Bone density scanning, also called dual-energy x-ray absorptiometry or bone densitometry (BMD), is a special form of X-ray technology that is used to determine bone strength and measure bone loss.
The BMD machine employs low-dose X-rays with two distinct energy peaks through the bones being examined. One peak is absorbed mainly by soft tissue and the other by bone. The soft tissue amount is subtracted from the total and what remains is the bone mineral density.
A BMD scan is usually performed on the lower spine and hips. A special computer is used to measure the density of the bone in these spots and from there determine if osteoporosis is present.
This examination is usually done on an outpatient basis. To measure bone density in the hip and spine, you will be asked to lie on a padded table and the legs may be supported on a padded box to flatten the pelvis and lower (lumbar) spine. To assess the hip, the foot is placed in a brace that rotates the hip inward. In both cases, the detector is slowly passed over the area, generating images on a computer monitor.
You should hold very still and may be asked to keep from breathing for a few seconds while the X-ray picture is taken to reduce the possibility of a blurred image.
The BMD bone density test is usually completed within 15 minutes, depending on the equipment used and the parts of the body being examined.