Calibration and validation of EchoMRI™ whole body composition analysis based on chemical analysis of piglets, in comparison with the same for DXA.

A study was conducted to appraise a new EchoMRI™ device for body composition analysis (BCA) of infants and to compare it with dual energy X-ray absorptiometry (DXA), using chemical analysis as a reference method.The calibration part of the study included cross-validation comparisons between EchoMRI™ measurements of awake, anesthetized and dead piglets of the calibration set. It also included comparison of two different approaches to refining the calibration of EchoMRI™, by low- or by high-dimensional linear regressions. Only the low-dimensional approach was applied to DXA.The validation part yielded EchoMRI™ accuracy of 27 g and 70 g for fat and total water, respectively, on piglets scanned while anesthetized, as compared with 24 g and 57 g, respectively, for DXA.EchoMRI™ precision was found to be 4 g and 7 g for fat and total water, respectively, for anesthetized piglets, as compared to 16 g and 14 g, respectively, for DXA. The differences between fat measurements of awake, anesthetized and dead piglets can be statistically significant, but are comparable in magnitude to random errors.To summarize: Characterization of random errors by CV, especially that of fat, is not suitable for BCA, whereas absolute errors or errors relative to total body weight can be applicable. Low- and high-dimensional regressions offer nearly the same accuracy improvements. Improved DXA and EchoMRI™ offer nearly the same accuracy, within 1% of weight in fat, while EchoMRI™ has better precision, within 0.2 % of weight in fat for anesthetized and dead piglets as compared to DXA's 0.5-0.6%.

Evaluation of a quantitative magnetic resonance method for mouse whole body composition analysis.

OBJECTIVE: To evaluate applicability, precision, and accuracy of a new quantitative magnetic resonance (QMR) analysis for whole body composition of conscious live mice. RESEARCH METHODS AND PROCEDURES: Repeated measures of body composition were made by QMR, DXA, and classic chemical analysis of carcass using live and dead mice with different body compositions. Caloric lean and dense diets were used to produce changes in body composition. In addition, different strains of mice representing widely diverse populations were analyzed. RESULTS: Precision was found to be better for QMR than for DXA. The coefficient of variation for fat ranged from 0.34% to 0.71% compared with 3.06% to 12.60% for DXA. Changes in body composition in response to dietary manipulation were easily detected using QMR. An increase in fat mass of 0.6 gram after 1 week (p < 0.01) was demonstrated in the absence of hyperphagia or a change in mean body weight. DISCUSSION: QMR and DXA detected similar fat content, but the improved precision afforded by QMR compared with DXA and chemical analysis allowed detection of a significant difference in body fat after 7 days of consuming a diet rich in fat even though average body weight did not significantly change. QMR provides a very precise, accurate, fast, and easy-to-use method for determining fat and lean tissue of mice without the need for anesthesia. Its ability to detect differences with great precision should be of value when characterizing phenotype and studying regulation of body composition brought about by pharmacological and dietary interventions in energy homeostasis.

Quantitative magnetic resonance (QMR) method for bone and whole-body-composition analysis.

OBJECTIVE: to evaluate the applicability, precision, and accuracy of the new EchoMRI quantitative magnetic resonance (QMR) method for in-vitro bovine bone analysis and in-vivo whole-body-composition analysis of conscious live mice. RESEARCH METHODS AND PROCEDURES: bovine tibia bone samples were measured by QMR and dual-energy X-ray adsorptiometry (DEXA). Repeated measures of whole-body composition were made using live and dead mice with different levels of fat by QMR and DEXA and by classic chemical analysis of the mouse carcass. RESULTS: bone-mineral density (BMD) and bone-mineral content (BMC) measured in bovine tibia by QMR and DEXA were highly correlated. Precision of fat and lean measurement in mice was found to be better for QMR than for DEXA. The coefficient of variation ( CV) for fat was 0.34-0.71% for QMR compared with 3.06-12.60% for DEXA. DISCUSSION: QMR offers more specific parameters of bone structure than does DEXA. QMR and DEXA did not differ in the total amount of fat detected in live mice but QMR had improved precision. QMR was superior to DEXA in measuring fat in very small mice. CONCLUSIONS: in bone tissue there is a strong correlation between hydrogen NMR signal and bone-mineral density as measured by X-ray. QMR provides a very precise, accurate, fast, and easy to use method for determining fat and lean mass of mice without the need for anesthesia. Its ability to detect differences and monitor changes in body composition in mice with great precision should be of great value in characterizing phenotypes and studying drugs affecting obesity.