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Bone scan

Bone imaging is a study to visually detect bone abnormalities. Such imaging studies include magnetic resonance imaging (MRI), X-ray computed tomography (CT) and especially nuclear medicine. In the latter case the patient is injected with a small amount of radioactive material such as 600 MBq of technetium-99m-MDP and then scanned with a gamma camera, a device sensitive to the radiation emitted by the injected material. In order to view small lesions (less than 1 cm) especially in the spine, single photon emission computed tomography (SPECT) imaging techique may be required. In the United States, most insurance companies require separate authorization for SPECT imaging.

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About half of the radioactive material is localized by the bones. The more active the bone turnover, the more radioactive material will be seen. Some tumors, fractures and infections show up as areas of increased uptake. Others can cause decreased uptake of radioactive material. Not all tumors are easily seen on the bone scan. Some lesions, especially lytic (destructive) ones, require positron emission tomography (PET) for visualization.

About half of the radioactive material leaves the body through the kidneys and bladder in urine. Anyone having a study should empty their bladder immediately before images are taken.

In evaluating for tumors, the patient is injected with the radioisotope and returns in 2-3 hours for imaging. Image acquisition takes from 30 to 70 minutes, depending if SPECT images are required. If the physician wants to evaluate for osteomyelitis (bone infection) or fractures, then a Three Phase Bone Scan is performed where 20-30 minutes of images (1st and 2nd Phases) are taken during the initial injection. The patient then returns in 2-3 hours for additional images (3rd Phase). Sometimes late images are taken at 24 hours after injection.

Pregnant patients should consult with a physician before consenting to radioactive injections. The total amount of radiation is small, so the bone scan should not be delayed if there is a true medical necessity.