Photon absorptiometry: Difference between revisions

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In [[medicine]], '''photon absorptiometry''' --[[User:Howard C. Berkowitz|Howard C. Berkowitz]] 01:05, 26 May 2010 (UTC)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 <sub>153</sub>[[gadolinium]], <sub>126</sub>[[iodine]] 125, or <sub>241</sub>[[americium]] 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 density|bone mineral content]], especially for the diagnosis of [[osteoporosis]], and also in measuring [[bone density|bone mineralization]]."<ref>{{MeSH}}</ref>
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 <sub>153</sub>[[gadolinium]], <sub>126</sub>[[iodine]] 125, or <sub>241</sub>[[americium]] 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 density|bone mineral content]], especially for the diagnosis of [[osteoporosis]], and also in measuring [[bone density|bone mineralization]]."<ref>{{MeSH}}</ref>
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{{main|Bone densitometry}}
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[[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.  
[[Bone density]] is generally scored by two measures, the [[Bone densitometry#T-score|T-score]] and the [[Bone densitometry#Z-score|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.  
 
===T-score===
The T-score is a comparison of a patient's [[bone density]] to that of a healthy thirty-year-old.  The criteria of the [[World Health Organization]] are<ref name="WHOcriteria">{{cite web | author=WHO Scientific Group on the Prevention and Management of Osteoporosis (2000 : Geneva, Switzerland) |url=http://whqlibdoc.who.int/trs/WHO_TRS_921.pdf |title=Prevention and management of osteoporosis : report of a WHO scientific group| year=2003 |accessdate=2007-05-31 |format=pdf |work=}}</ref>:
* [[Osteoporosis]] is defined as -2.5 or lower, meaning a bone density that is two and a half standard deviations below the mean of a thirty year old woman.
* [[Osteopenia]] is defined as less than -1.0 and greater than -2.5
* Normal is a T-score of -1.0 or higher
 
===Z-score===
The Z-score is a comparison of a patient's [[bone density]] to the average [[bone density]] of their, sex, and race. This value is used in premenopausal women, men under aged 50, and in children.<ref name="pmid16014886">{{cite journal |author=Raisz LG |title=Clinical practice. Screening for osteoporosis |journal=N. Engl. J. Med. |volume=353 |issue=2 |pages=164–71 |year=2005 |month=July |pmid=16014886 |doi=10.1056/NEJMcp042092 |url=http://content.nejm.org/cgi/pmidlookup?view=short&pmid=16014886&promo=ONFLNS19 |issn=}}</ref>
 


==References==
==References==
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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


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.

References

  1. ↑ Anonymous (2024), Photon absorptiometry (English). Medical Subject Headings. U.S. National Library of Medicine.
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