Non-invasive X-ray Microtomography Research Articles

Asbestos bodies count and morphometry in bulk lung tissue samples by non-invasive X-ray micro-tomography

The number of the Asbestos Bodies (AB), i.e. asbestos that developed an iron-protein coating during its permanence in biological tissues, is one of the most accessible markers of asbestos exposure in individuals. The approaches developed to perform AB count in biological tissues are based on the manual examination of tissue digests or histological sections by means of light or electron microscopies. Although these approaches are well established and relatively accessible, manual examination is time-consuming and can be reader-dependent. Besides, approximations are applied because of the limitations of 2D readings and to speed up manual counts. In addition, sample preparation using tissue digests require an amount of tissue that can only be obtained by invasive surgery or post-mortem sampling. In this paper, we propose a new approach to AB counting based on non-destructive 3D imaging, which has the potential to overcome most of the limitations of conventional approaches. This method allows automating the AB count and determining their morphometry distribution in bulk tissue samples (ideally non-invasive needle biopsies), with minimal sample preparation and avoiding approximations. Although the results are promising, additional testing on a larger number of AB-containing biological samples would be required to fully validate the method.

The True Identity of Putative Tooth Alveoli in a Cenozoic Crown Bird, the Gastornithid Omorhamphus

All extant birds are toothless, and recent molecular evidence suggests that edentulism in extant birds is the product of a single evolutionary transition to toothlessness on the line to crown birds in the Cretaceous. However, a fossil crown bird premaxilla from the Palaeogene of North America (assigned to the gastornithid Omorhamphus storchii) has been interpreted as bearing alveoli for teeth, an observation that would cast doubt on a single loss of teeth preceding the extant avian radiation. However, the identity of these putative alveoli has never been reinvestigated in detail. Here, we re-examine this problematic juvenile specimen, using non-invasive x-ray microtomography, enabling the assessment of the true identity of the large, alveolus-like pits on the ventral side of this premaxilla. Although superficially alveolus-like, we illustrate that these pits represent openings of large neurovascular canals communicating with both the medullary cavity as well as other canals opening along the dorsal and lateral surfaces of the upper jaw, and that none of these openings appear to represent tooth alveoli. Further, we demonstrate that claims of an adult gastornithid specimen (Gastornis parisiensis) exhibiting tooth alveoli are similarly unfounded. By rejecting the hypothesis of dentition in these gastornithids, we eliminate any lingering uncertainty regarding the persistence of teeth within the avian crown group. We illustrate the presence of similar large vascular openings along the ventral surface of the beak of juvenile Gastornis russelli/parisiensis, and smaller versions in the juvenile premaxillae of Sylviornis neocaledoniae. We suggest that the large vascular canals in gastornithid specimens such as O. storchii are a feature associated with rapid growth of the juvenile beak, allowing the attainment of a large and dorsoventrally deep beak early in ontogeny. This may have enabled young gastornithids to become autonomous early, consistent with a presumably precocial developmental strategy.

Pore system characteristics of soil aggregates and their relevance to aggregate stability

Aggregates are the structural units of soils, and the physical stability is considered to be a keystone parameter of soil quality. However, little is known about the evolution of the pore system in aggregates and its importance in defining aggregate stability. In this paper, we investigated the pore system and stability of three dominant macroaggregate sizes (1–2, 2–5 5–10 mm) obtained from a fine sand-loamy Chernozem under three distinct land uses (arable, grassland and forest). We used non-invasive X-ray microtomography (XMT) in combination with pore network extraction to characterise PSD (pore size distribution) of aggregates and their potential changes upon continued submergence in water. We showed that smaller aggregates (1–2 mm) have significantly higher total X-ray resolvable porosity than the medium (2–5 mm) and large (5–10 mm) aggregates. Also, using imaging tools, we demonstrated for the first time, that the pore system of stable aggregates from grassland and forest does not undergo significant changes upon continued submergence in water. It can be hypothesised that a physically stable pore structure allows the storage and transmission of water without a structural collapse, thereby contributing to aggregate stability. We found statistically significant positive correlations between different pore groups (closed pores, water holding pores and air space spores) and water stability of aggregates from all three land uses suggesting that pore system characteristics play a significant role in aggregate stability. Our results suggest that PSD is an important factor that determines the stability of soil aggregates.

An inconvenient truth about xylem resistance to embolism in the model species for refilling Laurus nobilis L.

Direct, non-invasive X-ray microtomography and optical technique observations applied in stems and leaves of intact seedlings revealed that laurel is highly resistant to drought-induced xylem embolism. Contrary to what has been brought forward, daily cycles of embolism formation and refilling are unlikely to occur in this species and to explain how it copes with drought. There has been considerable controversy regarding xylem embolism resistance for long-vesselled angiosperm species and particularly for the model species for refilling (Laurus nobilis L.). The purpose of this study was to resolve the hydraulic properties of this species by documenting vulnerability curves of different organs in intact plants. Here, we applied a direct, non-invasive method to visualize xylem embolism in stems and leaves of intact laurel seedlings up to 2-m tall using X-ray microtomography (microCT) observations and the optical vulnerability technique. These approaches were coupled with complementary centrifugation measurements performed on 1-m long branches sampled from adult trees and compared with additional microCT analyses carried out on 80-cm cut branches. Direct observations of embolism spread during desiccation of intact laurels revealed that 50% loss of xylem conductivity (Ψ50) was reached at − 7.9 ± 0.5 and − 8.4 ± 0.3 MPa in stems and leaves, respectively, while the minimum xylem water potentials measured in the field were − 4.2 MPa during a moderate drought season. Those findings reveal that embolism formation is not routine in Laurus nobilis contrary to what has been previously reported. These Ψ50 values were close to those based on the flow-centrifuge technique (− 9.2 ± 0.2 MPa), but at odds with microCT observations of cut branches (− 4.0 ± 0.5 MPa). In summary, independent methods converge toward the same conclusion that laurel is highly resistant to xylem embolism regardless its development stage. Under typical growth conditions without extreme drought events, this species maintains positive hydraulic safety margin, while daily cycles of embolism formation and refilling are unlikely to occur in this species.

The impact of green roof ageing on substrate characteristics and hydrological performance

Green roofs contribute to stormwater management through the retention of rainfall and the detention of runoff. However, there is very limited knowledge concerning the evolution of green roof hydrological performance with system age. This study presents a non-invasive technique which allows for repeatable determination of key substrate characteristics over time, and evaluates the impact of observed substrate changes on hydrological performance.The physical properties of 12 green roof substrate cores have been evaluated using non-invasive X-ray microtomography (XMT) imaging. The cores comprised three replicates of two contrasting substrate types at two different ages: unused virgin samples; and 5-year-old samples from existing green roof test beds. Whilst significant structural differences (density, pore and particle sizes, tortuosity) between virgin and aged samples of a crushed brick substrate were observed, these differences did not significantly affect hydrological characteristics (maximum water holding capacity and saturated hydraulic conductivity). A contrasting substrate based upon a light expanded clay aggregate experienced increases in the number of fine particles and pores over time, which led to increases in maximum water holding capacity of 7%. In both substrates, the saturated hydraulic conductivity estimated from the XMT images was lower in aged compared with virgin samples. Comparisons between physically-derived and XMT-derived substrate hydrological properties showed that similar values and trends in the data were identified, confirming the suitability of the non-invasive XMT technique for monitoring changes in engineered substrates over time.The observed effects of ageing on hydrological performance were modelled as two distinct hydrological processes, retention and detention. Retention performance was determined via a moisture-flux model using physically-derived values of virgin and aged maximum water holding capacity. Increased water holding capacity with age increases the potential for retention performance. However, seasonal variations in retention performance greatly exceed those associated with the observed age-related increases in water holding capacity (+72% vs +7% respectively). Detention performance was determined via an unsaturated-flow finite element model, using van Genuchten parameters and XMT-derived values of saturated hydraulic conductivity. Reduced saturated hydraulic conductivity increases detention performance. For a 1-hour 30-year design storm, the peak runoff was found to be 33% lower for the aged brick-based substrate compared with its virgin counterpart.

Combined methodologies for three-dimensional reconstruction of fossil plants preserved in siderite nodules: Stephanospermum braidwoodensis nov. sp. (Medullosales) from the Mazon Creek lagerstätte

A new species of Medullosan ovule from the Mazon Creek Carboniferous lagerstätte is documented using a novel combination of non-invasive X-Ray Micro-Tomography (XMT) and orientated precision sectioning based on the XMT results. 3-D reconstruction of the ovule has correlated geometries of different layers with tissue characteristics gathered from wafered sections, with the methodological combination presenting a virtual reconstruction of the specimen and also enabling positioning of serial sections of the holotype in pre-determined positions. Stephanospermum braidwoodensis sp. nov. has four longitudinally orientated sarcotestal wings, two to each side of the major plane that demonstrate 180° rotational (bilateral) symmetry, while the sclerotesta has three prominent longitudinal commissural ribs and the pollen chamber has three small ribs and triangular nucellar beak, both demonstrating radial (threefold) symmetry. This demonstration of both radial and bilateral symmetries in different tissues emphasises the complexities of inferring systematic affinities of fossil seeds from symmetry alone. We consider S. braidwoodensis to be closely related to the co-occurring S. konopeonus Drinnan et al., and postulate that it was born on a fertile truss similar to that of the latter species. Finally implications of our findings for the utility of these methods in identifying additional species from the Mazon Creek biota are discussed, and the advantages and disadvantages of different methods of nodule preparation are considered. We conclude that additional species are likely to be recognised from the Mazon Creek flora by application of the same methodologies used in this investigation.

Cellular architecture and its relationship with mechanical properties in expanded extrudates containing apple pomace

Cereal-based puffed foods can deliver significant amounts of fruit and vegetable fiber, however a major hurdle is the accompanying decrease in expansion and poor textural properties. The objective of this work was to develop a comprehensive understanding of the operative rheology, processing conditions, cellular architecture, macrostructure and mechanical properties of high fiber, starch-based expanded matrices produced using extrusion. The combination of phase transition analysis and non-invasive X-ray microtomography provided a unique analytical approach for this purpose. A lab-scale twin screw extruder was used for processing directly expanded products from corn flour and apple pomace blends containing up to 22.5% total dietary fiber. Different levels of pomace (0–28%) and in-barrel processing moisture (17.5–25%) resulted in extrudates with a wide range of microstructures (average cell size 0.05–3.43mm, wall thickness 0.12–0.34mm and void fraction 0.53–0.76). Structural anisotropy biased towards radial expansion was observed in foams without pomace, whereas cellular isotropy, higher cell number density and greater longitudinal expansion were favored in the presence of pomace. A conceptual model for foaming and collapse was developed based on flow temperature of blends (123.7–167.6°C), specific mechanical energy, and anticipated changes in visco-elasticity and extensibility of the high-fiber melt. Cell size was significantly correlated to average crushing force (r=−0.69), crispness work (r=−0.69) and number of spatial ruptures (r=0.74). Microstructure data in combination with standard theory for brittle foams was employed to understand mechanical properties of extrudates under compression.

Use of non-invasive X-ray microtomography for characterizing microstructure of extruded biopolymer foams

Understanding foam microstructure formation is important for a priori design and engineering of new biopolymer-based products for both food and industrial applications. However, this has been hindered by unavailability of an imaging technology to characterize the cellular structure of foams accurately. This study investigated a non-invasive imaging technology, X-ray microtomography (XMT), for visualization and measurement of microstructural features of biopolymer foams. Brittle corn starch foams with two levels (5% and 15%) of whey protein concentrate (34% protein) factorialized with two moisture contents (26% or 34%) were produced using extrusion. XMT allowed non-invasive imaging of sample cross-sections at various depths, and facilitated accurate and hitherto impossible measurements of features like true cell size distribution (bi-modal), average diameter (0.58 to 2.27 mm), open wall area fraction (0.068 to 0.099), cell wall thickness (0.09 to 0.15 mm), and true void fraction (0.63 to 0.84). Results indicated XMT is superior to conventional imaging techniques for characterizing foam microstructure.

Bone formation during forelimb regeneration: a microtomography (microCT) analysis.

In our study of bone regeneration in the forelimbs of mature newts (Notophthalmus viridescens), we used noninvasive X-ray microtomography (microCT) to image regenerating limbs from 37 to 85 days and matching (contralateral) controls. We compared the patterns of regenerated and existing (nonregenerated) bone, investigating in particular the onset of mineralization of specific bones, the level of mineral present, and the lengths of the different bones. Overall, we find that the missing limb skeletal elements are restored in a proximal-to-distal direction, which reiterates the developmental patterning program. However, in contrast to this proximal-distal sequence, the portion of the humerus distal to the amputation site fails to ossify in synchrony with the regenerating radius and ulna. This finding suggests that the replacement of cartilage with mineralized bone close to the amputation site is delayed with respect to other regenerating skeletal elements.