Interchangeability of pencil-beam and fan-beam dual-energy X-ray absorptiometry measurements in piglets and infants

Background: Compared with the older pencil-beam (PB) dual-energy X-ray absorptiometry (DXA), the newer fan-beam (FB) DXA has the advantage of faster scan acquisition and greater accuracy of body-composition measurement in small subjects. However, no data exist on the relation between the measurements obtained with these techniques. Objective: The objective of the study was to investigate whether PB and FB DXA measurements in small subjects are interchangeable. Design: PB and FB DXA scans were performed on 26 piglets and 54 infants to examine the relation between the measurements obtained by using the 2 techniques. Results: The correlation between all PB and FB DXA measurements of variables (total weight, bone area, bone mineral content, bone mineral density, and lean and fat masses) approached 1.0, but there were significant differences in absolute values. The extent of the differences varied according to the variable, with the lowest value for total weight (mean difference: ≈1% for both piglets and infants) and the highest value for bone mineral content (mean difference: 35.3% and 36.7% for piglets and infants, respectively). PB and FB DXA measurements were strongly predictive of each other after adjustment (r2 = 0.927–1.000 for the piglet data and 0.939–0.999 for the infant data). Conclusion: In small subjects, DXA measurements from PB and FB techniques were strongly predictive of each other, although their absolute values differed. Thus, group comparison of PB and FB DXA data is possible after adjustment of the data from either technique. It is advisable to generate normative data for each technique and to use the same technique throughout longitudinal studies.