Imaging system performing substantially exact reconstruction and using non-traditional trajectories

A method and apparatus for reconstruction of a region of interest (ROI) for an object using an imaging system is provided. The imaging system may substantially exactly reconstruct the ROI with a straight line trajectory. In the straight line trajectory, the ROI is not bounded or encircled by the actual trajectory of the source (e.g., no chords that are composed from two points on the source trajectory intersect or fill the ROI to be imaged). However, the ROI may be substantially reconstructed by using "virtual" chords to reconstruct the ROI. The virtual chords are such that no point on the trajectory is included in the virtual chord (such as one that is parallel to the straight line trajectory). These virtual chords may intersect and fill the ROI, thus enabling substantially exact reconstruction. Further, in reconstructing the image, the straight line trajectory may be assumed to be infinite in length

Correlative Tomography: Three Dimensional Multiscale Imaging and Modelling of Hierarchical Porous Materials

Heterogeneous catalyst based pellets typify a material where functionality is dependant on hierarchical pore structures spanning many orders of magnitude from nanometers up to tens of microns. The total activity, selectivity and lifetime of catalyst based pellets depends on the ability of molecules to flow through a large pellet bed (m), into the pellets (mm) and their pore structure (μm-nm) to/from the active sites. Three dimensional imaging techniques such as tomography allow for the direct characterisation and quantification of pore structures. However, the field of view in tomography decreases as resolution increases. This work circumvents this issue with multiscale tomography (MT) combining x-ray microtomography (XMT), dual beam focused ion beam tomography (DB-FIB) and electron tomography (ET) to probe porous pellet based catalysts. The results show MT as a viable method that offers new insights into the quantification and behaviour of pellet based catalysts across large length scales, all in three dimensions (3D), that no single tomographic technique can adequately capture. MT was successfully used in the characterising of pore sizes, distributions, structures and spatial relationships and this was compared to existing multiscale characterisation techniques to illustrate the new insights that can be obtained. The pore structures were meshed and modeled using MT data to provide results for understanding the transport properties scaled up from the nanometre length scale to the packed bed, through pellet based catalysts produced under different manufacturing conditions. The results show the very strong dependence on the calcining temperature which is important for designing better catalysts in future. The tomography data was also used to determine thermal/mechanical stresses at both a pellet and pellet bed level. Although many stresses are compressive; the packing of the pellets creates local tensile stresses and a potential cause for pellet failure through internal flaws at relatively low loads. In summary, multiscale tomography was demonstrated to be a viable method for obtaining new insights for the development of pellet based catalysts by both improved quantification and allows for the first time direct 3D multiscale simulation of transport and mechanical properties across multiple scales from nanometers to metres to catalyst pellets in beds

Extending Three-Dimensional Weighted Cone Beam Filtered Backprojection (CB-FBP) Algorithm for Image Reconstruction in Volumetric CT at Low Helical Pitches

A three-dimensional (3D) weighted helical cone beam filtered backprojection (CB-FBP) algorithm (namely, original 3D weighted helical CB-FBP algorithm) has already been proposed to reconstruct images from the projection data acquired along a helical trajectory in angular ranges up to [0,2π]. However, an overscan is usually employed in the clinic to reconstruct tomographic images with superior noise characteristics at the most challenging anatomic structures, such as head and spine, extremity imaging, and CT angiography as well. To obtain the most achievable noise characteristics or dose efficiency in a helical overscan, we extended the 3D weighted helical CB-FBP algorithm to handle helical pitches that are smaller than 1:1 (namely extended 3D weighted helical CB-FBP algorithm). By decomposing a helical over scan with an angular range of [0,2π+Δβ] into a union of full scans corresponding to an angular range of [0,2π], the extended 3D weighted function is a summation of all 3D weighting functions corresponding to each full scan. An experimental evaluation shows that the extended 3D weighted helical CB-FBP algorithm can improve noise characteristics or dose efficiency of the 3D weighted helical CB-FBP algorithm at a helical pitch smaller than 1:1, while its reconstruction accuracy and computational efficiency are maintained. It is believed that, such an efficient CB reconstruction algorithm that can provide superior noise characteristics or dose efficiency at low helical pitches may find its extensive applications in CT medical imaging