Quality of micro-CT images acquired from simultaneous micro-CT and benchtop x-ray fluorescence computed tomography (XFCT): A preliminary Monte Carlo study

Integration of micro-CT with benchtop x-ray fluorescence computed tomography (XFCT) for multimodal imaging poses challenges due to significantly different operating conditions between the two modalities. This Monte Carlo (MC) study investigated the quality of micro-CT images obtainable with incident x-ray spectra that were optimized for benchtop XFCT and, consequently, considerably harder than those typically used for micro-CT. An MC model was created in MCNP5, featuring a cylindrical polymethyl methacrylate phantom (3-cm-diameter) with cylindrical inserts (6-mm-diameter) containing water loaded with gold nanoparticles (2, 1, and 0.5% by weight). The phantom was irradiated by a polychromatic cone-beam x-ray source operated at various tube potentials and filtration. Transmitted photons were scored while the phantom was rotated to generate projections for axial image reconstruction. Reconstructed micro-CT images were comparable to experimentally-obtained images under similar imaging conditions. For a given dose, the contrast and image quality generally decreased with increasing hardness of the incident xray spectrum. The results suggest that it would be difficult to achieve the contrast typical of micro-CT images with incident x-ray spectra optimized for benchtop cone-beam XFCT. Further optimization efforts and/or developing alternative imaging schemes (e.g., dualenergy scan) will be necessary to improve micro-CT image quality during simultaneous micro-CT/XFCT scanning.