Qualitative comparison of several phase correction algorithms in single-image in-line X-ray phase contrast tomography

In recent years, phase contrast has gained importance in the field of X-ray imaging and more particular in high-resolution X-ray computed tomography or micro-CT. For phase propagation imaging, no additional hardware or specific setup is required, which makes the effect inherent to micro-CT where it is manifested as an edge-enhancement effect. As such, it can be beneficial for qualitative analysis of a 3D volume. Nevertheless, it induces unreal gray values and is thus often considered as an imaging artefact which hinders proper quantitative 3D analysis. Several methods exist to reduce this phase contrast effect or to retrieve the phase information from the mixed phase-and-amplitude images. In this presentation, a comparison will be made between 2 phase retrieval algorithms and 2 phase correction algorithms. Of these 2 latter, one can be performed on the reconstructed volume, which clearly facilitates the operation of phase correction

Understanding phase contrast artefacts in micro computed absorption tomography

Phase contrast imaging is a technique which captures objects with little or no light absorption. This is possible due to the wave nature of light, i.e., diffraction. In computerised tomography, the aim is most often to reconstruct the light absorption property of objects but many objects can not be imaged without obtaining a mix of both absorption and phase, this is especially true for weakly absorbing objects at high resolution. Hence, phase contrast is usually considered an unwanted artefact which should be removed. Traditionally this is done directly on the projection data prior to the filtered back projection algorithm and the filter settings are derived from the physical setup of the imaging device. In this paper we show how these operations can be carried out on the reconstructed data, without access to the projection images, which yields much flexibility over previous approaches. Especially, filtering can be applied to small regions of interest which simplifies fine tuning of parameters, and some low pass filtering can be avoided which is inherent in previous methods. We will also show the filter parameters can be estimated from step edges in the reconstructed images

DHXCT: the use of helical X-ray CT in dendro-research

X-ray Computed Tomography (XCT) has become a well-established technique in many fields of science. Its application in wood research is also increasing considerably. Thanks to the non-destructive nature of the imaging process as well as the internal view on the three-dimensional structure, it is one of the pre-eminent techniques for multi-scale studies of wood. With standard cone-beam tomography, however, long samples with limited cross-sectional dimensions are hard to scan at high resolution. Stacked scanning and volume stitching are necessary for such samples. Tree-ring research mainly uses increment cores or generally speaking pith-to-bark trajectories which are typically long but with rather small cross-sectional dimensions. Such samples, therefore, could benefit from other acquisition routines, such as the helical scanning protocol. The sample is not only rotated 360° but is also moved along the z-axis, resulting in a helical movement. We will show how helical X-CT (HXCT) can be of use in tree-ring research, giving examples of its use on oak (Quercus spp.), limba (Terminalia superba) and teak (Tectona grandis). Custom-made sample holders enable scanning of several pith-to-bark trajectories sawn from wood disks simultaneously. Reconstructed volumes can be converted to absolute densities without classical time-consuming calibration methods and density profiles can be obtained. Furthermore, the 3D volume can also be used for accurate ring width measurements taking into account ring and grain angle. In some cases, quantitative wood anatomical measurements are also feasible. Finally, dedicated scans at higher resolution can resolve finer anatomical details