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Body Composition: Dual Energy X-Ray Absorptiometry

Body composition can be measured through techniques like dual energy X-ray absorptiometry (DEXA) scans, which provide accurate measurements of bone mineral content, bone mineral density, lean tissue mass, and fat tissue mass. DEXA scans are highly reproducible and expose subjects to less radiation than a flight. However, some errors still exist in the DEXA method. Air displacement plethysmography is an alternative that measures body volume through air displacement to estimate body density and composition. Bioelectrical impedance analysis uses electrical resistance to estimate body fat but is sensitive to hydration status. The body volume indicator uses 3D scanning techniques like smartphone photos to calculate body volume and fat distribution by comparing to MRI data.

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52 views1 page

Body Composition: Dual Energy X-Ray Absorptiometry

Body composition can be measured through techniques like dual energy X-ray absorptiometry (DEXA) scans, which provide accurate measurements of bone mineral content, bone mineral density, lean tissue mass, and fat tissue mass. DEXA scans are highly reproducible and expose subjects to less radiation than a flight. However, some errors still exist in the DEXA method. Air displacement plethysmography is an alternative that measures body volume through air displacement to estimate body density and composition. Bioelectrical impedance analysis uses electrical resistance to estimate body fat but is sensitive to hydration status. The body volume indicator uses 3D scanning techniques like smartphone photos to calculate body volume and fat distribution by comparing to MRI data.

Uploaded by

alkazum
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© © All Rights Reserved
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Body composition

Body composition measurement with dual energy X-ray absorptiometry (DEXA) is used increasingly


for a variety of clinical and research applications. A DEXA scan requires medical supervision by a
radiologist and some consider it to be the new "Gold Standard" in body composition testing. Total
body scans using DEXA give accurate and precise measurements of body composition, including
bone mineral content (BMC), bone mineral density (BMD), lean tissue mass, fat tissue mass, and
fractional contribution of fat.[6]
The estimation of body fatness from body density (by means of underwater weighing) was accepted
as the "gold standard" for many decades. Some researchers now claim that whole body scanning
techniques (e.g. "DEXA") are the new "gold standard". But these claims are somewhat dubious since
the scanning algorithms are validated against body composition assessments based on fractional
density from underwater weighing.
DEXA measurements are highly reproducible if the same type of machine is used (citation needed),
making them excellent for monitoring pharmaceutical therapy, nutritional or exercise intervention,
sports training and or other body composition altering programs. They are also fast, simple, non-
invasive, and expose the subject to a level of x-rays less than that of a cross-country flight. DEXA
exams provide both total body and up to 14 regional (trunk, individual arms & legs, android, gynoid,
etc.) results. However, the role of DEXA in clinical evaluations and research studies has been
questioned by Wang et al.[7] who stated that "the errors of the DXA [DEXA] method are still of
concern if it were to be used as the criterion."
Another technique for measuring body composition has been developed for measuring body volume
using a different method than underwater weighing. The technique uses air as opposed to water and
is known as air displacement plethysmography (ADP). Subjects enter a sealed chamber that
measures their body volume through the displacement of air in the chamber. Body volume is
combined with body weight (mass) in order to determine body density. The technique then estimates
the percentage of body fat and lean body mass (LBM) through empirically derived equations similar
to those used with underwater weighing (for the density of fat and fat free mass).

From conductivity[edit]
Another method is bioelectrical impedance analysis (BIA), which uses the resistance of electrical
flow through the body to estimate body fat. Unfortunately, BIA is highly sensitive to hydration status
and water intake. Drinking water dilutes the electrolytes in the body making it less conductive as
does increasing body fat. Recent advancements such as 8-point electrodes, multi-frequency
measurements, and Direct Segmental Analysis [8], have improved the accuracy of BIA machines [9].
BIA machines have found acceptance in medical, fitness and wellness space owing to their ease-of-
use, portability, quick measurements and cost efficiency.

Body Volume Indicator[edit]


The Body Volume Indicator (BVI) is a technique used for measuring body shape. Initially, BVI
technology employed white light scanning machines to measure an individuals body shape.
[10]
 However, recent technological advances in 3D measurement have enabled BVI to be calculated
using images taken on a smartphone. Two images are required to create an individual 3D silhouette.
By comparing this 3D silhouette with MRI data, body volume and fat distribution can be
calculated (BVI website).

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