bone scan
Meaning of bone scan: An imaging test that maps repair activity across the whole skeleton in one pass, often long before an x-ray shows anything.
Definition of bone scan
A bone scan is a nuclear medicine test that shows where bone is being actively built or repaired. A small amount of a radioactive tracer is injected into a vein, and it settles wherever bone turnover is high. A camera then records the tracer across the whole skeleton over several minutes, and areas of busy repair appear as bright spots.
How does the tracer find the bone?
The tracer is a phosphate-like compound tagged with technetium, a metal that gives off a weak signal a gamma camera can detect. It binds to the mineral surface of bone, and it binds most where new mineral is being laid down. Imaging is delayed by a few hours after the injection so that tracer not taken up by bone has cleared into the urine, which is what gives the pictures their contrast. The radiation dose is comparable to that of a computed tomography study, and the tracer decays within hours.
What does a bright spot mean?
Only that bone is repairing itself there. It does not say why. A healing rib fracture, an arthritic joint, an infection, Paget disease and a deposit of cancer can all produce the same appearance. The pattern is what carries the information. Symmetrical uptake at large joints usually reflects wear. Multiple scattered spots along the spine, ribs and pelvis in someone with a known tumor suggest spread. A single hot area in a long bone in an athlete suggests a stress fracture. Findings are read alongside plain films, CT or MRI, and sometimes a biopsy.
How is it different from other bone imaging?
| Test | What it measures | What it uses |
|---|---|---|
| Bone scan | Bone turnover across the whole skeleton | An injected radioactive tracer |
| Bone mineral density scan | How much mineral the bone contains | A very low dose of x-rays |
| PET scan | Metabolic activity in tumor and other tissue | A different injected tracer, often a labeled sugar |
| Plain x-ray | Structure and shape | A single burst of x-rays |
Why is it still used?
It covers the entire skeleton in one study and at modest cost, and it registers change earlier than a plain film, which shows nothing until a substantial fraction of the bone mineral at a site has been lost. That makes it useful when the question is where to look rather than what a known lesion is: staging cancers that favor bone, investigating unexplained bone pain, and confirming bone cancer or a suspected stress injury when x-rays are normal.
Also known as
Used in a sentence
A bone scan was requested to look for skeletal spread before treatment was planned.
Good to know
A hot spot records bone turnover rather than a diagnosis, and healing fractures, arthritis and infection light up in the same way tumor deposits do, so the pattern is interpreted alongside other imaging.