The detail, feature resolution and speed benefits of phase contrast and synchrotron X-ray source 3D tomographic imaging of geomaterials over conventional laboratory X-CT
Ian J Corfe, Elis Newham, Pam Gill, Jukka Kuva, and Alan R Butcher
Three-dimensional X-ray Computed Micro- and Nano-tomography (Micro-/Nano-X-CT) is an increasingly important tool for characterising rock properties in fields such as hydrocarbon exploration, mining, and general geoscience. By allowing non-destructive, high resolution imaging of internal features, digital 3D models of features of interest can be measured through entire sample volumes, allowing a fuller understanding of their characteristics by comparison with 2D-only methods. However, since the method is based on differential absorption properties of materials within the sample, visible and digital separation of materials with weakly contrasting density, especially at fine-scale, is difficult. This is commonly the case with geomaterials of relatively homogenous composition, including clay-, quartz- and feldspar-bearing sedimentary rocks, olivine and pyroxene bearing igneous rocks, and the internal structures of originally hydroxy-apatite dominated fossils. Various phase contrast imaging methods, however, allow enhanced contrast between weakly differentiated materials, allowing them to be identified and processed as separate objects for characterisation and measurement. Some of these phase effects are available with laboratory X-ray source CT machines, and it can be worth exploring these if absorption image processing fails to give the desired results.
A second alternative to laboratory X-ray source CT absorption imaging is the use of a synchrotron X-Ray source. Synchrotron particle accelerators provide X-ray beams with high brilliance, meaning a high intensity/photon flux plus low beam divergence, and allow additional phase effects to be used. Synchrotron imaging typically provides a higher signal-to-noise ratio, and allows smaller feature identification for the same voxel size and faster scan times, than conventional X-CT imaging. By combining a synchrotron X-Ray source and phase contrast image processing, extremely low contrast difference features can be identified within geomaterials.
In this presentation, we discuss the advantages and disadvantages of these two extensions to conventional CT imaging, using case studies from fossil fragments, fossil-bearing sedimentary rocks, and limestones.
