Micro CT analysis of the subarticular bone structure in the area of the talar trochlea

Purpose: Certain regions of the talar trochlea are recognized as exhibiting varying cartilage thickness and degrees of subchondral bone mineralization. These changes have been attributed to the long-term loading history. For the current study, we accepted the hypothesis that stress-induced alterations of the joint surface include not only varying degrees of subchondral lamellar mineralization, but also structural changes of the subarticular cancellous bone. Methods: In order to examine the structure of the subarticular cancellous bone, ten formalin-fixed talar trochleae were analyzed using micro CT. Sixteen measurement zones were defined and then evaluated in five layers each of 1-mm thickness, enabling assessment of the cancellous architecture extending 5mm below the trochlear surface using numerical and structural parameters. Results: As with mineralization patterns in the subchondral lamella, large variation was observed regarding bone volume, trabecular quantity, thickness, and spacing, as well as for structure model index and degree of anisotropy, depending on localization. In addition, like previous reports examining mineralization of the subchondral lamella, two distinct groups could be identified as "bicentric” or "monocentric”. Conclusions: These results show that structural tissue adaptation probably due to loading history is also evident within the subarticular cancellous bon

X-ray micro computed tomography for the visualization of an atherosclerotic human coronary artery

Atherosclerosis refers to narrowing or blocking of blood vessels that can lead to a heart attack, chest pain or stroke. Constricted segments of diseased arteries exhibit considerably increased wall shear stress, compared to the healthy ones. One of the possibilities to improve patient's treatment is the application of nano-therapeutic approaches, based on shear stress sensitive nano-containers. In order to tailor the chemical composition and subsequent physical properties of such liposomes, one has to know precisely the morphology of critically stenosed arteries at micrometre resolution. It is often obtained by means of histology, which has the drawback of offering only two-dimensional information. Additionally, it requires the artery to be decalcified before sectioning, which might lead to deformations within the tissue. Micro computed tomography (muCT) enables the three-dimensional (3D) visualization of soft and hard tissues at micrometre level. muCT allows lumen segmentation that is crucial for subsequent flow simulation analysis. In this communication, tomographic images of a human coronary artery before and after decalcification are qualitatively and quantitatively compared. We analyse the cross section of the diseased human coronary artery before and after decalcification, and calculate the lumen area of both samples

Comparative analysis of bone structural parameters reveals subchondral cortical plate resorption and increased trabecular bone remodeling in human facet joint osteoarthritis

Facet joint osteoarthritis is a prominent feature of degenerative spine disorders, highly prevalent in ageing populations, and considered a major cause for chronic lower back pain. Since there is no targeted pharmacological therapy, clinical management of disease includes analgesic or surgical treatment. The specific cellular, molecular, and structural changes underpinning facet joint osteoarthritis remain largely elusive. The aim of this study was to determine osteoarthritis-related structural alterations in cortical and trabecular subchondral bone compartments. To this end, we conducted comparative micro computed tomography analysis in healthy (n = 15) and osteoarthritic (n = 22) lumbar facet joints. In osteoarthritic joints, subchondral cortical plate thickness and porosity were significantly reduced. The trabecular compartment displayed a 42 percent increase in bone volume fraction due to an increase in trabecular number, but not trabecular thickness. Bone structural alterations were associated with radiological osteoarthritis severity, mildly age-dependent but not gender-dependent. There was a lack of association between structural parameters of cortical and trabecular compartments in healthy and osteoarthritic specimens. The specific structural alterations suggest elevated subchondral bone resorption and turnover as a potential treatment target in facet joint osteoarthritis

Microscale stress-geometry interactions in an additively manufactured NiTi cardiovascular stent: A synchrotron dual imaging tomography and diffraction study

This study explores cardiovascular stents fabricated using laser powder bed fusion (LPBF); an emerging method to offer patient-specific customisable parts. Here, the shape memory alloy NiTi, in a near equiatomic composition, was investigated to deconvolve the material response from macroscopic component effects. Specifically, stress-geometry interactions were revealed, in-situ, for a minaturised cardiovascular stent subjected to an externally applied cylindrical stress whilst acquiring synchrotron X-ray imaging and diffraction data. The approach enabled the collection of spatially resolved micromechanical deformation data; the formation of stress-induced martensite and R-phase was evident, occurring in locations near junctions between stent ligaments where stress concentrations exist. In the as-fabricated condition, hardness maps were obtained through nanoindentation, demonstrating that the localised deformation and deformation patterning is further controlled by porosity and microstructural heterogeneity. Electron backscatter diffraction (EBSD) supported these observations, showing a finer grain structure near stent junctions with higher associated lattice curvature. These features, combined with stress concentrations when loaded will initiate localised phase transformations. If the stent was subjected to repeated loading, representing in-vivo conditions, these regions would be susceptible to cyclic damage through transformation memory loss, leading to premature component failure. This study highlights the challenges that must be addressed for the post-processing treatment of LABF-processed stents for healthcare-related applications

The DIAD Approach to Correlative Synchrotron X‑ray Imaging and Diffraction Analysis of Human Enamel

The Dual Imaging and Diffraction (DIAD) beamline at Diamond Light Source (Didcot, U.K.) implements a correlative approach to the dynamic study of materials based on concurrent analysis of identical sample locations using complementary X-ray modalities to reveal structural detail at various length scales. Namely, the underlying beamline principle and its practical implementation allow the collocation of chosen regions within the sample and their interrogation using real-space imaging (radiography and tomography) and reciprocal space scattering (diffraction). The switching between the two principal modes is made smooth and rapid by design, so that the data collected is interlaced to obtain near-simultaneous multimodal characterization. Different specific photon energies are used for each mode, and the interlacing of acquisition steps allows conducting static and dynamic experiments. Building on the demonstrated realization of this state-of-the-art approach requires further refining of the experimental practice, namely, the methods for gauge volume collocation under different modes of beam–sample interaction. To address this challenge, experiments were conducted at DIAD devoted to the study of human dental enamel, a hierarchical structure composed of hydroxyapatite mineral nanocrystals, as a static sample previously affected by dental caries (tooth decay) as well as under dynamic conditions simulating the process of acid demineralization. Collocation and correlation were achieved between WAXS (wide-angle X-ray scattering), 2D (radiographic), and 3D (tomographic) imaging. While X-ray imaging in 2D or 3D modes reveals real-space details of the sample microstructure, X-ray scattering data for each gauge volume provided statistical nanoscale and ultrastructural polycrystal reciprocal-space information such as phase and preferred orientation (texture). Careful registration of the gauge volume positions recorded during the scans allowed direct covisualization of the data from two modalities. Diffraction gauge volumes were identified and visualized within the tomographic data sets, revealing the underlying local information to support the interpretation of the diffraction patterns. The present implementation of the 4D microscopy paradigm allowed following the progression of demineralization and its correlation with time-dependent WAXS pattern evolution in an approach that is transferable to other material systems

Micro- and nanostructure of human teeth : a synchrotron radiation-based X-ray study

The anisotropic composite nature of human teeth guarantees their function for decades under high mechanical loads and adverse chemical conditions. Even more so since only marginal remodelling and repair mechanisms take place in adult teeth. While the macroscopical anatomy of the tooth has been well understood, long range ordering of the tooth’s micro and nano components is still matter of research. Tooth micro- and nanostructure has been extensively studied, mainly with two-dimensional approaches as, for example, electron microscopy. The ultrastructural organization over a whole tooth is, however, not readily accessible with these approaches, because they only permit a very localized observation and often even remove the investigated structures from their natural three-dimensional organization. The high degree of anisotropy in both dentin and enamel on the micro- and nanometer scale has a strong impact on the tooth’s mechanical properties. For example, the Young’s modulus and crack resistance of dentin are different parallel and perpendicular to the dentin tubules. Synchrotron radiation-based micro computed tomography with pixel sizes in the sub-micrometer range allows to three-dimensionally image dentin tubules, however only over restricted specimen sizes below one millimetre in diameter. To map the tubular network over an entire tooth, multiple scans are necessary. Given the generally limited beamtime available at synchrotron sources, a method has to be identified that allows for the visualization of dentin tubules with high accuracy and within reasonable time. Single distance phase retrieval, multiple distance phase retrieval and absorption contrast datasets, acquired at the beamline ID 19 at ESRF, were compared concerning their spatial and density resolution as well as their suitability for tubule rendering, and single distance phase retrieval, with a specimen detector distance of 75% of the critical value d^2/lambda, was found to yield optimal results. The knowledge of tooth ultrastructure is of particular interest when dealing with carious lesions. The treatment of carious lesions is nowadays accompanied by the removal of affected hard tissues and their replacement with isotropic restoration materials. Despite their high performance, these restorations have limited life span. As a result, additional clinical interventions and the replacement of the restoration are often necessary. An alternative would be the fabrication of anisotropic fillings, which mimic the natural organization of the tooth. Such structures are speculated to exhibit properties similar to those of healthy teeth and thus to be superior to the isotropic materials currently in use, thus extending restoration lifetime. For this purpose an extensive mapping of tooth ultrastructure is necessary. Small-angle X-ray scattering (SAXS) in scanning setup allows for the investigation of tooth nanostructural organization over extended areas. Scanning SAXS measurements of micrometer-thin tooth slices were performed at the cSAXS beamline at the Paul Scherrer Institut, revealing a high degree of structural organization of the tooth’s nanometer-sized components. Based on this knowledge, a model for bio-mimetic fillings was proposed. Nonetheless, bio-inspired fillings would still require costly interventions, and their superior performance has not been demonstrated yet. As alternative to restorations, where the affected tissue is removed and replaced with man-made materials, a treatment based on the re-mineralization of the carious lesion could be performed. The aim is not only the re-mineralization of de-mineralized tissues, but also the re-establishment of tooth morphology including its nanostructure, which in return will ensure mechanical properties comparable to those of healthy tissue. The morphology of the carious tissue is crucial for this procedure, as the structures retained in the lesion can act as nucleation sites for the re-mineralizing crystallites. Carious dentin and enamel were examined with scanning SAXS to determine whether the organization on the nanometer level is retained to some extent. In dentin, a significant part of the collagen network is retained concerning orientation and abundance after mild demineralization has taken place. In enamel, the overall orientation of the hydroxyapatite crystallites is unaltered, despite the complex organization of enamel lesions, consisting of alternating layers of de- and re-mineralized tissue

Mineralization of Early Stage Carious Lesions In Vitro—A Quantitative Approach

Micro computed tomography has been combined with dedicated data analysis for the in vitro quantification of sub-surface enamel lesion mineralization. Two artificial white spot lesions, generated on a human molar crown in vitro, were examined. One lesion was treated with a self-assembling peptide intended to trigger nucleation of hydroxyapatite crystals. We non-destructively determined the local X-ray attenuation within the specimens before and after treatment. The three-dimensional data was rigidly registered. Three interpolation methods, i.e., nearest neighbor, tri-linear, and tri-cubic interpolation were evaluated. The mineralization of the affected regions was quantified via joint histogram analysis, i.e., a voxel-by-voxel comparison of the tomography data before and after mineralization. After ten days incubation, the mean mineralization coefficient reached 35.5% for the peptide-treated specimen compared to 11.5% for the control. This pilot study does not give any evidence for the efficacy of peptide treatment nor allows estimating the necessary number of specimens to achieve significance, but shows a sound methodological approach on the basis of the joint histogram analysis

Osteoarthritis alters the patellar bones subchondral trabecular architecture

Following the principles of "morphology reveals biomechanics," the cartilage-osseous interface and the trabecular network show defined adaptation in response to physiological loading. In the case of a compromised relationship, the ability to support the load diminishes and the onset of osteoarthritis (OA) may arise. To describe and quantify the changes within the subchondral bone plate (SBP) and trabecular architecture, 10 human OA patellae were investigated by CT and micro-CT. The results are presented in comparison to a previously published dataset of 10 non-OA patellae which were evaluated in the same manner. The analyzed OA samples showed no distinctive mineralization pattern in regards to the physiological biomechanics, but a highly irregular disseminated distribution. In addition, no regularity in bone distribution and architecture across the trabecular network was found. We observed a decrease of material as the bone volume and trabecular thickness/number were significantly reduced. In comparison to non-OA samples, greatest differences for all parameters were found within the first mm of trabecular bone. The differences decreased toward the fifth mm in a logarithmic manner. The interpretation of the logarithmic relation leads to the conclusion that the main impact of OA on bony structures is located beneath the SBP and lessens with depth. In addition to the clear difference in material with approximately 12% less bone volume in the first mm in OA patellae, the architectural arrangement is more rod-like and isotropic, accounting for an architectural decrease in stability and support. (c) 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res