Diagnostic Performance of Low-Dose Chest Photon-counting Detector CT for Assessing Lumbar Osteoporosis

Purpose To investigate the diagnostic performance of virtual calcium imaging (VCI) parameters from photon-counting detector (PCD) CT for assessing lumbar vertebral osteoporosis. Materials and Methods A phantom study was first conducted using standard- and low-dose PCD CT to assess the stability and reproducibility of VCI parameters. Participants who underwent dual-energy x-ray absorptiometry (DXA), the reference standard for osteoporosis assessment, and standard- or low-dose PCD CT were prospectively enrolled. Partial correlation coefficients were used to assess associations between VCI parameters and DXA-derived T-scores. Measurements were obtained from anterior, middle, and posterior vertebral subregions. Diagnostic performance for osteoporosis was evaluated using receiver operating characteristic analysis. Results In the phantom study, VCI parameters from standard- and low-dose PCD CT showed strong positive correlations with known bone density (r = 0.94-0.95; P < .001). A total of 94 participants (mean age, 69.82 years ± 9.39 [SD]; 55 female) in the low-dose group and 91 participants (mean age, 69.52 years ± 9.32; 53 female) in the standard-dose group were included in the analysis. In the low-dose group, CT attenuation for calcium (Cal), calcium density, and virtual monoenergetic 70 keV (ME70) attenuation values were significantly correlated with T-scores after adjustment for sex and body mass index (r = 0.64, 0.67, and 0.62, respectively; all P < .001). These parameters differed significantly across vertebral subregions and bone mass categories (normal, reduced, and osteoporosis; P < .001). Using thresholds of Cal of 133.70 HU or less, calcium density of 4.93 mg/cm³ or less, and ME70 of 112.43 HU or less, receiver operating characteristic analysis demonstrated good diagnostic performance for osteoporosis (areas under the receiver operating characteristic curve, 0.90, 0.91, and 0.89, respectively), with sensitivities of 85%, 87%, and 82% and specificities of 83%, 79%, and 84%, respectively. Similar results were observed in the standard-dose group. Conclusion VCI parameters from PCD CT showed strong correlations with DXA T-scores and demonstrated high diagnostic performance for osteoporosis, suggesting a promising opportunistic screening tool for lumbar vertebral bone density assessment. Keywords: CT Photon Counting, CT Dual Energy, Thorax, Spine Supplemental material is available for this article. © RSNA, 2026.