A bone scan is performed primarily to evaluate and monitor persons with known or suspected metastatic disease. Breast cancer, prostate cancer, lung cancer, and lymphoma tend to metastasize to bone. Bone images visualize lesions 6–12 months before they appear on x-rays. A bone scan may also be performed to evaluate patients with unexplained bone pain, primary bone tumors, arthritis, osteomyelitis, abnormal healing of fractures, fractures, shin splints, or compression fractures of the vertebral column; to evaluate pediatric patients with hip pain (Legg–Calvé–Perthes disease); and to assess child abuse, bone growth plates, sports injuries, and stress fractures. It is also performed to determine the age and metabolic activity of traumatic injuries and infections.

Other indications are evaluation of candidates for knee and hip prostheses, diagnosis of aseptic necrosis and vascularity of the femoral head, presurgical and postsurgical assessment of viable bone tissue, and evaluation of prosthetic joints and internal fixation devices to rule out loosening of prosthesis or infection.

Bone scanning has greater sensitivity in the pediatric patient than in the adult and is used for early detection of trauma. Normally, there is increased activity in the growth plates of the long bones. The child’s history is significant for correlation and diagnostic differentiation. In older children with unexplained pain who participate in sports, stress fractures are often found on a bone scan.

A bone-seeking radiopharmaceutical is used to image the skeletal system. An example is ^99mTc-labeled phosphate injected intravenously. Imaging usually begins 2–3 hours after injection. Abnormal pathology, such as increased blood flow to bone or increased osteocytic activity, concentrates the radiopharmaceutical agent at a higher or lower rate than the normal bone does. The radiopharmaceutical agent mimics calcium physiologically; therefore, it concentrates more heavily in areas of increased metabolic activity.

1. Inject radioactive ^99mTc methylene diphosphonate intravenously.

2. A 2- to 3-hour waiting period is necessary for the radiopharmaceutical agent to concentrate in the bone. During this time, the patient may be asked to drink 4–6 glasses of water.

3. Before the imaging begins, ask the patient to void because a full bladder masks the pelvic bones.

4. Imaging takes about 30–60 minutes to complete. The patient must be able to lie still during the scan.

5. Additional spot views of a specific area or three-dimensional SPECT imaging may be requested by the healthcare provider.

6. See Chapter 1 guidelines for safe, effective, informed intratest care.

Abnormal concentrations indicate the following:

1. Very early bone disease and healing are detected by nuclear medicine bone images long before they are visible on x-rays. X-rays are positive for bone lesions only after 30%–50% decalcification (decrease in bone calcium) has occurred.

2. Many disorders can be detected but not differentiated by this test (e.g., cancer, arthritis, benign bone tumors, fractures, osteomyelitis, Paget disease, aseptic necrosis). The findings must be interpreted in light of the whole clinical picture because any process inducing an increased calcium excretion rate will be reflected by an increased uptake in the bone.

3. For patients with breast cancer, the likelihood of a positive bone image finding in the preoperative period depends on the staging of the disease, and imaging tests are recommended before initial therapy. Stages 1 and 2: 40% have a positive bone image. Stage 3: 19% have a positive bone image. Yearly nuclear medicine bone imaging is recommended for follow-up.

4. Multiple myeloma is the only tumor that shows better detectability with a plain x-ray than a radionuclide bone procedure.

5. Multiple focal areas of increased activity in the axial skeleton are commonly associated with metastatic bone disease. The reported percentage of solitary lesions due to metastasis varies on a site-by-site basis. With a single lesion in the spine or pelvis, the cause is more likely to be metastatic disease than with a single lesion occurring in the extremities or ribs.

Pretest Patient Care

1. Instruct the patient about the purpose and procedure of the test. Alleviate any fears concerning the procedure. Advise the patient that frequent drinking of fluids and activity during the first 6 hours help to reduce excess radiation to the bladder and gonads.

2. The patient can be mobile and active during the waiting period. There are no restrictions during the day before imaging.

3. Remind the patient to void before the scan. If the patient is in pain or debilitated, offer assistance to the restroom.

4. Order and administer a sedative to any patient who will have difficulty lying quietly during the imaging period.

5. Refer to standard NMI pretest precautions. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

1. False-negative bone images occur with multiple myeloma of the bone. When this condition is known or suspected, the bone scan is an unreliable indicator of skeletal involvement.

2. Patients with follicular thyroid cancer may harbor metastatic bone marrow disease, but these lesions are often missed by bone scans.

Normal

Homogeneous distribution of radiopharmaceutical agent