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

Abstract

Study Design. Retrospective cross-sectional Objectives. To determine associations between Hounsfield Units (HU) within a Region of interest (ROI) on 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. Methods. Patients younger than 18 years with a lumbar spine CT scan and a DEXA within 6 months of each other were identified. A ROI was used to measure the HU at each lumbar vertebral body on mid-axial cuts. Charts were reviewed for demographics, medical co-morbidities and DEXA reports. Correlation coefficients were calculated between mean DEXA Z-score and HU value. Patients were also stratified by Z-score (≥ −1.0, between −1.0 and −2.0, and ≤−2.0) and matched by age and 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 (r2=0.42, P<0.001). After matching for age and BMI, 21 patients in each group between the age 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 age matched controls. Conclusions. HU on lumbar CT in children and adolescents with DEXA Z-scores less than −2.0, were lower when compared to healthy age and BMI 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.