ABSTRACT:A study was conducted to validate the use of a quantitative magnetic resonance (QMR) device for measuring the body composition of infants and neonates weighing Ͻ12 kg using the pig as a model. A total of 25 piglets weighing between 2 and 12 kg were studied. Body composition was assessed by QMR, dual-energy x-ray absorptiometry (DXA), and whole-body chemical analysis (CA) of carcass for lipid and water content. The precision, mean and SD of repeated measurements, of QMR to estimate fat mass (FM), lean mass (LM), and total body water (TBW) for five consecutive scans with reposition was 12.5, 32.0, and 36.0 g, respectively. QMR measures of FM, LM, and TBW were highly and significantly correlated with CA of carcass. In terms of accuracy, mean difference between QMR and CA (percent of mean value for CA), QMR overestimated FM by 40 g (4.7%), overestimated LM by 114.9 g (2.1%), and underestimated TBW by 134.6 g (3.1%). This study concludes that QMR provides precise and accurate measures of FM, LM, and TBW in piglet weighing up to 12 kg. These results suggest that QMR can provide valuable body composition data in longitudinal studies in infants. A ccurate assessment and tracking of infant body composition is useful in evaluating the amount and quality of weight gain, which can provide key information in both clinical and research settings. Body composition analysis (BCA) can be used to monitor and evaluate infant growth patterns, efficacy of nutritional and medical interventions, progression of chronic disease, and recovery from malnutrition (1-5).A large variety of nondestructive BCA methods have been developed, each with its advantages and shortcomings, such as air-displacement plethysmography (ADP) (6), bioelectrical impedance analysis (BIA) (7), dual-energy x-ray absorptiometry (DXA) (8), total-body electrical conductivity (TOBEC) (9), total body potassium (TBK) (10), isotope dilution (11), skin-fold thickness measurements (SFT) (12), multicompartment models (13), computed tomography (CT) (14), MRI (15), magnetic resonance spectroscopy (MRS) (16), and quantitative magnetic resonance (QMR) (17).Common shortcomings include complexity and time needed to obtain results (multicomponent models, TBK, isotope dilution, MRI, and MRS), immobilization requirement (MRI, MRS, CT, and DXA), expensive equipment (MRI, MRS, CT, DXA, QMR, and TOBEC), reliability and correspondence of relations between measured quantities and body components (BIA, TOBEC, ADP, and SFT), radiation exposure (CT and DXA), and potential vulnerability to oversimplification (ADP and SFT).QMR devices stand out in that they are fast and very easy to use, require no sedation or anesthesia, and are free of radiation, while capable of unsurpassed precision and high accuracy. Typical scan times range from Ͻ1 min to Ͻ4 min in different specific devices and applications, and less than half an hour of training is sufficient for a typical user.The QMR method is a branch of nuclear magnetic resonance (NMR), for whole body measurement of fat, lean tissues, free...