A bone scan is a radionuclide imaging test that identifies areas of fracture, infection or new growth in bone.

A number of injuries, painful conditions and diseases may be detected with a bone scan, including most fractures, cancer, arthritis, osteomyelitis (bone infection), shin splints and Paget’s disease, in which bone breakdown occurs more quickly than normal and grows back abnormally.

Bone scans may identify some problems days, months or even years before they might be detected with an x-ray.

Bone scans are performed by injecting small amounts of a radioactive substance called a tracer into the body through a vein in an extremity. The tracer travels throughout the bloodstream and into the bones.  A device called a gamma camera detects radioactivity and is used to produce images of the bones. The procedure is not painful except for the brief discomfort of the injection.

This radioactive substance accumulates in areas of excessive bone activity, called hot spots. Areas where there are less radioactive substances present are called cold spots. The presence of hot or cold spots may indicate problems, such as trauma, infections or cancer. Further tests may be required to correctly identify the cause of abnormal bone activity identified by a bone scan.

A bone scan is a test that produces images of the bone to detect changes in the bone’s metabolism (natural processes that create and use energy).

Bones provide support for the body, store important minerals and contain bone marrow, which manufactures red blood cells. Bones break down and regrow over time as a normal part of body function, a process called bone turnover. Bone turnover can also occur as a result of injury or disease. A bone scan identifies areas of normal and abnormal bone turnover.

A bone scan may be performed on the entire body or just part of it. It is sometimes used instead of an x-ray because it can identify problems an x–ray would not detect. It can also detect some problems earlier than an x–ray.

Bone scans are a type of nuclear medicine (radionuclide imaging), meaning they involve the use of tiny amounts of radioactive materials called tracers (radionuclides). After they are placed in the body, tracers emit waves of radiation. The waves are detected by a device called a gamma camera that picks up radioactivity. Images produced by the camera are analyzed by trained medical professionals.

Depending on what condition the physician is testing for, images may be taken immediately after injection of the radioactive tracer or taken after few hours.

Bone scans differ from x–rays in that x–rays pass radiation through the body to produce pictures on film placed on the other side of the body. A bone scan also differs from a bone mineral density test (DEXA scan), which uses certain low-dose x–rays to test for osteoporosis.

There are numerous injuries, conditions and diseases that a bone scan may identify. These include:

• Fractures. A bone scan may be used to diagnose small or hidden fractures that do not appear on a standard x–ray.
  

  

• Cancer. The test is sometimes used to diagnose cancer in the bone or determine whether a cancer that originated elsewhere in the body, such as the prostate, breast, lung or kidney, has spread (metastasized) to the bone.
  
  
• Degenerative diseases of the bones, such as arthritis. Bone scans can also identify joints that are at potential risk of developing early osteoarthritis after trauma. Occasionally a torn anterior cruciate ligament in the knee may lead to early post-traumatic osteoarthritis that a bone scan may detect earlier than an x-ray.

• Paget’s disease. A disease in which bone breaks down more quickly than normal and, when it grows back, is softer than normal and not as resilient.
  
  
• Osteomyelitis. An acute or chronic bone infection, usually caused by bacteria.
  
  
• Osteomalacia. A condition involving softening of the bones caused by vitamin D deficiency. In children, it is called rickets.
  
  
• Fibrous dysplasia. A disease of the bone in which the bone’s outer layers become thin. The inner bone marrow is replaced by a gritty, fibrous tissue containing sharp, needle–like fragments of bone.
  
  
• Avascular necrosis (osteonecrosis). Disease resulting from the temporary or permanent loss of blood to the bones.
  
  
• Shin splints. This common athletic injury can often be diagnosed during a physical examination. Sometimes a bone scan or other imaging tests are ordered to distinguish shin splints from a stress fracture in the tibia (shinbone). In shin splints the tracer does not accumulate in a localized area, but typically accumulates along the length of the tibia. In stress fractures, the substance accumulates around the area of the fracture.
  
  
• Unexplained pain. A scan may be performed to help identify the cause or location of unexplained bone pain, such as lower back pain.

Bone scans are sometimes used in cases of suspected child abuse because the test can detect patterns of repeated trauma.

Before the test, patients may be required to remove their clothing and wear an examination gown. All jewelry and other metallic objects must be removed so they do not interfere with the test. Pregnant women should inform physicians of their condition prior to the test because it may be harmful due to radiation exposure to the unborn child.

Patients may wish to limit fluid intake or urinate prior to the bone scan because they will be required to drink fluids during the test. Patients may be required to sign a consent form before the test can be performed.

A bone scan is usually performed by a nuclear medicine technologist in the radiology department of a hospital or an outpatient x-ray center. The patient usually sits or lies down while a radioactive substance (called a radiotracer or bone–seeking radionuclide) is injected through a vein in the arm. The amount injected is small and is not harmful to the patient.

For most bone scans, a patient must wait between three and four hours after the injection to allow the radionuclides to circulate through the body. During this time, the individual drinks several glasses of water to urinate frequently, which removes unabsorbed radioactive material from the body. The patient is permitted to move about freely during the waiting period.

Before the scan, the patient is instructed to urinate to ensure that the radioactive substance is not concentrated in the bladder. The individual lies on the back and may be repositioned to the side or stomach during the test. It is important for the patient to remain still during the procedure unless instructed to move.

During the scan, a machine with an arm–like device supporting the gamma camera passes over the body and records images of the radioactive material absorbed in the bones. This procedure does not cause discomfort and usually lasts between 30 and 60 minutes.

Sometimes a specific type of bone scan, called a triple–phase or three–stage bone scan, is performed. During this procedure, the scanning is performed at different times after the radioactive material is injected into the body. For instance, scanning may occur immediately after the injection, 20 minutes after injection and then two to four hours later.

In some cases, a type of radionuclide imaging scan called single-photon emission computed tomography (SPECT) may be performed to study a particular part of the body, such as the hips, lower back or jaw. This test may help a physician identify a problem more accurately.

After the test is completed, patients are instructed to drink plenty of fluids to ensure that any remaining radioactive substance exits the body. Radioactivity usually disappears within one to three days. Patients should not experience discomfort after the test. Women who are breastfeeding may be required to avoid nursing for 24 hours after the test.

The results of the scan are usually available within a few days or weeks. In general, the scan may reveal:

• Normal distribution. Areas where the radioactive substance has been distributed normally will appear uniform and gray throughout all the bones in the body.
  
  
• Hot spots. Areas where there is increased accumulation of the radioactive substance appear black on the scan. Hot spots may be caused by a fracture, bone cancer, infection, arthritis or other diseases such as Paget’s disease.
  
  
• Cold spots. Areas where there is a lack of radioactive substance appear light or white on the scan. Cold spots may be caused by a certain type of cancer (multiple myeloma) or lack of blood supply to the bone.

Few risks are associated with bone scans because the amount of radioactive material injected into the body is small. Some possible risks include:

• Women who are pregnant may pass radiation to the unborn child.
  
  
• Women who are breastfeeding may pass radiation to the child.
  
  
• Although these side effects are rare, some patients may develop a rash, swelling or severe allergic response (anaphylaxis).
  
  
• Though the risk is small, some patients may experience infection or bleeding due to the injection of radioactive substance.

A bone scan is not painful. Patients may feel minor discomfort when the contrast medium is injected or while holding a position during the test.

Although bone scans are useful in detecting abnormalities, they are less useful in diagnosing precise causes of the abnormality. Other diagnostic tests may be performed to identify conditions and diseases causing the unusual activity. For instance, if cancer is suspected, small amounts of bone tissue may be removed in a biopsy to confirm the diagnosis. The test results must be correlated with other information such as the patient’s clinical history and physical exam.

Other tests that may be performed along with a bone scan include:

• X-ray. Image of a body part, organ or system on film or fluorescent screens. It is produced by low doses of radiation.
  
  
• CAT scan (computed axial tomography). Test that allows for multiple x–rays to be taken from different angles around the patient. It creates images of organs and bones within the body. It may be performed alone or with the use of an injected dye (contrast medium).
  
  
• MRI (magnetic resonance imaging). Safe and noninvasive or minimally invasive imaging test that can help physicians diagnose diseases of numerous organs and vessels. It uses powerful magnets to produce images on a computer screen and film. As with a CAT scan, a contrast medium may be injected.

Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about bone scans:

1. Why is a bone scan being recommended for me?
   
   
2. Can injection of the radioactive substance into my body cause harm?
   
   
3. What do I need to do to prepare for a bone scan?
   
   
4. When and where will my bone scan be performed?
   
   
5. How long will I need to be there? Will I be able to leave the facility during the waiting period after my injection and before the scan?
   
   
6. Will I experience any pain from this test?
   
   
7. How long will it take for the radioactive substance to leave my body?
   
   
8. When will my test results be ready, and who will explain them to me?
   
   
9. What do the results of my bone scan mean?
   
   
10. What other types of tests might be required to help diagnose my condition?
    
    
11. If my test results show the need for treatment, what are my options, and which do you recommend?