Measurement of Thoracic Bone Mineral Density with Quantitative CT

Purpose: To create standard thoracic bone mineral density (BMD) values for patients undergoing cardiac computed tomography (CT) by using thoracic quantitative CT and to compare these BMDs (in a subpopulation) with those obtained by using lumbar spine quantitative CT. Materials and Methods: The institutional review board approved this HIPAA-compliant study. A total of 9585 asymptomatic subjects (mean age, 56 years; age range, 30-90 years) who underwent coronary artery calcium scanning, including 4131 women, were examined. Patients with vertebral deformities or fractures were excluded. Six hundred forty-four subjects (322 of whom were female) also underwent lumbar quantitative CT. The mean thoracic vertebral BMDs for both sexes were reported separately in a subgroup of subjects aged 30 years and in 29 age-based subgroups in 2-year intervals from ages 30 to 90 years. The formulas used to calculate the female T score (T-f) and the male T score (T-m) on the basis of thoracic quantitative CT measurements were as follows: T-f = (BMDim 2 222)/36, and T-m = (BMDim 2 215)/33, where BMDim is the individual mean BMD. Comparisons between thoracic quantitative CT and lumbar quantitative CT measurements, as well as analyses of intraobserver, interobserver, and interscan variability, were performed. Results: The young-subgroup mean BMD was 221.9 mg/mL +/- 36.2 (standard deviation) for the female subjects and 215.2 mg/mL +/- 33.2 for the male subjects. The mean thoracic BMDs for the female and male subjects were found to be 20.7% higher and 17.0% higher, respectively, than the values measured with lumbar quantitative CT (P < .001 for both comparisons). A significant positive association between the thoracic and lumbar quantitative CT measurements (r. > 0.85, P < .001) was found. Intraobserver, interobserver, and interscan variabilities in thoracic quantitative CT measurements were 2.5%, 2.6%, and 2.8%, respectively. Conclusion: There was a significant association between the mean thoracic and lumbar BMDs. Therefore, standard derived measurements (young-subgroup BMD 6 standard deviation) based on these data can be used with thoracic CT images to estimate the bone mineral status. (C) RSNA, 2010