveness of 2D methods, dynamic assessment of fracture progression has not been possible. Image-guided failure assessment (IGFA), a noninvasive technique to analyze 3D progressive bone failure, has been developed utilizing stepwise microcompression in combination with time-lapsed microcomputed tomographic imaging (microCT). This method allows for the assessment of fracture progression in the plastic region, where much of the structural deformation/energy absorption is encountered in a cellular solid. Therefore, the goal of this project was to design and fabricate a novel micromechanical testing system to validate the effectiveness of the stepwise IGFA technique compared to classical continuous mechanical testing, using a variety of engineered and natural cellular solids. In our analysis, we found stepwise compression to be a valid approach for IGFA with high precision and accuracy comparable to classical continuous testing. Therefore, this approach complements the conventional mechanical testing methods by providing visual insight into the failure propagation mechanisms of cellular solids.

Automated 3D-2D registration of X-ray microcomputed tomography with histological sections for dental implants in bone using chamfer matching and simulated annealing.

We propose a novel 3D-2D registration approach for micro-computed tomography (µCT) and histology (HI), constructed for dental implant biopsies, that finds the position and normal vector of the oblique slice from µCT that corresponds to HI. During image pre-processing, the implants and the bone tissue are segmented using a combination of thresholding, morphological filters and component labeling. After this, chamfer matching is employed to register the implant edges and fine registration of the bone tissues is achieved using simulated annealing. The method was tested on n=10 biopsies, obtained at 20 weeks after non-submerged healing in the canine mandible. The specimens were scanned with µCT 100 and processed for hard tissue sectioning. After registration, we assessed the agreement of bone to implant contact (BIC) using automated and manual measurements. Statistical analysis was conducted to test the agreement of the BIC measurements in the registered samples. Registration was successful for all specimens and agreement of the respective binary images was high (median: 0.90, 1.-3. Qu.: 0.89-0.91). Direct comparison of BIC yielded that automated (median 0.82, 1.-3. Qu.: 0.75-0.85) and manual (median 0.61, 1.-3. Qu.: 0.52-0.67) measures from µCT were significant positively correlated with HI (median 0.65, 1.-3. Qu.: 0.59-0.72) between µCT and HI groups (manual: R(2)=0.87, automated: R(2)=0.75, p<0.001). The results show that this method yields promising results and that µCT may become a valid alternative to assess osseointegration in three dimensions.