Bone scintigraphy
Diagnostics
A nuclear medicine whole-body bone scan. The nuclear medicine whole-body bone scan is generally used in evaluations of various bone-related pathology, such as for bone pain, stress fracture, nonmalignant bone lesions, bone infections, or the spread of cancer to the bone.

A patient undergoing a SPECT bone scan. The patient lies on a table that slides through a scanner, while two gamma cameras rotate around him. Machine operators typically work remotely from another room, shielded from the radiation being emitted by the patient.

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Nuclear medicine bone scans

Nuclear medicine bone scans are one of a number of methods of bone imaging, all of which are used to visually detect boneabnormalities. Such imaging studies include magnetic resonance imaging (MRI), X-ray computed tomography (CT) and in the case of 'bone scans' nuclear medicine. However, a nuclear bone scan is a functional test: it measures an aspect of bone metabolism orbone remodeling, which most other imaging techniques cannot. The nuclear bone scan competes with the FDG-PET scan in seeing abnormal metabolism in bones, but it is considerably less expensive.

Nuclear bone scans are not to be confused with the completely different test often termed a "bone density scan," DEXA or DXA, which is a low-exposure X-ray test measuring bone density to look for osteoporosis and other diseases where bones lose mass, without any bone-rebuilding activity. The nuclear medicine scan technique is sensitive to areas of unusual bone-rebuilding activity because the radiopharmaceutical is taken up by osteoblast cells that build bone. The technique therefore is sensitive to fractures and bone reaction to infections and bone tumors, including tumor metastases to bones, because all these pathologies trigger osteoblast activity. The bone scan is not sensitive to osteoporosis or multiple myeloma in bones; therefore, other techniques must be used to assess bone abnormalities from these diseases.

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Technique

In the nuclear medicine technique, the patient is injected (usually into a vein in the arm or hand, occasionally the foot) with a small amount of radioactive material such as 740 MBq of technetium-99m-MDP and then scanned with a gamma camera, a device sensitive to the radiation emitted by the injected material. Two-dimensional projections of scintigraphy may be enough, but in order to view small lesions (less than 1 cm) especially in the spine, single photon emission computed tomography (SPECT) imaging technique may be required. In the United States, most insurance companies require separate authorization for SPECT imaging.

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/Triphasic 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.

Person undergoing a bone scan on the skull.