Norland Elite 437A150, Operator'S Manual

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Introduction
When Soft Tissue Composition is resident on the system, soft tissue values are automatically presented for
the computer-generated and operator-defined regions of interest on Whole Body scans and for operator-defined
regions of interest on Research and Small Subject scans. Refer to the appropriate chapters in this manual for
more details on Whole Body and Research and Small Subject scans.
DXA provides independent values of bone mineral content (BMC) and bone mineral density (BMD) and non-
bone lean mass (LEAN), as well as fat mass (FAT) from which the true bone mass fraction is calculated for
Whole Body scans. (This value must be manually calculated for Research and Small Subject scans.) Siri and
Brozek equations for underwater weighing equivalent values are reported in addition to the BMD, BMC, LEAN
MASS and FAT MASS values for Whole Body scans.
Using DXA technology to determine fat content is a much quicker and simpler process than underwater weigh-
ing (UWW), which is often said to be the “gold standard”. Underwater weighing requires that subjects be able
and willing to be completely submerged in water while exhaling rather forcibly. This method is ill suited for sub-
jects who are sick, infirm, unconscious, or afraid of water.
Another advantage of DXA over UWW is its insensitivity to body gas. The effect of gases contained in the body
must be compensated for when using underwater weighing, while the x-ray beam used in DXA is unaffected by
such gases.
Tissue Composition Standards
The soft tissue assessment is based on the following industry standards:
The standard for bone is hydroxyapatite, a substance equal to the mineral component in bone. It is available
in purified form as calcium phosphate tribasic, type IV, from the Sigma Chemical Company of St. Louis, Mis-
souri, USA.
The standard for fat is stearic acid, a fatty acid which closely approximates the triglyceride esters which
make up mammalian fat in molecular composition and in photon attenuation properties.
The standard for lean soft tissue is 0.6% sodium chloride in water. This saline solution closely approximates
the photon attenuation properties of the various lean soft tissues, such as muscle, blood and skin.
Operator's Guide
437D140 Rev. I
6-2 Soft Tissue Composition