Osteoporosis is a progressive disease characterized by low bone mass and structural deterioration of bone tissue, leading to increased fragility and fracture risk. Globally, osteoporosis constitutes a significant public health issue, with projections indicating a substantial rise in its incidence and associated fractures, particularly among aging populations.1

Dual-energy X-ray absorptiometry (DXA) is widely recognized as the gold standard for diagnosing osteoporosis. However, its sensitivity can be limited, especially in patients with vertebral deformities, compression fractures, or spinal instrumentation. Furthermore, many at-risk patients remain undiagnosed or untreated, leading to preventable complications and healthcare costs.2

Recently, the use of computed tomography (CT) for opportunistic screening of bone mineral density (BMD) has gained traction. CT offers volumetric measurements of bone density, which provide more detailed assessments than the planar measurements of DXA. In particular, CT-derived Hounsfield Unit (HU) values have been shown to correlate strongly with DXA-derived BMD scores and offer the added advantage of detecting vertebral compression fractures in routine clinical scans.3 This has led to the increasing use of CT scans, not only for their primary diagnostic purpose but also for opportunistic screening for osteoporosis and osteopenia in high-risk populations.

Previous studies have primarily focused on lumbar vertebrae for these evaluations.4,5 However, thoracic vertebrae, particularly those captured during routine thoracic imaging, offer an additional avenue for identifying at-risk individuals. Despite the advantages, the specific diagnostic contributions of axial versus sagittal measurements and the optimal combination of vertebral levels remain underexplored. Moreover, integrating both axial and sagittal measurements into diagnostic models may further improve the accuracy of osteoporosis screening.6

This study aims to assess the efficacy of axial and sagittal CT-derived HU values in distinguishing normal, osteopenic/osteoporotic individuals. By systematically comparing various vertebral levels, including combinations of axial and sagittal measurements, we seek to determine which vertebral measurements provide the highest diagnostic accuracy. The secondary objective is to evaluate whether using multiple vertebral levels enhances predictive performance compared to single-level assessments.