Multi-Energy Blended CBCT Spectral Imaging Using a Spectral Modulator with Flying Focal Spot (SMFFS)

Abstract

Cone-beam CT (CBCT) spectral imaging has great potential in medical and industrial applications, but it is very challenging as scatter and spectral effects are seriously twisted. In this work, we present the first attempt to develop a stationary spectral modulator with flying focal spot (SMFFS) technology as a promising, low-cost approach to accurately solving the X-ray scattering problem and physically enabling spectral imaging in a unified framework, and with no significant misalignment in data sampling of spectral projections. Based on an in-depth analysis of optimal energy separation from different combinations of modulator materials and thicknesses, we present a practical design of a mixed two-dimensional spectral modulator that can generate multi-energy blended CBCT spectral projections. To deal with the twisted scatter-spectral challenge, we propose a novel scatter-decoupled material decomposition (SDMD) method by taking advantage of a scatter similarity in SMFFS. A Monte Carlo simulation is conducted to validate the strong similarity of X-ray scatter distributions across the flying focal spot positions. Both numerical simulations using a clinical abdominal CT dataset, and physics experiments on a tabletop CBCT system using a GAMMEX multi-energy CT phantom, are carried out to demonstrate the feasibility of our proposed SDMD method for CBCT spectral imaging with SMFFS. In the physics experiments, the mean relative errors in selected ROI for virtual monochromatic image (VMI) are 0.9\% for SMFFS, and 5.3\% and 16.9\% for 80/120 kV dual-energy cone-beam scan with and without scatter correction, respectively. Our preliminary results show that SMFFS can effectively improve the quantitative imaging performance of CBCT.Comment: 10 pages, 13 figure