Quantitative Cone-Beam CT with High-fidelity Modeling of Imaging Physics*

Bone mineral density (BMD) and bone microstructure are key biomarkers of orthopedic health. Quantitative assessment of these parameters requires high accuracy of reconstructed attenuation values and high spatial resolution. We employ advanced models of x-ray propagation to optimize performance of specialized orthopedic Cone-Beam CT systems in quantitative bone imaging. To achieve accurate measurements of BMD, a model-based reconstruction (MBR) framework utilizing polyenergetic spectral models is used in concert with fast Monte Carlo scatter correction. To advance spatial resolution to a level consistent with trabecular detail (~100 μm), we adopt a customized low-noise CMOS x-ray detector with 400 μm-thick scintillator, optimized through cascaded systems modeling of task-based imaging performance. Studies of BMD accuracy indicate that MBR is able to estimate CaCO₃ concentration with <20 mg/mL error, irrespective of object size and position. The use of optimized CMOS sensor yielded improved correlation with gold-standard micro-CT measurements of bone microstructure compared to current-generation flat-panel detector CBCT, e.g. correlation for trabecular thickness increased from 0.84 with a flat-panel CBCT to 0.96 with CMOS.