Optical CT imaging of solid radiochromic dosimeters in mismatched refractive index solutions using a scanning laser and large area detector

摘要: Purpose: The practical use of the PRESAGE® solid plastic dosimeter is limited by inconvenience immersing it in high-viscosity oils to achieve refractive index matching for optical computed tomography (CT) scanning. The are slow mix and difficult clean from surfaces, rotation can generate dynamic Schlieren inhomogeneity patterns reference liquid, limiting rotational overall scan speed. Therefore, would be beneficial if lower-viscosity, water-based solutions with slightly unmatched could used instead. purpose this work demonstrate feasibility allowing mismatched conditions when using a scanning laser system large acceptance angle detector. A fiducial-based ray path measurement technique combined an iterative CT reconstruction algorithm reconstruct images. Methods: A water based surrounding liquid low viscosity was selected imaging dosimeters. Liquid selection optimized as high possible while avoiding rotation-induced effects. This led mismatch 6% between Optical scans were performed fan-beam scanning-laser area detector capture most refracted rays. fiducial marker placed on wall cylindrical sample occludes given light twice. With knowledge radius object, actual internal each through calculated. Scans 1024 projections 512 data samples each, rays rebinned form parallel-beam projections. Reconstructions × grid 100 iterations SIRT algorithm. Proof concept demonstrated uniformly attenuating solution phantom. dosimeters (11 cm diameter) irradiated Cobalt-60 irradiator either uniform dose or 2-level “step-dose” pattern. Results: With mismatching, circular field view 85% diameter reconstructed accurately. Reconstructed images test phantom (within 3%) inside radius. However, responses not spatially uniform, variations at least 5% sensitivity. variation appears “cupping” artifact less sensitivity middle than periphery cylinder. Polarization effects also detected these samples. Conclusions: The scheme, coupled algorithm, enabled immersed solutions. improvements response uniformity required.