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ARS Home » Plains Area » Houston, Texas » Children's Nutrition Research Center » Research » Publications at this Location » Publication #304530
Title: Solid anthropomorphic infant whole body DXA phantom: Design, evaluation, and multisite testing

Author
item SHYPAILO, ROMAN - Children'S Nutrition Research Center (CNRC)
item ELLIS, KEN - Children'S Nutrition Research Center (CNRC)

Submitted to: Pediatric Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/8/2013
Publication Date: 10/16/2013
Citation: Shypailo, R., Ellis, K.J. 2013. Solid anthropomorphic infant whole body DXA phantom: Design, evaluation, and multisite testing. Pediatric Research. 74(5):486-493.

Interpretive Summary: Dual-energy X-ray absorptiometry (DXA) is a technique used to measure bone, lean, and fat in the body. DXA instruments use special models called phantoms for calibration and quality control. Commercial phantoms are available for spine, hip, and adult whole body scans. There are no commercial phantoms representing infants. We designed and built a phantom that closely matched a 7 kg human infant in body shape and size. We used PVC, nylon mix, and polyethylene to represent bone, lean, and fat, in that order. We scanned the phantom several times to test DXA precision. We also scanned the phantom a number of times for about a month. The short- and long-term results were not significantly different. We then shipped the phantom to six other sites for scanning. Bone results were significantly different from each other in most cases. Three of the instruments differed in fat and lean results. The two Hologic models (Delphi and Discovery) gave different results for all three measures. The phantom design imitated bone, lean, and fat fairly well, and showed good reproducibility. Results from several DXA instruments were inconsistent. This showed us that we cannot directly compare scans from different machines. Instrument cross-calibration would be required in any multi-center studies.

Technical Abstract: Dual energy X-ray absorptiometry (DXA) requires phantoms for quality control and cross-calibration. No commercially available phantoms are designed specifically for infant whole-body scanning. We fabricated a phantom closely matching a 7-kg human infant in body habitus using PVC, nylon-mix, and polyethylene for bone, lean, and fat, respectively, to evaluate comparability of instruments used in infant body composition studies. We scanned the phantom multiple times for short- and long-term repeatability, then shipped it to six other sites for comparison scans. All instruments were Hologic Delphi or Discovery models. Scan analyses were done in-house (Hologic V12.1). Short- and long-term results were not significantly different. Nylon-mix underrepresented expected lean values by 5%, PVC underrepresented bone by 12%, and polyethylene overrepresented fat by 30%. Precision values were: lean approximately 3%; bone approximately 3.5%; fat = 5.5% to 7.5%. Instruments differed significantly for bone mineral and density results in most instances. Three instruments differed in fat and lean. The two Hologic models differed significantly in all compartments except bone density. The phantom design came close to emulating bone, lean, and fat, and showed good reproducibility. Significant differences among various DXA instruments highlight the necessity of cross-calibration for any multi-center studies.