In vivo imaging of cortical porosity by synchrotron phase contrast micro computed tomography

Cortical bone is a dynamic tissue which undergoes adaptive and pathological changes throughout life. An improved understanding of the spatio-temporal process of remodeling holds great promise for improving our understanding of bone development, maintenance and senescence. The use of micro-computed tomography (µCT) on living animals is relatively new and allows the three dimensional quantification of change in trabecular bone microarchitecture over time. The use of in vivo µCT is limited by the radiation dose created by the x-ray beam, with commercially available in vivo systems generally operating in the 10-20 um resolution range and delivering an absorbed dose between 0.5-1 Gy. Because dose scales to the power of four with resolution, in vivo imaging of the cortical canal network, which requires a higher resolution, has not been achieved. I hypothesized that using synchrotron propagation phase contrast µCT, cortical porosity could be imaged in vivo in rats at a dose on the same level as those used currently for trabecular bone analysis. Using the BMIT-BM beamline, I determined the optimal propagation distance and used ion chamber and lithium fluoride crystal thermoluminescent dosimetry to measure the absorbed dose of my in vivo protocol as well as several ex vivo protocols using synchrotron phase contrast µCT at 5 µm, 10 µm, and 11.8 µm and conventional desktop in vivo protocols using commercial µCT systems. Using synchrotron propagation phase contrast µCT, I scanned the forelimb of two adult Sprague-Dawley rats and measured an absorbed dose of 2.53 Gy. Using two commercial µCT system, I measured doses between 1.2-3.6 Gy for protocols at 18µm that are in common use. This thesis represents the first in vivo imaging of rat cortical porosity and demonstrates that an 11.8 µm resolution is enough to visualize cortical porosity in rats, with a dose within the scope of those used for imaging trabecular bone in vivo

Superconducting tantalum disulfide nanotapes; growth, structure and stoichiometry

Superconducting tantalum disulfide nanowires have been synthesised by surface-assisted chemical vapour transport (SACVT) methods and their crystal structure, morphology and stoichiometry studied by powder X-ray diffraction (PXD), scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and nanodiffraction. The evolution of morphology, stoichiometry and structure of materials grown by SACVT methods in the Ta-S system with reaction temperature was investigated systematically. High-aspect-ratio, superconducting disulfide nanowires are produced at intermediate reaction temperatures (650 degrees C). The superconducting wires are single crystalline, adopt the 2H polytypic structure (hexagonal space group P6(3)/mmc: a = 3.32(2) angstrom, c = 12.159(2) angstrom; c/a = 3.66) and grow in the <2<(1)over bar>(1) over bar0> direction. The nanowires are of rectangular cross-section forming nanotapes composed of bundles of much smaller fibres that grow cooperatively. At lower reaction temperatures nanowires close to a composition of TaS3 are produced whereas elevated temperatures yield platelets of 1T TaS2

Absorption, refraction and scattering retrieval with an edge-illumination-based imaging setup

We have recently developed a new method based on edge-illumination for retrieving a three-image representation of the sample. A minimum of three intensity projections are required in order to retrieve the transmission, refraction and ultra-small-angle scattering properties of the sample. Here we show how the method can be adapted for particular cases in which some degree of a priori information about the sample might be available, limiting the number of required projections to two. Moreover, an iterative algorithm to correct for non-ideal optical elements is proposed and tested on numerical simulations, and finally validated on experimental data

Digital predictions of complex cylinder packed columns

A digital computational approach has been developed to simulate realistic structures of packed beds. The underlying principle of the method is digitisation of the particles and packing space, enabling the generation of realistic structures. Previous publications [Caulkin, R., Fairweather, M., Jia, X., Gopinathan, N., & Williams, R.A. (2006). An investigation of packed columns using a digital packing algorithm. Computers & Chemical Engineering, 30, 1178–1188; Caulkin, R., Ahmad, A., Fairweather, M., Jia, X., & Williams, R. A. (2007). An investigation of sphere packed shell-side columns using a digital packing algorithm. Computers & Chemical Engineering, 31, 1715–1724] have demonstrated the ability of the code in predicting the packing of spheres. For cylindrical particles, however, the original, random walk-based code proved less effective at predicting bed structure. In response to this, the algorithm has been modified to make use of collisions to guide particle movement in a way which does not sacrifice the advantage of simulation speed. Results of both the original and modified code are presented, with bulk and local voidage values compared with data derived by experimental methods. The results demonstrate that collisions and their impact on packing structure cannot be disregarded if realistic packing structures are to be obtained

Three dimensional characterization of tissue-engineered constructs by contrast enhanced nanofocus computed tomography.

peer reviewedIn order to successfully implement tissue engineered (TE) constructs as part of a clinical therapy, it is necessary to first develop and validate quality control tools that will ensure accurate and consistent TE construct release specifications. Hence advanced methods to monitor TE construct properties need to be further developed. In this study we showed proof of concept for contrast enhanced nanofocus computed tomography (CE-nanoCT) as a 'whole-construct' imaging technique with non-invasive potential that enables 3D visualization and quantification of in vitro engineered extracellular matrix (ECM) in TE constructs. In particular we performed a 3D quantitative and qualitative structural and spatial assessment of the in vitro engineered ECM, formed during static and perfusion bioreactor cell culture in 3D TE scaffolds, using two contrast agents, namely Hexabrix(R) and phosphotungstic acid (PTA). CE-nanoCT image data were validated by comparison to Live/Dead viability/cytotoxicity and picrosirius red staining data, and to the net dry weight of the TE constructs. When using Hexabrix(R) as contrast agent, ECM volume fitted linearly with net dry ECM weight independent from the flow rate used. When using PTA as contrast agent, CE-nanoCT data showed pronounced distinction between flow conditions when compared to both net dry weight and picrosirius red staining data although linearity was maintained, indicating culture-specific structural ECM differences. This was attributed to the binding specificity of this contrast agent. This novel type of information can contribute to optimize bioreactor culture conditions and potentially critical quality characteristics of TE constructs such as ECM quantity and homogeneity, facilitating the gradual transformation of 'TE constructs' in well characterized 'TE products'.I.P. is funded by the ENDEAVOUR project G.0982.11N of the FWO;M.S. is supported by a Ph.D. grant of the Agency for Innovation by Science and Technology (IWT/111457). G.K. and L.G. acknowledge support by the European Research Council under the European Union's Seventh Framework Program (FP7/2007–2013)/ERC grant agreement n°279100

Visualising and modelling flow processes in fractured carbonate rocks with X-ray computed tomography

Naturally Fractured Reservoirs (NFR) have typically very complex geometries from the pore scale to the field scale – discontinuities can be found at each scale. This makes NFRs hard to accurately be modelled for flow simulations. Fractures are especially difficult to incorporate in the simulations. The topology of a single fracture is usually simplified to a plane or disk, and apertures are usually averaged to be implemented in the simulation models. The fracture aperture distribution of a single fracture is already very heterogeneous though. Contact areas in fractures can detain flow, whereas connected fracture regions with larger apertures can result in preferred flow paths and lead to early breakthrough. To help understanding how well current Discrete Fracture and Matrix (DFM) models are suitable to retain fracture influences on flow in carbonates, this research project combines the simulation of miscible single-phase flow through fractures in carbonates with precise fracture measurements (comprising fracture aperture distributions and 3D topologies) and the visualization of real single and two-phase flow experiments in fractured carbonate cores. The simulation approach employs a DFM model with a hybrid finite element/ finite volume (FEFV) method. The fractured core samples and the flow experiments are imaged with high-resolution X-ray computer tomography (CT), or X-ray radiography respectively. The main goals are to develop and optimize an image processing workflow from the X-ray CT fracture measurement to an according mesh generation as input for simulations, and to be able to compare simulations and flow experiment studies qualitatively to analyse how well the DFM approach is able to capture the true nature of fluid flow in fractures with real aperture distributions. To obtain most relevant comparisons, we conduct numerical simulations and flow experiments on the same fracture geometries, which have been measured before non-destructivel