Bone scintigraphyMedical editor Trond Bogsrud MD
Oslo University Hospital
Bone scintigraphy is one of the most common nuclear medicine investigations. The investigation is particularly useful because images of the skeleton can be taken from head to toe, or back to front, by a relatively simple procedure.
The investigation is highly sensitive for showing unhealthy processes in the skeleton but the specificity is proportionately low. It is especially sensitive for active, sclerotic tumors.
- Small, osteolytic tumors, metastases, especially in plasmacytoma, but also in malignant melanomas, kidney cancer, and thyroid cancer, can be overlooked
- For bone pain and “negative” bone scan, an MRI should be performed
- In patients with treatment response from bone metastases, one will usually see an increase in uptake of metastases after 3 months after start of effective treatment. This is a sign of healing.
- Radiation induced insufficiency breaks should not be interpreted as metastases
- MRI is more sensitive and specific for finding bone metastases in the spine and pelvis. But MRI is much more resource-demanding, therefore a bone scan will often be the first choice.
Sources of error
- False negative bone scan occurs with myelomatose and in osteolytic metastases
- Apparent outbreak of bone metastases can occur in conjunction with treatment despite clinical improvement (flare phenomenon)
- Stage grouping of cancer with a tendency for bone marrow and bone metastases
- Primary bone tumor
- Unclear bone pain in patients without known cancer disease
- Sclerotic tumors for example bone metastases from prostate cancer, breast, or lung
- To diagnose primary tumors or relapse
- The patient should be well hydrated.
- Loose metal objects such as jewelry and coins should be removed.
- Radiopharmaceutical 99mTc bisphosphonate complex is given. In Norway, the most widely used complex for this procedure is methylene bisphosphonate, MDP.
- The 99mTc bisphosphonate complex is injected intravenously. 99mTc-labelled bisphosphonate binds to the osteoblasts, especially in the areas with high perfusion and high osteoblast activity.
- In dynamic image taking for assessment of blood supply and vascularization, images are taken during injection of the radiopharmaceutical drug.
- Static images of the whole body or parts of the body are taken around 2.5 hours after the injection.
- Between injection and image taken, the patient should drink copious amounts of water (about 1 liter) and eliminate as often as possible to reduce radiation exposure in the bladder.
- The bladder should be empty before image capture. (Around 50% of injected activity is eliminated via the kidney in the urine during the first hours.
- With a one-head camera, the whole body test takes around 30 minutes.
- With a two-head camera, the whole body test takes around 50 minutes.
- It is important that the patient remains completely still during the test. If the patient is unable to lie still for at least 20 minutes, multiple images can be taken instead of one whole body scan.
- It can be necessary to supplement image taking with individual images using special angles (3-10 minutes per image).
- The patient should continue to drink lots of water for the rest of the day after the test, as the radioactivity is eliminated via the kidneys.
- The radiation exposure to persons in contact with the patient is insignificant, but the patient should still avoid extended contact with children and pregnant mothers the day of the test.
- The result of the test is often available the following day.