equipment required: DEXA machine, which differentiates
body weight into the components of lean soft tissue, fat soft
tissue and bone, based on the differential attenuation by tissues
of two levels of x-rays.
procedure: The person lays on the whole body scanner, with the x-ray sources mounted beneath a table and a detector overhead. The person is scanned with photons that are generated by two low-dose x-rays at different energy levels. The body's absorption of the photons at the two levels is measured. The ratios can be then used to predict total body fat, fat-free mass, and total body bone mineral. The procedure can take about 10 - 20 minutes.
advantages: This method is precise, accurate, and reliable.
DEXA measurements are based on a three compartmental
model (total body mineral (from bones), fat-free soft (lean) mass, and fat tissue mass) rather than two compartment as in most other methods. DEXA
can also distinguish regional as well as whole body parameters
of body composition. As such, it is considered a reference standard, and the latest body composition research uses this method.
disadvantages: The equipment is expensive, and often
requires trained radiology personnel to operate.
other comments: If not for the limiting price of measurement,
DEXA would be considered the criterion method of body composition