A bone mineral density test (BMD) is a safe, painless and reliable test that uses special X-rays to measure how many grams of calcium and other bone minerals are packed into a segment of bone. Dual x-ray absorptiometry (DXA) is the most accurate way to measure BMD. It uses two different X-ray beams to estimate bone density or thickness of your bones. The BMD at the hip and spine has been shown to be the best way of predicting the risk of breaking a bone. The basic idea is that heavier bones will be stronger bones. The information is used to measure the strength of your bones.
Think of light shining through curtains. The denser the fabric the less amount of light will penetrate through the curtains. Similarly, a bone densitometer uses a detector to measure the transmission of small amounts of x-rays (light) through your bones. The amount of light that passes through the bone is measured providing a radiologist with a picture that indicates how dense (thick or thin) your bones are. The denser the bones, the stronger they are and the less likely they are to break. Strong, dense bones allow less of the X-ray beam to pass through them.
When information about bone mineral density is combined with personal and family medical history as well as a physical examination, doctors can get a more complete picture of your bone health!