QMR: validation of an infant and children body composition instrument using piglets against chemical analysis.

OBJECTIVE: This study was undertaken to validate the first quantitative nuclear magnetic resonance (QMR) instrument designed and built to assess body composition in children from birth to adulthood (up to 50 kg).
DESIGN: A total of 50 pigs weighing between 3.0 and 49.1 kg were studied. Each piglet's body composition was assessed by quantitative nuclear magnetic resonance (QMR, EchoMRI-AH small), whole-body chemical carcass analysis for lipid and water content, and dual-energy X-ray absorptiometry (DXA, Hologic QDR 4500, using infant or adult whole-body scan acquisition programs where appropriate). Twenty-five piglets (3.1-47.2 kg) were randomly selected to calibrate the QMR instrument. The remaining 25 piglets (3.0-49.1 kg) were used to validate the instrument.
RESULTS: The precision of QMR to estimate fat mass (FM), fat-free mass (FFM) and total body water (TBW) for five consecutive scans was excellent (1.3, 0.9 and 0.9%, respectively). QMR measures of FM were highly and significantly correlated with chemical carcass analyses and DXA measures (r(2)=0.99 and r(2)=0.98, respectively). QMR and DXA FFM results were highly correlated (R(2)=0.99, P<0.01). TBW measures were strongly correlated between QMR and carcass analyses (R(2)=0.99, P<0.01). QMR overestimated FM by 2% and DXA measures (using the infant and adult scan programs) overestimated FM by 15% on average.
CONCLUSION: QMR provides precise and accurate measures of FM, FFM and TBW in piglets weighing up to 50 kg. As the piglet is considered to be an excellent model of human development, these data suggest that QMR should provide the opportunity to acquire valuable body composition data in longitudinal studies in children, which is not possible or practical with other commercially available instrumentation.