Photon absorptiometry

In medicine, photon absorptiometry is a "noninvasive method for assessing body composition. It is based on the differential absorption of x-rays (or gamma rays) by different tissues such as bone, fat and other soft tissues. The source of (x-ray or gamma ray) photon beam is generated either from radioisotopes such as ₁₅₃gadolinium, ₁₂₆iodine 125, or ₂₄₁americium which emit gamma rays in the appropriate range; or from an x-ray tube which produces x-rays in the desired range. It is primarily used for quantitating bone mineral content, especially for the diagnosis of osteoporosis, and also in measuring bone mineralization."^[1]

Method	Source	Detection levels
Single-photon absorptiometry (SPA)	Isotope	Single
Dual-photon absorptiometry (DPA)	Isotope	Dual
Dual-Energy X-Ray Absorptiometry (DEXA)	X-ray	Dual

[edit] Measurement of bone density

For more information, see: Bone densitometry.

Bone density is generally scored by two measures, the T-score and the Z-score. Scores indicate the amount one's bone mineral density varies from the mean. Negative scores indicate lower bone density, and positive scores indicate higher.

[edit] Fluid and soft tissue measurement

"Dichromatic absorptiometry allows the measurement of soft tissue and fluid content, and their changes. The technique uses linear transmission scans made across the limbs with a congruent ₁₂₅I and ₂₄₁Am dual-photon source and a sodium iodide-thallium crystal with photomultiplier tube detector."Patient measurements could be made at the bedside with the mobile system. Factors affecting the precision and accuracy were evaluated theoretically and experimentally. " ^[2]

[edit] Fat and muscle

It has been used experimentally to measure abdominal fat, ^[3] as well as total body fat and lean body mass.

[edit] References

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