Comparison of Bone Mineral Density in Children and Adolescents on CT Versus DEXA Scan

Study Design. Retrospective cross-sectional. Objectives. To determine associations between Hounsfield units (HU) within a region of interest on computed tomography (CT) scans and dual energy X-ray absorptiometry (DEXA) measurements in children and adolescents. Summary of Background Data. HU on CT scans as a proxy for bone mineral density (BMD) is widely used in adults. However, the utility of CT as a proxy for BMD have not been evaluated in children and adolescents. Materials and Methods. Patients younger than 18 years with a lumbar spine CT scan and a DEXA within 6 months of each other were identified. A region of interest was used to measure the HU at each lumbar vertebral body on midaxial cuts. Charts were reviewed for demographics, medical comorbidities, and DEXA reports. Correlation coefficients were calculated between the mean DEXA Z-score and the HU value. Patients were also stratified by Z-score (>= -1.0, between -1.0 and -2.0, and <=-2.0) and matched by age, sex and body mass index (BMI) to a cohort of healthy children and compared. Results. A moderate correlation between mean DEXA Z-score and mean HU on CT was found (r(2)=0.42, P<0.001). After matching for age, sex and BMI, 21 patients in each group between the ages of 4 and 17 years were analyzed. The mean HU value of the control group was 231.69. When stratified by Z-score (>= -1.0, between -1.0 and -2.0, and <=-2.0), the mean HU values were 244.59, 216.50, and 176.54, respectively. Patients with a Z-score of <=-2.0 had a significantly lower mean HU than matched controls. Conclusions. HU on lumbar CT in children and adolescents with DEXA Z-scores <-2.0, were lower when compared with healthy matched controls. This study suggests that HU on opportunistic CT scans of the spine may be used as a reasonable proxy for BMD in the pediatric population.