Projection-Volume Hybrid Stitching for Large-Scale Synchrotron CT using a Vertical Fan-Beam Geometry

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Abstract
This study presents a practicable reconstruction workflow for cm-scale samples at the beamline BL05XU of SPring-8, utilizing a one-dimensional reflective beam expander (RBE) to expand the vertical field of view (FOV). While the original vertical beam size was limited to 1.3 mm, the RBE broadened it to approximately 5.7mm, enabling a massive 36 x 17 tiled scan of a smartphone in 15.5 hours. To handle the resulting geometry, we developed a hybrid reconstruction process: horizontal stitching in the projection domain followed by vertical stacking of reconstructed sub-volumes. We demonstrate that while a parallel-beam approximation is sufficient near the axis of rotation (AoR), it induces severe artifacts in regions distant from the AoR. Incorporating the RBE’s vertical fan-beam geometry is essential for high-fidelity large-scale imaging, effectively reducing artifacts that occur under a parallel-beam approximation.