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 2 noncontrast low-dose chest CT examinations and 1 dual-energy X-ray absorptiometry 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 dual-energy X-ray absorptiometry. 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-derived thresholds with model-predicted thresholds converted from the reference. Results: Vertebral attenuation decreased by approximately 6-11 Hounsfield units (HU) for every 10-kVp increase (β = -88.8 HU per log[kVp]; Conclusions: 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 noncontrast chest CT.