Diagnostic accuracy of axial and sagittal CT measurements for osteoporosis: A multi-vertebra evaluation

Background: This study aims to assess the diagnostic accuracy of axial and sagittal CT-derived Hounsfield Unit (HU) values in identifying osteopenia and osteoporosis. Additionally, it investigates whether the combination of multiple vertebral levels enhances predictive performance compared to single-level assessments.

Methodology: This retrospective study included 346 patients from who underwent both dual-energy X-ray absorptiometry (DXA) and non-contrast thoracic computed tomography (CT) scans within a 6-month interval. Axial and sagittal HU measurements were obtained from key vertebral levels, including T4, T7, T10, T12, and L1. Logistic regression and receiver operating characteristic (ROC) analyses were performed to evaluate the diagnostic performance of individual and combined vertebral models. Patients with vertebral metastases, hemangiomas, compression fractures, or severe deformities were excluded.

Results: The sagittal T4 vertebra measurement achieved the highest individual AUC (0.810), indicating strong diagnostic potential. Combining T4 and L1 measurements improved the AUC to 0.828, while a six-vertebra model yielded a slightly higher AUC of 0.844. Despite this marginal improvement, simpler two-vertebra models offer practical advantages in clinical settings. Optimal cut-off values were determined using Youden’s Index, with T4S at 164 HU and L1S at 133 HU, both showing high specificity but moderate sensitivity.

Conclusions: Axial and sagittal CT measurements, particularly at T4 and L1 levels, demonstrate strong potential for diagnosing osteopenia and osteoporosis. Combining multiple vertebral levels offers improved predictive accuracy, although simpler models remain effective. Opportunistic CT screening, utilizing scans performed for other clinical purposes, provides a practical and cost-effective alternative to DXA, enabling early intervention and comprehensive osteoporosis management.