- Osteoporosis Slideshow Pictures
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- Bone density scan facts
- What is osteoporosis?
- How does osteoporosis occur?
- What is bone mineral density (BMD)?
- Who invented the bone density scan?
- Who performs bone density scans?
- Where is a bone density test done?
- What information is on a DXA report?
- Why is bone mineral density measurement important?
- What is the relationship between BMD and fracture risk?
- Who should have BMD testing?
- How is BMD measured?
- What are other methods of measuring BMD?
- How often should DXA scans be repeated to monitor treatment?
- What is the cost of DXA?
- What about the accuracy of BMD testing in the doctor's office using smaller equipment?
Quick GuideWhat Is Osteoporosis? Treatment, Symptoms, Medication
How is BMD measured?
Dual energy X-ray absorptiometry, or DXA, is the most common method to measure a patient's BMD. DXA, or densitometry, is relatively easy to perform and the amount of radiation exposure is low. A DXA scanner is a machine that produces two X-ray beams, each with different energy levels. One beam is high energy while the other is low energy. The amount of X-rays that pass through the bone is measured for each beam. This will vary depending on the thickness of the bone. Based on the difference between the two X-ray beams, the bone density can be measured. The radiation exposure from a DXA scan is actually much less than that from a traditional chest X-ray.
At present, DXA scanning gives information on the BMD two main areas, the hip and spine. Another bone that is often evaluated is the bone of the forearm. Although osteoporosis involves the whole body, measurements of BMD at one site can be predictive of fractures at other sites. Scanning generally takes 10 to 20 minutes to complete and is painless. The patient needs to be able to lie still on the table during the testing. There is no IV or other injection needed for this test. In preparation for a DXA, on the day of the test, you may eat a normal meal, but you should not take any calcium supplements for 24 hours prior to the test.
Certain conditions can alter the results of the DXA scan, making result less reliable. These include a lumbar spinal deformity (scoliosis), extensive degenerative arthritis, a large amount of calcium in the blood vessels (atherosclerosis), or multiple fractures. These conditions can falsely elevate the measured BMD with the DXA scan.