Dual Energy X-ray Absorptiometry (DEXA Scan)
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Top Contributors - Carin Hunter, Lucinda hampton, Tarina van der Stockt and Kim Jackson
Objective[edit | edit source]
Dual Energy X-ray Absorptiometry[1] (or DEXA, or bone densitometry) is used primarily for osteoporosis [2]tests. It is not projection radiography, as the X-rays are emitted in 2 narrow beams that are scanned across the patient, 90 degrees from each other. Usually the hip (head of the femur), lower back (lumbar spine) or heel (calcaneum) are imaged, and the bone density (amount of calcium) is determined and given a number (a T-score). It is not used for bone imaging, as the image quality is not good enough to make an accurate diagnostic image for fractures, inflammation etc. It can also be used to measure total body fat, though this isn't common. The radiation dose received from DEXA scans is very low, much lower than projection radiography examinations.
Intended Population[edit | edit source]
The World Health Organization (WHO) established dual x-ray absorptiometry tests scans (DEXA) of the central skeleton is the best test for assessing bone mineral density
Method of Use[edit | edit source]
Bone density test results are reported using T-scores. T-scores are relative to how much higher or lower your bone density is compared to that of a healthy 30 year old adult
- A t-score reflects the difference between the measured bone mineral density and the mean value of bone mineral density in young adults.
- It is measured in standard deviations.
- The WHO has defined normal bone mineral density for women as a t-score within one standard deviation of the young adult mean.
- Scores between negative 1 and negative 2.5 reflect a diagnosis of osteopenia.
- Scores below negative 2.5 reflect a diagnosis of osteoporosis.
DEXA stands for dual energy X-ray absorptiometry. This technique was introduced for commercial use in 1987. It sends two X-ray beams at different peak energy frequencies to the target bones.
One peak is absorbed by soft tissue and the other by bone. When the soft tissue absorption amount is subtracted from the total absorption, the remainder is your bone mineral density.
The test is noninvasive, fast, and more accurate than a regular X-ray. It involves an extremely low level of radiation.
