The reliability of measuring the density of the L1 vertebral body on CT imaging as a predictor of bone mineral density

Aim: To determine whether the density of the L1 vertebra measured on computed tomography (CT) images correlates with the bone mineral density (BMD) as measured by quantitative computed tomography (QCT), and to determine the reliability of L1 density measurements by different observers to see if this measure could help identify patients who would benefit from formal BMD assessment.

Materials and methods: Non-contrast CT along with a phantom for determination of BMD was performed on 30 healthy patients. The L1 density was measured by 3 observers at two time-points separated by at least 2 weeks.

Results: L1 density was well correlated to the QCT BMD (correlation coefficient 0.83; 95% confidence interval [CI]: 0.67-0.92). There was excellent intra- and interobserver agreement in L1 density measurements. There were excellent intra-class correlation coefficients for each observer's measurements at two separate time points with a coefficient for observer 1 of 0.94 (95% CI: 0.88-0.97) and for observer 2 and 3 of 0.99 (95% CI: 0.98-1). The interobserver measurements had an intra-class correlation coefficient of 0.98 (95% CI: 0.96-0.99).

Conclusion: L1 vertebral density can be reliably measured on CT images and might be used as an indicator of BMD for opportunistic screening of patients with osteoporosis. Low bone density detected incidentally on CT imaging could be used to identify patients who should be further investigated and treated for osteoporosis.