DEXA Scan Used to Detect Osteoporosis
DEXA scan is an instrument used to measure the density of bones. DEXA stands for dual energy X-ray absorptiometry. It is now also called DXA scan. Measurements of bone mineral density are important in many areas of science, but its most important use is found in clinical assessment of osteoporosis (which is a disease in which there is decreased bone mineral density, possibly due to menopause, malnutrition and various other factors).
Working of the DEXA Scan
In a DEXA scan, the patient is placed between two sources of X-ray radiation and a detector. The two sources of X-ray radiation emit X-rays of different energy levels. These X-rays penetrate the body depending on the density of the body tissues i.e. denser tissues do not allow X-rays to pass through. The X-rays transmitted out on the other side are detected by an electronic detector, which then calculates the density of the entire tissue region between the X-ray source and the detector.
It also calculates the density of specific tissue such as bone by subtracting the other soft tissue absorption value from the source, and hence can gives a clear idea of the bone mineral density. Using two X-ray sources is simply to get a more accurate reading, by sending one beam through soft tissue area only, and the other through the bone.
DEXA scan can also be used to calculate total body fat content. The scan is similar to any normal X-ray scanning procedure and takes anywhere between 10 to 15 minutes.
When is it recommended?
DEXA scans are recommended for people who are at a higher risk of osteoporosis. Osteoporosis reduces bone mineral density (BMD), and this leads to increased fragility of the bones and fractures. It is thus important to measure the bone mineral density for patients of osteoporosis, and this can be done by the use of DEXA scan. People with high risk of osteoporosis are women with an early menopause or women who is in post menopause but not taking estrogen, those taking any kind of steroid medication, having a maternal history of hip fractures, are a post-menopausal woman who is tall or thin (having a low body mass index i.e. a body mass index less than 19 or underweight), women having amenorrhea, men and women having disorders associated with osteoporosis (such as coeliac disease) or even thyroid disorders. These groups of people should generally have a DEXA scan done on a regular basis.
Benefits of DEXA Scan
The DEXA scan provides a wide range of benefits. It is simple, non-invasive and quick to perform on patients, without the requirement of anesthesia of any sort. The test is considered to be the most accurate available method to determine bone mineral density, and thus diagnose osteoporosis. Although the only drawback is that use of X-rays can be harmful and cause cancer. However, the dose of the radiation is generally too low to show any side effects, and the incidence of cancer is also negligible. Nevertheless, DEXA scan is still not allowed to be performed on pregnant women, as the X-ray radiation can be harmful to the fetus.
Limitations of a DEXA Scan
Although a DEXA scan can inform the physician whether the patient is prone to fractures or is osteoporotic, it can in no way predict who will have a fracture. Even though it is an accurate means of measuring bone density, DEXA scans are not used for measuring bone density in cases of vertebral compression fractures (spinal deformities). A DEXA scan done on the extremities such as the hands, would give a relative idea of the bone mass in other parts of the body, however, it is known that bone mineral density varies from place to place within the same body. Hence scanning of the peripheral parts will in no way indicate the actual bone mineral density of the spine.
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