Imaging a microfocus X-ray focal spot with a thin coded aperture.

Imaging of the focal spot size in X-ray generators can be achieved by means of a pinhole in a highly attenuating material, such as gold. For microfocus generators with spot sizes of only around 10 microns or less, the material must be very thin to avoid an impractical aspect ratio. With a 90 kV source, only 11% attenuation is attained with 5 µm gold. For a pinhole that is smaller than the focal spot, the signal-to-noise ratio (SNR) may be less than 1. To image the focal spot of a medical X-ray generator, a coded aperture has been used previously to reduce the exposure time required, however the same technique does not appear to have been used to increase the SNR when the attenuation is very low. Such a method is used here, using a no-two-holes-touching variation of a modified uniformly redundant array (MURA). In a prototype sample, with only 5 µm gold having 2.75 µm holes, the focal spot of a microfocus X-ray generator used in a micro-CT system could be clearly visualised and quantified. Directionality of the aberrations made focussing of the X-ray spot more intuitive and reduced the time required to obtain an optimal, quantifiable focus.

Development of two-dimensional beam hardening correction for X-ray micro-CT.

BACKGROUND: Beam-hardening in tomography with polychromatic X-ray sources results from the nonlinear relationship between the amount of substance in the X-ray beam and attenuation. Simple linearisation curves can be derived with the use of an appropriate step wedge, however, this does not yield good results when different materials are present whose relationships between X-ray attenuation and energy are very different. OBJECTIVE: To develop a more accurate method of beam-hardening correction for two-phase samples, particularly immersed or embedded biological hard tissue. METHODS: Use of a two-dimensional step wedge is proposed in this study. This is not created physically but is derived from published X-ray attenuation coefficients in conjunction with a modelled X-ray spectrum, optimised from X-ray attenuation measurements of a calibration carousel. To test this method, a hydroxyapatite disk was scanned twice; first dry, and then immersed in 70% ethanol solution (commonly used to preserve biological specimens). RESULTS: With simple linearisation the immersed disk reconstruction exhibited considerable residual beam hardening, with edges appearing approximately 10% more attenuating. With 2-dimensional correction, the attenuation coefficient showed only around 0.5% deviation from the dry case. CONCLUSION: Two-dimensional beam-hardening correction yielded accurate results and does not require segmentation of the two phases individually.

Mineral exchange within restorative materials following incomplete carious lesion removal using 3D non-destructive XMT subtraction methodology.

OBJECTIVES: The objective of this study was to quantify the changes in mineral and selected element concentrations within residual carious dentine and restorative materials following incomplete carious lesion removal (ICLR) using different cavity liners, with non-destructive subtraction 3D-X-ray Microtomography (XMT, QMUL, London, UK). MATERIALS AND METHODS: A total of 126 extracted teeth with deep dental caries were assessed using International Caries Risk and Assessment (ICDAS). Eight teeth were subsequently selected after radiographic evaluation. Each lesion was removed, leaving a thin layer of leathery dentine at the deepest part of cavity. Different cavity lining materials were placed; Mineral Trioxide Aggregate (MTA), calcium hydroxide, (Ca(OH)2), resin-based material (RBM). For each, the restorative material was an encapsulated glass ionomer (GIC) and the control group had a GIC restoration alone. Each tooth was immediately placed in Simulated Body Fluid (SBF). All samples were then imaged using XMT at baseline, and three weeks after treament. The XMT images were then subtracted to show the mineral concentration changes three weeks after treatment. RESULTS: There were significant increases in mineral concentrations within the residual demineralised dentine in individual teeth treated with Ca(OH)2, MTA, RBM, and GIC following immersion in SBF for three weeks. GIC group without any liners showed the greatest increase in mineral concentration, followed by MTA and Ca(OH)2. CONCLUSION: Mineral changes in demineralised dentine and within restorative materials are quantifiable using non-destructive 3D-XMT subtraction methodology. This laboratory study suggested that calcium, phosphate and strontium ion-exchange occurs with GIC, MTA and Ca(OH)2 in deep dentinal lesions following ICLR. CLINICAL RELEVANCE: In clinical practice, incomplete carious lesion removal could be performed to avoid the dental pulp exposure. 3D non-destructive XMT subtraction methodology in a laboratory setting is advantageous to provide evidence for different restorative materials on deep carious lesions prior to clinical investigations.

Virtual Recovery of Content from X-Ray Micro-Tomography Scans of Damaged Historic Scrolls.

There is a large body of historical documents that are too fragile to be opened or unrolled, making their contents inaccessible. Recent improvements in X-ray scanning technology and computer vision techniques make it possible to perform a "virtual" unrolling of such documents. We describe a novel technique to process a stack of 3D X-ray images to identify the surface of parchment scrolls, unroll them, and create a visualization of their written contents. Unlike existing techniques, we can handle even challenging cases with minimal manual interaction. Our novel approach was deployed on two 15th and 16th century damaged historic scrolls from the manors of Bressingham and Diss Heywood. The former has become fused, probably due to exposure to moisture, and cannot be fully unrolled. The latter was severely burnt several hundred years ago, becoming thoroughly charred, heat-shrunken, and distorted, with all the sheets now brittle and fused together. Our virtual unrolling revealed text that has been hidden for centuries.

Comparison of efficacy of dental varnish containing fluoride either with CPP-ACP or bioglass on root caries: Ex vivo study.

OBJECTIVES: To compare the efficacy of fluoride varnishes either casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) or bioglass particles on the severity index of root caries. METHODS: Visual-tactile assessments including lesion hardness was carried out to categorise the severity index of 80 extracted teeth with primary root caries. These teeth were randomly divided into four groups; CPP-ACP and fluoride, bioglass and fluoride, fluoride only, and no treatment. Standardised toothbrushing using a dentifrice containing 1450 ppm fluoride was carried out twice a day for all groups. All samples were stored in remineralising solution at 37°C for 45 days. Visual-tactile assessments were carried out at baseline, and after 45 days. Surface roughness measurements (Ra) were performed at baseline and after 7, 14, 30 and 45 days. X-ray Microtomography was performed at the baseline and after 45 days for three samples from each group to quantify the change in mineral contents in the lesion area. RESULTS: The Visual-tactile assessment results showed a reduction in the severity index of root caries, being 20% in CPP-ACP and fluoride, 100% in bioglass and fluoride, 80% in fluoride only, and 60% in non-varnish (toothbrushing only). Non-significant change in surface roughness was observed in all groups. X-ray Microtomography assessment showed a highly significant increase in the mineral deposition in all cases (p > .001). CONCLUSION: The combination of bioglass with fluoride has a potentially superior effect than either CPP-ACP with fluoride or fluoride only to reverse and arrest the root caries in a laboratory setting. CLINICAL SIGNIFICANCE: The combination of bioglass particles and fluoride formulation is likely to have a significant impact in reversing and arresting root caries in a minimally invasive approach. However, randomised controlled double-blinded clinical trials are required to translate these results into clinical practice.

Body wall structure in the starfish Asterias rubens.

The body wall of starfish is composed of magnesium calcite ossicles connected by collagenous tissue and muscles and it exhibits remarkable variability in stiffness, which is attributed to the mechanical mutability of the collagenous component. Using the common European starfish Asterias rubens as an experimental animal, here we have employed a variety of techniques to gain new insights into the structure of the starfish body wall. The structure and organisation of muscular and collagenous components of the body wall were analysed using trichrome staining. The muscle system comprises interossicular muscles as well as muscle strands that connect ossicles with the circular muscle layer of the coelomic lining. The collagenous tissue surrounding the ossicle network contains collagen fibres that form loop-shaped straps that wrap around calcite struts near to the surface of ossicles. The 3D architecture of the calcareous endoskeleton was visualised for the first time using X-ray microtomography, revealing the shapes and interactions of different ossicle types. Furthermore, analysis of the anatomical organisation of the ossicles indicates how changes in body shape may be achieved by local contraction/relaxation of interossicular muscles. Scanning synchrotron small-angle X-ray diffraction (SAXD) scans of the starfish aboral body wall and ambulacrum were used to study the collagenous tissue component at the fibrillar level. Collagen fibrils in aboral body wall were found to exhibit variable degrees of alignment, with high levels of alignment probably corresponding to regions where collagenous tissue is under tension. Collagen fibrils in the ambulacrum had a uniformly low degree of orientation, attributed to macrocrimp of the fibrils and the presence of slanted as well as horizontal fibrils connecting antimeric ambulacral ossicles. Body wall collagen fibril D-period lengths were similar to previously reported mammalian D-periods, but were significantly different between the aboral and ambulacral samples. The overlap/D-period length ratio within fibrils was higher than reported for mammalian tissues. Collectively, the data reported here provide new insights into the anatomy of the body wall in A. rubens and a foundation for further studies investigating the structural basis of the mechanical properties of echinoderm body wall tissue composites.

Microscopic study of dental hard tissues in primary teeth with Dentinogenesis Imperfecta Type II: Correlation of 3D imaging using X-ray microtomography and polarising microscopy.

OBJECTIVES: The aim of this study was to examine the histological appearance of dental hard tissues in primary teeth from children with DI using conventional polarised light microscopy and correlate that with 3D imaging using X-ray microtomograpy (XMT) to gain a further understanding of the dentine structure of teeth diagnosed with dentinogenesis imperfecta. DESIGN: Undecalcified sections of primary teeth from patients diagnosed with Dentinogenesis Imperfecta Type II were examined using polarised light microscopy. XMT was employed for 3D-imaging and analysis of the dentine. RESULTS: The polarised light microscopy and XMT revealed tubular structures in the dentine seen as vacuoles coinciding with the path of normal dentinal tubules but not continuous tubules. The size of the tubules was close to that of capillaries. The largest tubular structures had a direction corresponding to where the pulp tissue would have been located during primary dentine formation. The dysfunctional mineralisation of the dentine and obliteration of the pulp evidently leaves blood vessels in the dentine which have in the main been tied off and, in the undecalcified sections, appear as vacuoles. CONCLUSIONS: Although from radiographs, the pulp in teeth affected by Dentinogenesis Imperfect type II appears to be completely obliterated, a network of interconnected vessels may remain. The presence of large dentinal tubules and blood vessels, or the remnants of blood vessels, could provide a pathway for bacteria from the oral cavity. This might account for why some of these teeth develop periapical abscesses in spite of apparently having no pulp.

Mapping the spatial and temporal progression of human dental enamel biomineralization using synchrotron X-ray diffraction.

OBJECTIVE: The complex biological, physicochemical process of human dental enamel formation begins in utero and for most teeth takes several years to complete. Lost enamel tissue cannot regenerate, therefore a better understanding of the spatial and temporal progression of mineralization of this tissue is needed in order to design improved in vivo mineral growth processes for regenerative dentistry and allow the possibility to grow a synthetic whole or partial tooth. METHOD: Human dental enamel samples across a range of developmental stages available through archaeological collections have been used to explore the spatial and temporal progression of enamel biomineralization. Position sensitive synchrotron X-ray diffraction was used to quantify spatial and temporal variations in crystallite organization, lattice parameters and crystallite thickness at three different stages in enamel maturation. In addition X-ray microtomography was used to study mineral content distributions. RESULTS: An inverse correlation was found between the spatial variation in mineral content and the distribution of crystallite organization and thickness as a function of time during enamel maturation. Combined X-ray microtomography and synchrotron X-ray diffraction results show that as enamel matures the mineral content increases and the mineral density distribution becomes more homogeneous. Starting concurrently but proceeding at a slower rate, the enamel crystallites become more oriented and larger; and the crystallite organization becomes spatially more complex and heterogeneous. CONCLUSION: During the mineralization of human dental enamel, the rate of mineral formation and mineral organization are not identical. Whilst the processes start simultaneously, full mineral content is achieved earlier, and crystallite organization is slower and continues for longer. These findings provide detailed insights into mineral development in human dental enamel which can inform synthetic biomimetic approaches for the benefit of clinical dentistry.

Quantitative high contrast X-ray microtomography for dental research.

OBJECTIVES: X-ray microtomography (XMT or micro-CT) is a miniaturized version of medical CT and has been used extensively for in vitro dental research. The technique allows three-dimensional analyses of both structure and density (or concentration), the latter requiring some a priori knowledge of composition. The aim of this paper is to demonstrate the capabilities of an XMT scanner specifically designed for dental research, especially that requiring high contrast resolution or accurate mineral concentration quantification. METHODS: The MuCAT scanners designed at Queen Mary, University of London, use high dynamic range CCD cameras with time-delay integration readout to provide high quality tomographic images. Accuracy in mineral concentration quantification is achieved using a modelling approach to beam hardening correction with automatic calibration following every scan. Accuracy was tested by measuring the density of a hydroxyapatite disc, and the utility of the high contrast and high accuracy capabilities are demonstrated in three applications from ongoing dental research projects. RESULTS: Quantification accuracy in the hydroxyapatite disc density was better than 1%. In dental applications, slight differences in mineral concentration allowed features such as dead tracts to be visualized and ion transport from a glass-ionomer cement into demineralized dentine to be observed. CONCLUSION: The improved accuracy and contrast sensitivity, together with the non-destructive nature of XMT in general, facilitates precise studies of dynamic processes in teeth. The ability to differentiate subtle differences in mineral concentration allows dead tracts to be traced in three dimensions, linking external pathology in teeth to reactive processes from the pulp. CLINICAL SIGNIFICANCE: The MuCAT scanners have been optimized for quantification of mineral concentration and are particularly useful for in vitro studies of de- and re-mineralization, excavation and other treatment methodologies, and for gaining further insight into tooth morphology and pathology. Results from such studies will inform development of clinical treatment and management.

Quantification of residual dentine thickness following crown preparation.

OBJECTIVES: Pulpal response to tooth preparation is a major concern in fixed prosthodontics. Research has suggested that 2mm or more of remaining dentine is critical in protecting the pulp following tooth preparation. However, clinicians have no means of knowing dentine thickness either before or after preparation and therefore lack feedback about this important aspect of preparation quality. The aim of this project was to develop a method for measuring local dentine thickness following tooth preparation for metal ceramic crowns, in vitro, which could be used as a tool to evaluate preparation technique and instrumentation. METHODS: Microtomography (XMT or micro-CT) scans were taken of extracted teeth before and after crown preparation. Local dentine thickness was defined for every voxel within the 3D tooth image as the sum of distances from that voxel to the pulp and to the anatomical surface. The method also allows the thickness of material removed to be quantified. Three-dimensional colour-coded maps of dentine thickness were generated, and the distributions of dentine thickness throughout the teeth were analysed. This was tested by a single operator on sixteen extracted upper central incisors. RESULTS: This method enabled clear visualisation and analysis of residual dentine thickness. In the trial, it revealed consistent over-prepared regions along the labial proximal line angles which, in a clinical case, could affect subsequent tooth and restoration longevity. All but one of the prepared teeth had regions with a residual dentine thickness of less than 1.5mm, in 6 it was less than 1.0mm and in 3 of these it was less than 0.5mm. CONCLUSION: Although ex vivo, this method can be used as a research tool to look for patterns of over- or under-preparation, leading to possible modification of technique, instrumentation and, or crown design. CLINICAL SIGNIFICANCE: It is not currently possible for clinicians to know the thickness of residual dentine following crown preparation, a key factor in long term outcome. The described method of quantifying and visualising this thickness allows preparation techniques and instrumentation to be evaluated in vitro, leading to prospective improvements in clinical procedures.

Diffusive transport within dentinal tubules: an X-ray microtomographic study.

The hydrodynamic theory of dentine hypersensitivity proposes that external stimuli cause dentinal fluid movement within dentinal tubules thereby triggering mechanosensitive nerves and eliciting a pain response. The aim of this study was to employ X-ray microtomography (XMT) to monitor diffusion of caesium acetate through dentine to investigate the extent to which transport occurs within the primary tubules compared to that through branched microtubules believed to run perpendicular to the direction of the primary dentinal tubules. 2.0-mm thick coronal dentine disks masked to leave half of the upper surface exposed were imaged by XMT, initially in water, which was then replaced with an aqueous solution of 0.50 mol l(-1) caesium acetate. Further XMT images were acquired after 1 and 6 days immersion. The XMT images were used to measure the change in the X-ray linear attenuation coefficient resulting from caesium acetate ingress into dentine. There was clearly considerable ingress of caesium acetate into the dentine lying below the exposed surface, but considerably less beneath the sealed surface, suggesting that diffusive transport occurs predominantly in the direction of the primary dentinal tubules, with no significant lateral transport. Primary tubules are clearly the dominant transmission route for triggering the mechanosensitive nerves present at the dentine-pulp interface, and for delivery of nerve desensitising agents.

Three-dimensional study of human dental fissure enamel by synchrotron X-ray microtomography.

The three-dimensional morphology of human tooth fissures and the quantification of mineral distribution in fissure enamel are pertinent to the development and diagnosis of caries. Synchrotron X-ray microtomography was used to measure linear attenuation coefficients (at 25 keV) at high spatial resolution with a volume-imaging element (cubic voxel) of 4.9x4.9x4.9 microm3 in a block from a human premolar that included part of a stained fissure. From the linear attenuation coefficient, the mineral concentration, expressed as gHAp cm-3 (where HAp is stoichiometric hydroxyapatite), was calculated. The mean mineral concentration in bulk enamel was 2.84 gHAp cm-3. Well-defined regions (1.5-2.6 gHAp cm-3), extending up to approximately 130 microm from the base of some narrower lengths of the fissure and up to approximately 50 microm deep from the fissure surface, were attributed to hypomineralization. Other regions of low mineral concentration, some (1.4-2.3 gHAp cm-3) lying within the expected course of the fissure base and some (2.2-2.7 gHAp cm-3) deep to the pit, were also considered to be of developmental origin. However, a diffuse distribution of low mineral concentrations (2.2-2.7 gHAp cm-3) in the pit walls was attributed primarily to demineralization from caries. The fissure contained heterogeneous material (

Non-destructive studies of tissue-engineered phalanges by magnetic resonance microscopy and X-ray microtomography.

One of the intents of tissue engineering is to fabricate biological materials for the augmentation or replacement of impaired, damaged, or diseased human tissue. In this context, novel models of the human phalanges have been developed recently through suturing of polymer scaffolds supporting osteoblasts, chondrocytes, and tenocytes to mimic bone, cartilage, and tendon, respectively. Characterization of the model constructs has been accomplished previously through histological and biochemical means, both of which are necessarily destructive to the constructs. This report describes the application of two complementary, non-destructive, non-invasive techniques, magnetic resonance microscopy (MRM) and X-ray microtomography (XMT or quantitative computed tomography), to evaluate the spatial and temporal growth and developmental status of tissue elements within tissue-engineered constructs obtained after 10 and 38 weeks of implantation in athymic (nude) mice. These two times represent respective points at which model middle phalanges are comprised principally of organic components while being largely unmineralized and later become increasingly more mineralized. The spatial distribution of mineralized deposits within intact constructs was readily detected by XMT (qCT) and was comparable to low intensity zones observed on MRM hydration maps. Moreover, the MRM-derived hydration values for mineralized zones were inversely correlated with mineral densities measured by XMT. In addition, the MRM method successfully mapped fat deposits, collagenous tissues, and the hydration state of the soft tissue elements comprising the specimens. These results support the application of non-destructive, non-invasive, quantitative MRM and XMT for the evaluation of constituent tissue elements within complex constructs of engineered implants.

Dentin exposure in tooth preparations for porcelain veneers: a pilot study.

STATEMENT OF PROBLEM: The various clinical techniques available for even reduction of a tooth surface to receive a porcelain veneer restoration do not produce a consistently even conservative reduction. In addition, it is not known which technique is most conservative of enamel. PURPOSE: The purpose of this pilot study was to assess the effectiveness of 3 clinical techniques, namely, dimple, depth groove, and freehand, in producing an intraenamel preparation. The relation between overpreparation beyond the commonly accepted depth of preparation of 0.5 mm and dentin exposure was also examined. MATERIAL AND METHODS: A single operator prepared 3 groups of 5 extracted maxillary central incisors to a depth of 0.5 mm using dimple, depth-groove, and freehand methods of tooth preparation. The prepared teeth were scanned using an x-ray microtomography scanner. The reconstructed images were studied using software that provided a volume-rendering routine so that, by choosing suitable x-ray linear attenuation coefficient thresholds, enamel (2.78 cm(-1) at 40 keV) and dentin (1.63 cm(-1) at 40 keV) surfaces could be viewed. The percentage area of enamel conserved was analyzed from these images. Coordinate metrology was used to produce color-coded images depicting the depth of preparation. The Kruskal-Wallis test was used to determine the statistical significance (alpha=.05) in the difference between the mean percentage area of enamel conserved in the 3 technique groups. The coordinate metrology and x-ray microtomography images were visually compared to study the correlation between overpreparation and dentin exposure. RESULTS: The Kruskal-Wallis test did not demonstrate significant difference (P=.07) between the 3 techniques in conserving enamel. However, the dimple technique showed a greater trend to retaining a larger mean percentage area of enamel (77.5% +/- 14.2) compared to depth-groove (50.1% +/- 17.5) and freehand (76.8% +/- 24.4) techniques. Preparation depth in the range of 0.4 to 0.6 mm was largely seen to be intraenamel, except in the cervical region. CONCLUSION: Within the limitations of this pilot study, the 3 different techniques tested did not differ significantly in conserving enamel.

Modulation of mastication during experimental loosening of complete dentures.

PURPOSE: Suction is achieved when complete dentures are first fitted, but it fades during the months following insertion, when it is increasingly complemented by muscular denture control. The aim of this study was therefore to investigate the extent to which patterns of mastication are altered by experimental failure of physical retention. MATERIALS AND METHODS: Seven edentulous volunteers had maxillary replica dentures made, with fine tubes incorporated so that alternating positive and negative air pressure could be generated under the fitting surface. Mandibular movements, EMG, and pressure under the denture base were recorded during unilateral chewing. RESULTS: The change of physical retention passed undetected by all subjects; they continued chewing apparently undisturbed. However, during air injection, the mandibular excursions were slightly slower (nonsignificant) and demonstrated a reduced variance (P < or = .05). The muscle activity showed significantly longer bursts (P < or = .05), and peak activity occurred later in the cycle (nonsignificant). CONCLUSION: Sudden failure of denture retention seems to initiate an immediate and effective modulation of centrally generated muscular activity patterns.