Technical considerations for fan-beam dual-energy x-ray absorptiometry body composition measurements in pediatric studies

BACKGROUND: A piglet model was used to determine the influence of frequently encountered situations in clinical studies of infants and young children on fan-beam dual-energy x-ray absorptiometry (DXA) measurements. METHODS: DXA scans of piglets (640 g to 21,100 g) were acquired in the infant and adult mode and were analyzed with 1 infant, 1 pediatric, and 3 versions of adult software. RESULTS: The effect of repositioning of the piglets from the center to the periphery of the scanning table on DXA measurements included an average difference of up to 0.5% for total weight, 5.0% for bone mineral content, 5.6% for bone mineral density, 1.3% for lean mass, and 21.9% for fat mass (< or = .05, all comparisons) although no significant changes occurred when the piglets were scanned in symmetrical positions on either edge of the scanning table. Different posture (prone vs supine and side), varied number of blankets overlaid or wrapped around the piglet, and parenteral but not enteral bolus feeding could significantly alter fan-beam DXA measurements to varying extents. Adult and pediatric software underestimated bone area and bone mineral content but overestimated bone mineral density, lean mass, fat mass, and total weight compared with infant software measurements. However, strong predictive relationships among these fan-beam DXA data in subjects >10 kg allow systematic corrections of data from different scan modes and different software. CONCLUSIONS: Attention to details and consistency in the technique for scan acquisition and analysis are critical to the generation of meaningful data and to allow for detection of true differences in DXA measurements of small subjects.