The utility of photon-counting CT localizer radiograph in bone densitometry

Osteoporosis is a prevalent but underdiagnosed condition that significantly increases fracture risk, leading to substantial healthcare costs. Dual-energy X-ray absorptiometry (DEXA) remains the gold standard for areal bone mineral density (aBMD) assessment but is underutilized, with many at-risk individuals not undergoing screening. Photon-counting CT (PCCT) spectral localizer radiographs (LRs) offer a promising alternative for opportunistic osteoporosis screening by leveraging material decomposition to estimate areal BMD (aBMD) with a low radiation dose comparable to DEXA. This study evaluates the accuracy of PCCT spectral LRs for aBMD assessment through a combination of physical phantom experiments and virtual imaging human trials (VITs). Using a custom material decomposition algorithm, hydroxyapatite and water maps were generated from dual-energy spectral LRs to compute aBMD. Phantom measurements demonstrated strong agreement between PCCT-derived aBMD and DEXA values, with percentage differences ranging from 1.7% to 4.1%. VITs further optimized imaging parameters by varying mAs levels, revealing a reduction in mean absolute error from 0.2023 g/cm² at 35 mAs to 0.0863 g/cm² at 160 mAs, indicating improved measurement precision at higher exposure settings. These findings support the feasibility of PCCT spectral LRs for accurate, low-dose osteoporosis screening, potentially enabling early detection and reducing fracture-related healthcare burdens.