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This is a test to look for any areas of bone where there is a lot of activity.
The activity could be bone breaking down, or bone repairing itself. There are several possible reasons for bone activity - cancer is one of them, but other reasons include arthritis, fractures and bone infections, so the test results need to be carefully interpreted.
For the test, a mildly radioactive substance called a 'tracer' is injected into a vein in the arm. This small amount of radioactive material will not do you any harm.
You will be asked to wait for around three hours, whilst the tracer substance is taken up by the bone. The doctor will ask you to drink plenty of fluids while you are waiting, as this will help flush the injected substance through your body.
You will also need to pass urine just before you return to help get rid of any substance in your bladder, to make sure this doesn't interfere with the scan.
When you are ready, you will be asked to lie down on an X-ray couch ready for the scan. You need to keep as still as possible during the scan. The gamma camera will then take pictures of the whole of your skeleton. The tracer helps to show up any active areas of bone – these are called hot spots. The scan takes about an hour.
Having 'hot spots' doesn't necessarily mean that there is cancer in your bones. Bone can break down and repair for other reasons. If you have arthritis, for example, this will also show up on the scan.
After the scan, you will be able to go home. It will take up to 24 hours for the tracer substance to get out of your system. It will help if you drink plenty of fluids during this time.