Photon absorptiometry
In medicine, photon absorptiometry --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 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
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.
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[2]:
- 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.[3]
References
- ↑ Anonymous (2024), Photon absorptiometry (English). Medical Subject Headings. U.S. National Library of Medicine.
- ↑ WHO Scientific Group on the Prevention and Management of Osteoporosis (2000 : Geneva, Switzerland) (2003). Prevention and management of osteoporosis : report of a WHO scientific group (pdf). Retrieved on 2007-05-31.
- ↑ Raisz LG (July 2005). "Clinical practice. Screening for osteoporosis". N. Engl. J. Med. 353 (2): 164–71. DOI:10.1056/NEJMcp042092. PMID 16014886. Research Blogging.