Opportunistic osteoporosis assessment from routine CT—effect of intravenous contrast agents on absolute values, T-scores, and derived classifications in single- and dual-energy CT

OBJECTIVES: Computed tomography (CT) is widely used for bone health assessment, impacting osteoporosis diagnosis and treatment. However, the influence of intravenous contrast agents on CT-based bone mineral density (BMD) measurements remains debated. This study evaluates the effect of contrast agents on Hounsfield measurements, T-scores, and Z-scores, assessing their impact on diagnostic accuracy to reduce misclassification and optimize CT-based BMD assessment. MATERIALS AND METHODS: A retrospective analysis of 597 patients (median age: 66 years, 157 females, 440 males) was performed using dual-energy CT (DECT) scans of the abdomen and chest. All patients underwent non-contrast, arterial, and venous phase CT. Automated segmentation (nnU-Net) delineated L1 and L1-L4 trabecular bone, validated by two radiologists. T-scores were calculated according to DEXA-equivalent guidelines. RESULTS: Based on non-contrast CT, 35% were diagnosed with osteoporosis, 46% with osteopenia, and 18% had normal bone status. Median T-score was -2.0 (L1) and -2.1 (L1-L4) (p < 0.001). Contrast agents significantly altered BMD values, with median changes of 22.9% (arterial) and 20.1% (venous). The most pronounced changes occurred in patients under 50 years (+99% at L1, p < 0.001). In older females, 21% were misclassified as osteopenic instead of osteoporotic (p < 0.001). CONCLUSIONS: Contrast agents significantly affect BMD measurements, leading to diagnostic misclassification. This effect should be considered when using CT for osteoporosis diagnosis and treatment planning. KEY POINTS: Question Standard CT scans with contrast media may distort bone density measurements, potentially leading to misdiagnosis of osteoporosis and inappropriate clinical decisions. Findings Contrast-enhanced CT scans significantly alter T- and Z-scores, leading to diagnostic shifts in over 50% of patients, especially women over 50. Clinical relevance Our findings highlight the risk of osteoporosis misclassification due to contrast agents in CT imaging, underscoring the need for adjusted interpretation protocols to ensure accurate diagnosis and appropriate treatment, particularly in older adults and female patients.