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Title: Calibration and Validation of EchoMRI Whole Body Composition Analysis Based on Chemical Analysis of Piglets, in comparison with the same for DXA

Author
item KOVNER, I - Echo Medical Systems
item TAICHER, G - Echo Medical Systems
item Mitchell, Alva

Submitted to: International Journal of Body Composition Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/18/2010
Publication Date: 3/1/2010
Citation: Kovner, I., Taicher, G., Mitchell, A.D. 2010. Calibration and validation of EchoMRI whole body composition analysis based on chemical analysis of piglets, in comparison with the same for DXA. International Journal of Body Composition Research. 8(1):17-29.

Interpretive Summary: A study was conducted to evaluate the accuracy and precision of a new quantitative magnetic resonance (QMR) EchoMRI device body for composition analysis (BCA) of infants and to compare it with dual energy X-ray absorptiometry (DXA). The EchoMRI device measured fat, lean, free water, and total water, and the DXA device measured fat, lean, and bone mineral content. The results of this study indicate that with proper calibration, both DXA and EchoMRI can provide similar good accuracies and precisions in measurements of fat and total body water content of piglets in the 2000 to 4000 g body weight range. As it appears from the validation set of 25 piglets, the precision is 2-4 times better in the case of EchoMRI and the accuracy is 1.1-1.3 times better in the case of DXA. Two additional major advantages of the QMR method over DXA are that QMR does not expose the subject to X-ray radiation and that QMR does not necessarily require immobilization of the subject. These two advantages are most critical for BCA of infants and for longitudinal animal studies.

Technical Abstract: A study was conducted to evaluate the accuracy and precision of a new quantitative magnetic resonance (QMR) EchoMRI device body for composition analysis (BCA) of infants and to compare it with dual energy X-ray absorptiometry (DXA). The EchoMRI device measured fat, lean, free water, and total water, and the DXA device measured fat, lean, and bone mineral content. The evaluation was performed on piglets 1-10 days old, in the 1720-4300 g mass range. The study consisted of two sets of 25 piglets each. The first, calibration set, was used for calibrations of the EchoMRI and DXA devices by chemical analysis as a reference BCA method. Six months later the second, validation set, was used to test the accuracy. Both sets of piglets were used for evaluation of precision. Each piglet was scanned by EchoMRI in three states: awake, anesthetized, and dead; scanned by DXA in two states: anesthetized and dead; and finally subjected to chemical analysis. Each EchoMRI scan was repeated five times and each DXA scan was repeated three times. The calibration part of the study included cross-validation comparisons between EchoMRI measurements of awake, anesthetized and dead piglets of the calibration set weighting in the range of 1720 and 4070 g. 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 of the study was used to evaluate the accuracy of EchoMRI and DXA relative to chemical analysis. The EchoMRI accuracy was found to be about 27 g and 70 g for fat and total water, respectively, on the 25 validation piglets weighting in the range of 2000-4300 g and scanned while anesthetized. The precision of EchoMRI was found to be about 4 g and 7 g for fat and total water, respectively, evaluated for all the 50 piglets scanned anesthetized. The differences between fat measurements of awake, anesthetized and dead piglets evaluated on all the 50 piglets are within the ranges of expected random errors.