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

Abstract

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