Dual Energy Xray Absorptiometry

Dual-energy X-ray absorptiometry (DEXA) is a method originally used to determine bone mineral density. For a few years now, it has also been used to study body composition, and to quantify fat and fat-free mass in particular.

DEXA explores the body regions of interest by X-ray emissions at two different energy levels [38]. The different photon attenuation at the two levels depends on the different tissue composition, enabling the bone mineral content and soft tissues to be extrapolated. The different relationship between low- and high-energy photon attenuation enables fat and fat-free mass in the soft tissues to be distinguished.

DEXA yields a high resolution and accuracy with a short acquisition time and consequently with minimal exposure (1.5 mR). The method had a good reproducibility (coefficient of variation) for total body fat mass (2-3%), total body fat-free mass, total body lean soft tissue (1-2%), arm lean soft tissue (3-4%), and leg lean soft tissue (1-2%) [39-41]. Moreover, it is sensitive in assessing minimal changes in body composition [42]. The method has been validated against multislice computed tomography scans, magnetic resonance imaging and a four-compartment model in young and older people [40,43,44].

Measurement of body compartments using DEXA is theoretically independent of FFM hydration status, but variations in the relationship between TBW and FFM may interfere with the accuracy of the method. Recent studies have reported, however, on the validity of DEXA in detecting variations in FFM due to hydration disorders.

The method requires little effort on the part of the subject, thus allowing for frail subjects to be also evaluated.

Unlike many other body composition methods, moreover, DEXA has the potential for assessing the composition of the whole body as well as body regions [45]. At the present time, for example, appendicular skeletal muscle mass (ASMM) evaluation, measured as the sum of the fat-free soft tissue masses of arms and legs, as detected by DEXA, is considered the gold standard for the diagnosis of sarcopenia [46,47]. Subjects are considered sar-copenic when they have ASMMI (ASMM divided by height squared) values 2 standard deviations below the mean ASMMI values (7.26 for males and 5.45 for females) for a young adult referral population from the Rosetta study [47].

Pregnancy Guide

Pregnancy Guide

A Beginner's Guide to Healthy Pregnancy. If you suspect, or know, that you are pregnant, we ho pe you have already visited your doctor. Presuming that you have confirmed your suspicions and that this is your first child, or that you wish to take better care of yourself d uring pregnancy than you did during your other pregnancies; you have come to the right place.

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