Scintigraphy is the name for the process used to scan bone. Radioactive tracers injected into the body emit radiation waves that a gamma camera can detect. The tracers attach to molecules that are drawn into and accumulate in the bone. The gamma camera delivers information into a computer that creates an image of the scanned area.
A normal reaction to the radioactive tracer shows up as a grey area on the image. The grey is a continual, consistent colour and indicates an area that is not ravaged by arthritis or any other disease or fracture.
"Hot spots" are darker than grey spots, indicating lots of tracer activity. These dark spots show an increase in bone metabolism. Hot spots can be caused by fractures, arthritis, bone cancer or infection.
"Cold spots" are much lighter--even white in some cases--than the normal grey spots. They indicate a decrease in bone metabolism which can be caused by a cancer called multiple myeloma or by a lack of blood supplied to the bone.
Tracers indicate arthritis when they gather on the surface of a joint. The arthritis appears dark along the joint. Knees, hips, the spine, hands and feet are usually where arthritis is found.
A bone scan will help diagnose arthritis in the early stages of the disease. X-rays do not usually assist with early diagnosis but can verify arthritis as it develops. Arthroscopy, the insertion of a small camera into the joint area, supplies a direct look at the joint and delivers a clearer view of the arthritis.