Texture analysis of the radiographic trabecular bone pattern in osteoporosis

Texture is an image property which is difficult to grasp. It can be described as a "homogeneous visual pattern"l. but there exists no formal definition of texture. Intuitively people can discriminate between different textures. referring to visual clues like coarseness, orientation. periodicity, and regularity. Using such concepts, several authors have tried to quantify these aspects of texture'. However. texture encompasses more than these more or less random aspects to which the human eye is sensitive. Therefore, the majority of texture analysis algorithms is based on an image model. in which certain characteristics of the image texture are condensed. Using this image model, texture features can be derived, most of which cannot be related to visual image features. Texture analysis methods are able, in contrast to a human observer, to quantIfy textures objectively. Therefore. texture features can be used for the purpose of characterization, discrimination, and segmentation of textures in. for example, aerial and satellite imagery. Most texture analysis methods have been developed and tested on textures from the collection of texture images in Brodatz' before putting them mto use in a more realistic environment. Since the early seventies, texture analysis methods have also been applied In medical images. For example, Sulton et a!. tried to categorize different stages of pulmonary disease in radiographs4 Since then, the field of application of texture analysis methods in radiology has expanded from chest radiographs to mammograms and bone radiographs. The goal of our study is twofold: in the first place to assess the suitability of different texture analysis methods for usc in radiographs, secondly to select or develop texture features which are able to quantify the changes in the radiographic trabecular pattern occurring in osteoporosis. Osteoporosis is defined as "a disease characterized by low bone mass and microarchitectural changes of bone tissue, leading to enhanced bone fragility and a consequent increase in fracture risk." (WHO, 1994)

Bioactive glass-derived trabecular coating: a smart solution for enhancing osteointegration of prosthetic elements

In this work, the use of foam-like glass-ceramic scaffolds as trabecular coatings on ceramic prosthetic devices to enhance implant osteointegration is proposed. The feasibility of this innovative device was explored in a simplified, flat geometry: glass-ceramic scaffolds, prepared by polymeric sponge replication and mimicking the trabecular architecture of cancellous bone, were joined to alumina square substrates by a dense glass coating (interlayer). The role played by different formulations of starting glasses was examined, with particular care to the effect on the mechanical properties and bioactivity of the final coating. Microindentations at the coating/substrate interface and tensile tests were performed to evaluate the bonding strength between the sample's components. In vitro bioactive behaviour was assessed by soaking in simulated body fluid and evaluating the apatite formation on the surface and inside the pores of the trabecular coating. The concepts disclosed in the present study can have a significant impact in the field of implantable devices, suggesting a valuable alternative to traditional, often invasive bone-prosthesis fixatio

PERFORMANCE EVALUATION OF NEW IMAGING TECHNOLOGIES FOR IN VIVO ASSESSMENT OF BONE HEALTH

Research has shown that quantitative assessment of bone microstructure can be beneficial for early detection of musculoskeletal conditions such as osteoarthritis and osteoporosis. However, bone microstructure cannot be accurately measured using current generation x-ray systems due to their limited spatial resolution. Therefore, the present clinical practice relies primarily on the image-based metric of Bone Mineral Density (BMD), which does not distinguish different arrangements of trabecular microarchitecture. We investigate whether the recently introduced computed tomography (CT) scanners with enhanced spatial resolution, specifically CMOS detector-based extremity Cone Beam CT (CBCT) and ultra-high resolution multi-detector CT (UHR-MDCT, e.g. Canon Aquilion Precision CT), could potentially enable quantitative assessment of trabecular microstructure in clinical settings. This could benefit the research, early detection, and monitoring of musculoskeletal conditions. The performance of the new imaging systems is evaluated for applications in conventional Trabecular Morphometrics (including metrics of trabecular thickness, spacing, number), in classification of trabeculae into Rods and Plates, and in texture analysis. Human cadaveric bone samples are used for the assessment. The biomarker results from the new imaging systems are compared to the gold-standard micro-CT. We also assess the accuracy and reproducibility of Bone Mineral Density (BMD) measurements on extremity CMOS-CBCT using data from a pilot human subject study. The study shows that CMOS-CBCT and UHR-MDCT are able to achieve improved bone microstructure measurements compared to conventional technologies. In terms of established biomarkers such as BMD and texture features, the new imaging systems provide a good degree of reproducibility, supporting the use of CMOS-CBCT and UHR-MDCT for those biomarkers in the same manner as currently done with conventional modalities. Our results offer motivation for future clinical translation of in vivo quantitative bone microstructure evaluation using the new high resolution CT technologies

In Vivo Evaluation of 3D-Printed Silica-Based Bioactive Glass Scaffolds for Bone Regeneration

Bioactive glasses are often designed as porous implantable templates in which newly-formed bone can grow in three dimensions (3D). This research work aims to investigate the bone regenerative capability of silicate bioactive glass scaffolds produced by robocasting in comparison with powder and granule-like materials (oxide system: 47.5SiO2-10Na2O-10K2O-10MgO-20CaO-2.5P2O5, mol.%). Morphological and compositional analyses performed by scanning electron microscopy (SEM), combined with energy dispersive spectroscopy (EDS) after the bioactivity studies in a simulated body fluid (SBF) confirmed the apatite-forming ability of the scaffolds, which is key to allowing bone-bonding in vivo. The scaffolds exhibited a clear osteogenic effect upon implantation in rabbit femur and underwent gradual resorption followed by ossification. Full resorption in favor of new bone growth was achieved within 6 months. Osseous defect healing was accompanied by the formation of mature bone with abundant osteocytes and bone marrow cells. These in vivo results support the scaffold’s suitability for application in bone tissue engineering and show promise for potential translation to clinical assessment

Digital volume correlation can be used to estimate local strains in natural and augmented vertebrae: An organ-level study

Digital Volume Correlation (DVC) has become popular for measuring the strain distribution inside bone structures. A number of methodological questions are still open: the reliability of DVC to investigate augmented bone tissue, the variability of the errors between different specimens of the same type, the distribution of measurement errors inside a bone, and the possible presence of preferential directions. To address these issues, five augmented and five natural porcine vertebrae were subjected to repeated zero-strain micro-CT scan (39 μm voxel size). The acquired images were processed with two independent DVC approaches (a local and a global one), considering different computation sub-volume sizes, in order to assess the strain measurement uncertainties. The systematic errors generally ranged within ±100 microstrain and did not depend on the computational sub-volume. The random error was higher than 1000 microstrain for the smallest sub-volume and rapidly decreased: with a sub-volume of 48 voxels the random errors were typically within 200 microstrain for both DVC approaches. While these trends were rather consistent within the sample, two individual specimens had unpredictably larger errors. For this reason, a zero-strain check on each specimen should always be performed before any in-situ micro-CT testing campaign. This study clearly shows that, when sufficient care is dedicated to preliminary methodological work, different DVC computation approaches allow measuring the strain with a reduced overall error (approximately 200 microstrain). Therefore, DVC is a viable technique to investigate strain in the elastic regime in natural and augmented bones

A study of change in human trabecular bone structure with age and during osteoporosis

The objective of this work was to develop new techniques to view trabecular bone three-dimensionally, and to study its structure and the changes that occur with age and in osteoporosis; the methods used included 3D methods in the SEM, laser confocal microscopy, pseudo-holograms and a "continuous motion parallax method". A detailed analysis of trabecular bone from fourth lumbar vertebral bodies used macro-stereophotographs produced by tilting a sample 10°. Models are proposed for both normal and osteoporotic architecture. A quantitative analysis of the lengths of horizontally oriented trabeculae was carried out. A significant decrease in the number of both vertically and horizontally oriented trabeculae was found. The importance of the influence of different developmental patterns on the formation of the normal structure and of the changing vascularisation on osteoporotic structure are emphasised. Two-dimensional fast Fourier transform methods were employed to study changes in the spatial frequency of trabeculae as a function of orientation. A decrease in spatial frequency was observed in both sexes, but in males this was evident only after the mid-sixth decade in the limited sample studied. Contoured power spectra discriminated different trabecular patterns and the intensity mapping of optical density provided volume density information. Templated reverse transformation was used to study individual orientations of trabeculae. Changes in the quality of trabecular bone with age were also investigated using techniques that analyse bone before and after removal of unmineralised matrix. All specimens were less stiff after removal of osteoid; this was more marked in older specimens. Locally defective mineralisation would explain the changed behaviour observed in some old and osteoporotic specimens. Trabecular fracture patterns had a strong relationship to architecture and microstructure. Scanning electron microscopy was used to study trabecular surfaces. An uncoupling between resorption and formation was evident in older specimens. Two resorption patterns responsible for thinning and perforation and removal trabecular elements were identified. Trabecular microfractures were also investigated

Foam replica method in the manufacturing of bioactive glass scaffolds: Out-of-date technology or still underexploited potential?

Since 2006, the foam replica method has been commonly recognized as a valuable technology for the production of highly porous bioactive glass scaffolds showing three-dimensional, open-cell structures closely mimicking that of natural trabecular bone. Despite this, there are important drawbacks making the usage of foam-replicated glass scaffolds a difficult achievement in clinical practice; among these, certainly the high operator-dependency of the overall manufacturing process is one of the most crucial, limiting the scalability to industrial production and, thus, the spread of foam-replicated synthetic bone substitutes for effective use in routine management of bone defect. The present review opens a window on the versatile world of the foam replica tech-nique, focusing the dissertation on scaffold properties analyzed in relation to various processing parameters, in order to better understand which are the real issues behind the bottleneck that still puts this technology on the Olympus of the most used techniques in laboratory practice, without moving, unfortunately, to a more concrete application. Specifically, scaffold morphology, mechanical and mass transport properties will be reviewed in detail, considering the various templates proposed till now by several research groups all over the world. In the end, a comprehensive overview of in vivo studies on bioactive glass foams will be provided, in order to put an emphasis on scaffold performances in a complex three-dimensional environment

Development of osteoconductive coatings for non-metallic bone implants

2008/2009The design of osseous implants, either load bearing or not, with desired mechanical and surface features that promote integration with bone and avoid risks of bone resorption and implant failure due to shear stresses, is still a challenging endeavour. The mechanical stresses which the skeleton undergoes affect bone formation and resorption processes. Bone remodelling is often promoted by adequate stress/strain conditions which are able to prevent bone mass loss. The largely used metallic implants offer several advantages like easy shape casting and modelling but include also several drawbacks like high stiffness if compared with the mechanical properties of native bone. A new generation of bone prosthesis is therefore indispensable to overcome the limitations of the obsolete metallic devices. In the orthopaedic framework, promising results have been achieved in the recent decades by three-dimensional structures named scaffolds. It is mandatory for any optimal scaffold to act as a temporary three-dimensional support for cell adhesion, growth and mineral matrix deposition. Moreover, ideal scaffolds should be able to integrate into surrounding tissue and mimic the structure and morphology of the natural bone tissue. Strict requirements for scaffolds are biocompatibility, a design closely resembling the natural extracellular matrix, an appropriate surface chemistry to promote cellular attachment, differentiation and proliferation and a sufficient mechanical strength to withstand in vivo stresses and physiological loading. Finally, the degradation of the ideal scaffold should proceed in a controlled way, keeping a sufficient structural integrity until the newly grown tissue has replaced the scaffold's supporting functions. Coupling a three-dimensional porous scaffold and a load bearing structure with suitable mechanical properties it is possible to obtain a device where the osteoconductive and osteoinductive properties of the former are synergistically linked with the mechanical ones of the latter. In this work both the aspects – osteointegration and load bearing – of an ideal prosthesis have been investigated. Alginate/Hydroxyapatite composite scaffolds were developed to be used either as scaffolds for sub-critical defects or as coatings for load bearing non-metallic bone prostheses. In both cases the investigation aimed to select suitable components and casting procedures to obtain the best results. The features of the single components and of the final three-dimensional structure were extensively investigated in order to obtain the most clarifying characterization both in terms of physical-chemical properties and in terms of biological responsiveness. The experimental section of this work involved physical-chemical analysis that helped to characterize both the organic and the inorganic components of the scaffold, respectively alginate and hydroxyapatite, before and after composite assembling. This investigation, based on several techniques (NMR, Rheology, XRD, Raman and TEM) allowed to characterize in detail the scaffold’s components and revealed the possibility of using the hydroxyapatite as a source of calcium ions for the gelification of the alginate without loosing the paramount osteoinductive properties of the mineral. Micro Computed Tomography (µ-CT) was employed to understand quantitatively the architectural features of the three-dimensional matrix obtained after alginate gel casting process. Moreover, this tool allowed to assess the influence of different manufacturing protocols (e.g. concentration of the components, casting temperatures) on the scaffold’s final structure. The results obtained by means of µ-CT coupled with the ones of Scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) analysis of the scaffolds showed an optimal interconnected porous structure with pore sizes ranging between 100 m and 300 m and over 88% porosity. Proliferation assays and SEM observations demonstrated that human osteosarcoma cell lines were able to proliferate, maintain osteoblast-like phenotype and massively colonize the scaffold structure. Once the in vitro behaviour of the structure was clear, in vivo tests were performed. Cone-like Alg/HAp scaffolds were tested on skeletally mature female New Zealand White rabbits and compared with positive (bioactive glass scaffold) and negative (without any implant) controls. Ex vivo investigations of the dissected samples were based on µ-CT and histological analysis and revealed high level of osteointegration and osteoconduction of the scaffolds. Moreover, efforts have been made to link the porous structure to the non-metallic fibre reinforced composite used as load bearing unit. Overall, these combined results indicate that the structure here developed is promising for being employed in orthopaedic applications.XXII Ciclo197

The use of digital image correlation in the biomechanical area: a review

This paper offers an overview of the potentialities and limitations of digital image correlation (DIC) as a technique for measuring displacements and strain in biomechanical applications. This review is mainly intended for biomechanists who are not yet familiar with DIC. This review includes over 150 papers and covers different dimensional scales, from the microscopic level (tissue level) up to macroscopic one (organ level). As DIC involves a high degree of computation, and of operator- dependent decisions, reliability of displacement and strain measurements by means of DIC cannot be taken for granted. Methodological problems and existing solutions are summarized and compared, whilst open issues are addressed. Topics addressed include: preparation methods for the speckle pattern on different tissues; software settings; systematic and random error associated with DIC measurement. Applications to hard and soft tissues at different dimensional scales are described and analyzed in terms of strengths and limitations. The potentialities and limitations of DIC are highlighted, also in comparison with other experimental techniques (strain gauges, other optical techniques, digital volume correlation) and numerical methods (finite element analysis), where synergies and complementarities are discussed. In order to provide an overview accessible to different scientists working in the field of biomechanics, this paper intentionally does not report details of the algorithms and codes used in the different studies