Iterative reconstruction optimisations for high angle cone-beam micro-CT

We address several acquisition questions that have arisen for the high cone-angle helical-scanning micro-CT facility developed at the Australian National University. These challenges are generally known in medical and industrial cone-beam scanners but can be neglected in these systems. For our large datasets, with more than 2048³ voxels, minimising the number of operations (or iterations) is crucial. Large cone-angles enable high signal-to-noise ratio imaging and a large helical pitch to be used. This introduces two challenges: (i) non-uniform resolution throughout the reconstruction, (ii) over-scan beyond the region-of-interest significantly increases required reconstructed volume size. Challenge (i) can be addressed by using a double-helix or lower pitch helix but both solutions slow down iterations. Challenge (ii) can also be improved by using a lower pitch helix but results in more projections slowing down iterations. This may be overcome using less projections per revolution but leads to more iterations required. Here we assume a given total time for acquisition and a given reconstruction technique (SART) and seek to identify the optimal trajectory and number of projections per revolution in order to produce the best tomogram, minimise reconstruction time required, and minimise memory requirements

Investigation on reconstruction methods applied to 3D terahertz computed tomography

International audience3D terahertz computed tomography has been performed using a monochromatic millimeter wave imaging system coupled with an infrared temperature sensor. Three different reconstruction methods (standard back-projection algorithm and two iterative analysis) have been compared in order to reconstruct large size 3D objects. The quality (intensity, contrast and geometric preservation) of reconstructed cross-sectional images has been discussed together with the optimization of the number of projections. Final demonstration to real-life 3D objects has been processed to illustrate the potential of the reconstruction methods for applied terahertz tomography

Data processing in a tomographic imaging apparatus

A method of investigating a specimen using a tomographic imaging apparatus , by performing , in multiple iterations , the following steps : ( i ) Using a Back Projection technique to produce an initial tomogram from a set of initial images ; ( ii ) Subjecting said initial tomogram to a mathematical filtering operation , thereby producing an adjusted tomogram ; ( iii ) Using a Forward Projection technique on said adjusted tomogram to dissociate it into a set of calcu lated images ; ( iv ) Repeating steps ( i ) - ( iii ) until said calculated images satisfy an acceptance criterion

X-ray versus 3D terabertz imaging for sigillograpby science

no abstrac

Acquisition and processing of data in a tomographic imaging apparatus

A method of investigating a specimen using a tomographic imaging apparatus using a stage for producing relative motion of a source with respect to a specimen , so as to allow the source and a detector to image the specimen along a series of different viewing axes and a processing apparatus for assembling a tomographic image of at least part of the specimen . The investigation is carried out by considering a virtual reference surface that surrounds the specimen and is substantially centered thereon , considering an incoming point of intersection of each of said viewing axes with this reference surface , thereby generating a set of such intersec tion points corresponding to the series of viewing axes , choosing discrete viewing axes in the series so as to cause the set to comprise a two - dimensional lattice of points located areally on the reference surface in a substantially uniform distribution

3D millimeter waves Tomosynthesis for the control of aeronautics materials

International audienc

Towards a 3D material characterization using dual-energy THz tomography

Terahertz (THz) tomography is a recent imaging technique allowing 3D inspection of opaque objects. In this paper, we investigate a dual-energy experimental setup and a THz tomographic reconstruction algorithm based on dual-energy measurements. We discus

Liquid index matching for 2D and 3D terahertz imaging

International audienceTwo-dimensional (2D) terahertz imaging and 3D visualization suffer from severe artifacts since an important part of the terahertz beam is reflected, diffracted, and refracted at each interface. These phenomena are due to refractive index mismatch and reflection in the case of non-orthogonal incidence. This paper proposes an experimental procedure that reduces these deleterious optical refraction effects for a cylinder and a prism made with polyethyl-ene material. We inserted these samples in a low absorption liquid medium to match the sample index. We then replaced the surrounding air with a liquid with an optimized refractive index, with respect to the samples being studied. Using this approach we could more accurately recover the original sample shape by time-of-flight tomography

X-ray versus 3D terabertz imaging for sigillograpby science

no abstrac

Investigation on reconstruction methods applied to 3D terahertz computed tomography

3D terahertz computed tomography has been performed using a monochromatic millimeter wave imaging system coupled with an infrared temperature sensor. Three different reconstruction methods (standard back-projection algorithm and two iterative analysis) have been compared in order to reconstruct large size 3D objects. The quality (intensity, contrast and geometric preservation) of reconstructed cross-sectional images has been discussed together with the optimization of the number of projections. Final demonstration to real-life 3D objects has been processed to illustrate the potential of the reconstruction methods for applied terahertz tomography