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 x-ray 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., dual-energy scan) will be necessary to improve micro-CT image quality during simultaneous micro-CT/XF'CT scanning.