A multi-scan refinement technique combining cone-beam tomography and laminography

Abstract

In a fine-focus geometry, for a given detector, the resolution achievable by conventional tomographic region-of-interest (ROI) imaging is limited by the smallest possible distance of the radiation source from the rotation axis, i.e., the radius of the smallest cylinder about the rotation axis that encloses the object. In situations where the specimen to be imaged is irregularly shaped, or the ROI is off-centre, higher magnification can only be achieved from a limited range of angles, (possibly in a separate scan), and a tomographic reconstruction technique able to incorporate this additional data would be advantageous. Here we present such a technique for imaging planar (or laminar) objects based on a combination of multiple tomography and laminography scans with increasing magnification that employ helical and planar source trajectories respectively. Relative to laminography, this hierarchical combination improves depth resolution, (longitudinal direction), as well as reducing imaging artefacts. Relative to full-field tomography the proposed method increases resolution, particularly in the plane of the specimen, (transverse direction). The foundation of the technique is a generalisation of accelerated multi-grid tomographic reconstruction methods to the case of multiple independent collections of radiographs. Here we first demonstrate the concepts and performance of this technique through a simulated example. We then demonstrate the successful application of the method experimentally to a thin rock section and a printed circuit board.