Bone Scan

A bone scan involves imaging the skeleton by a scanning camera after I.V. injection of a radioactive tracer compound. The tracer of choice, radioactive technetium diphosphonate, collects in bone tissue in increased concentrations at sites of abnormal metabolism. When scanned, these sites appear as "hot spots" that are often detectable months before an X-ray can reveal any lesion. To promote early detection of lesions, this test may be performed with a gallium scan.

Purpose

• To detect or to rule out malignant bone lesions when radiographic findings are normal but cancer is confirmed or suspected
• To detect occult bone trauma due to pathologic fractures
• To monitor degenerative bone disorders
• To detect infection
• To evaluate unexplained bone pain

Patient preparation

• Describe the procedure to the patient. Explain that this test may detect skeletal abnormalities sooner than is possible with ordinary X-rays.
• Because the patient is required to drink 4 to 6 glasses of water or tea in the interval between injection of the tracer and the actual scanning, advise him not to drink large amounts of fluids before the test.
• Tell him who will perform the test and where and that he may have to assume various positions on a scanner table. Emphasize that he must keep still for the scan.
• Assure the patient that the scan itself, which takes about 1 hour, is painless and that the isotope, although radioactive, emits less radiation than a standard X-ray machine.
• Make sure the patient or a family member has signed a consent form.
• If a bone scan is ordered to diagnose cancer, evaluate the patient's emotional state and offer support.
• Administer prescribed analgesics.
• After the patient receives an I.V. injection of the tracer and imaging agent, encourage him to increase his intake of fluids for the next 1 to 3 hours to facilitate renal clearance of the circulating free tracer.

Equipment

Bone mineral tracer, 3-ml syringe, 21G needle, 70% alcohol or povidoneiodine solution, sterile sponge, tourniquet, scanning camera

Procedure and posttest care

• Instruct the patient to void immediately before the procedure; then position him on the scanner table.
• As the scanner head moves back and forth over the patient's body, it detects low-level radiation emitted by the skeleton and translates this into a film or paper chart, or both, to produce two­dimensional pictures of the area scanned.
• The scanner takes as many views as needed to cover the specified area. The patient may have to be repositioned several times during the test to obtain adequate views.
• Check the injection site for redness or swelling. If a hematoma develops, apply warm soaks.
• Don't schedule any other radionuclide tests for 24 to 48 hours.

Precautions

• To avoid exposing the fetus or infant to radiation, a bone scan is contraindicated during pregnancy or lactation.
• Allergic reactions to radionuclides may occur.

Normal findings

The tracer concentrates in bone tissue at sites of new bone formation or increased metabolism. The epiphyses of growing bone are normal sites of high concentration, or hot spots.

Abnormal findings

Although a bone scan demonstrates hot spots that identify sites of bone formation, it doesn't distinguish between normal and abnormal bone formation. But scan results can identify all types of bone malignancy, infection, fracture, and other disorders, if viewed in light of the patient's medical and surgical history, X-rays, and other laboratory tests.

Interfering factors

• Failure to observe pretest restrictions
• Distended bladder (possible obscuring of pelvic detail)
• Improper injection technique (possible seepage of tracer into muscle tissue, creating false hot spots)
• Antihypertensives (invalidate test results)