Standardizing Attenuation across Tube Voltages and Vertebral Levels for Opportunistic Osteoporosis Screening on Low-dose Chest CT

Background Opportunistic screening of osteoporosis on CT has emerged as a cost-effective strategy for bone health assessment. However, vertebral attenuation varies substantially with CT tube voltage and spinal level, limiting standardization. Purpose To model and standardize vertebral attenuation across tube voltages and spinal levels on low-dose chest CT for opportunistic osteoporosis screening. Materials and Methods This retrospective study included 589 patients (336 women; mean age ± standard deviation, 65.9 ± 12.4 years) who underwent two non-contrast low-dose chest CT examinations and one dual-energy X-ray absorptiometry (DXA) within 3 months. Vertebral attenuation was measured at T10–L2 on CT using a deep learning-based software (AVIEW SpineBH, Coreline Soft). Osteoporosis was diagnosed using DXA. A linear mixed-effects model regressed attenuation on the logarithm of tube voltage, incorporating fixed effects for spinal level (T10–L2) and patient-specific random effects. Model performance was evaluated by converting the L1–120 kVp reference to other tube-voltage–level combinations and comparing predicted with observed attenuation using Pearson correlation, mean bias, and 95% limits of agreement. Diagnostic applicability was assessed by comparing receiver operating characteristic (ROC)–derived thresholds with model-predicted thresholds converted from the reference. Results Vertebral attenuation decreased by approximately 6–11 HU for every 10-kVp increase (β = −88.8 HU per log[kVp]; P < 0.001), and declined by approximately 4–14 HU per level from T10 to L2. Predicted values closely matched observed measurements (r = 0.89; mean bias, 2.2 HU; 95% limits of agreement, –54 to 59 HU). The model-predicted thresholds showed strong agreement with ROC-derived thresholds, differing by 1–10 HU across tube voltages and spinal levels. Conclusion A log-linear mixed-effects model enables population-level standardization of vertebral attenuation across tube voltages and spinal levels, supporting the development of more consistent opportunistic CT-based osteoporosis screening methods on non-contrast chest CT.