A bone scan is a type of test procedure that is done in order to measure the activity of bone cells. It is done by injecting a slightly radioactive material, called a tracer, into a vein in the patient’s arm. Over the course of a few hours, about half of the tracer is picked up by bone cells, while the other half is filtered out of the body by the kidneys. The tracer is attracted to areas of bone that are highly active, and this can be viewed with a special camera that detects the radiation given off by the tracer. A bone scan is often used to diagnose bone problems such as stress fractures, cancerous lesions, or other conditions that cannot be seen clearly in a traditional X-ray.
The activity and function of cells in the bones is what a bone scan is meant to read. Many people think of bones as static, dry structures that provide support to the body, and do little else. In reality, bones are alive and active, metabolizing nutrients and repairing problems like any other tissue in the body. Certain problems can cause changes in bone metabolism. These changes can be observed through a bone scan, and a doctor can use the results to diagnose problems and suggest treatments.
The camera that detects the radiation from the injected tracer sees areas that absorb little or no tracer as dark spots. These are normal in certain places, but an abnormal dark spot may indicate a lack of blood supply to that area, or the presence of certain types of cancer. In areas where the bone is rapidly growing or being repaired, more tracer will be absorbed and the scan will show a light-colored area or “hot spot.” While a hot spot can also be normal, it may indicate problems such as arthritis, an infection, or the presence of a tumor.
The amount of radiation absorbed by the body during a bone scan is usually small enough to be perfectly safe. However, a patient who is or might be pregnant should consult with a physician before receiving an injection of a radioactive tracer. If there is a legitimate medical justification for it, the bone scan will not normally be delayed. In rare cases, a patient may suffer an allergic reaction to the tracer, but a bone scan ordinarily poses no greater risk than a conventional X-ray.