Photon absorptiometry: Difference between revisions

From Citizendium
Jump to navigation Jump to search
imported>Meg Taylor
(subpages)
imported>Howard C. Berkowitz
 
(5 intermediate revisions by the same user not shown)
Line 1: Line 1:
{{subpages}}
{{subpages}}
In [[medicine]], '''photon absorptiometry''', also called '''x-ray densitometry''', '''dual-energy x-ray absorptiometry''' ('''DEXA Scan''' or '''DXA Scan'''), '''dual photon absorptiometry''' ('''DPX Scan'''), 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 gadolinium 153, iodine 125, or americum 241 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>
{{TOC|right}}
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>
{| class="wikitable"
|-
! 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==
==Measurement of bone density==
{{main|Bone density}}
{{main|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.  
[[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.  
 
==Fluid and soft tissue measurement==
===T-score===
"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 <sub>125</sub>I and <sub>241</sub>Am 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. " <ref>{{citation
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>:
| title = Photon absorptiometry of soft tissue and fluid content: the method and its precision and accuracy
* [[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.
| author = R M Witt and R B Mazess
* [[Osteopenia]] is defined as less than -1.0 and greater than -2.5
|journal = Physics in Medicine and Biology
* Normal is a T-score of -1.0 or higher
| volume 23 | issue = 4
 
|page = 620
===Z-score===
|doi= 10.1088/0031-9155/23/4/005}}</ref>
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>


==Fat and muscle==
It has been used experimentally to measure abdominal fat,  <ref>{{citation
| journal = Int J Obes.
| date = 1990 July
| volume = 14 | issue = 7 | pages = 603-11.
| title = Direct measurement of abdominal fat by dual photon absorptiometry.
| author - Schlemmer A, Hassager C, Haarbo J, Christiansen C.
| url = http://www.ncbi.nlm.nih.gov/pubmed/2228395}}</ref> as well as total body fat and lean body mass.


==References==
==References==
<references/>
{{reflist|2}}

Latest revision as of 20:59, 25 May 2010

This article is a stub and thus not approved.
 Main Article
 Discussion
Related Articles  [?]
Bibliography  [?]
External Links  [?]
Citable Version  [?]
 
https://en.citizendium.org/wiki/index.php?title=Photon_absorptiometry&printable=yes
This editable Main Article is under development and subject to a disclaimer.

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.

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]

Fat and muscle

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

References

  1. ↑ Anonymous (2024), Photon absorptiometry (English). Medical Subject Headings. U.S. National Library of Medicine.
  2. ↑ R M Witt and R B Mazess, "Photon absorptiometry of soft tissue and fluid content: the method and its precision and accuracy", Physics in Medicine and Biology (no. 4): 620, DOI:10.1088/0031-9155/23/4/005
  3. ↑ "Direct measurement of abdominal fat by dual photon absorptiometry.", Int J Obes. 14 (7): 603-11., 1990 July
Retrieved from "https://citizendium.org/wiki/index.php?title=Photon_absorptiometry&oldid=618311"