Bone Scan (Scintigraphy): What It Is and Applications

Bone scans, also known as bone scintigraphy, are a powerful diagnostic tool used to explore the structure of the skeleton and detect any vascular and metabolic alterations in the bones. This post provides an understanding of bone scans, including what they entail, their benefits, potential risks, and how they're performed.

What Are Bone Scans?

Bone scans leverage radioactive drugs, specifically technetium-99m labeled diphosphonates, that deposit at the bone level, reflecting the blood supply and the metabolic behavior. This behavior is determined by the activity level of osteoblasts, cells specialized in bone tissue synthesis.

The emitted radiation from the skeleton, proportional to the concentration of the radioactive drug, allows for the capture of detailed images and evaluation of any vascular and metabolic changes. The higher the blood flow and metabolism of a specific bone region, the greater the concentration of the tracer.

It's important to note that bone scans are highly sensitive, but nonspecific. They can't reveal the nature of the detected pathology. Hence, they're often used in conjunction with radiological examinations or other imaging methods like magnetic resonance imaging.

The Applications of Bone Scans

Bone scans are instrumental in identifying and monitoring primary skeletal tumors and bone metastases, which are distant localizations of a malignant tumor. Due to their ability to detect anomalies at an early stage, bone scans are performed immediately after the diagnosis of tumors most statistically correlated to secondary bone localizations.

Additionally, bone scans are useful in recognizing inflammatory osteo-articular pathologies, microfractures, necrosis of the femoral head, osteomyelitis, pain in orthopedic prostheses, pain assessment in patients with normal radiography, algoneurodystrophies, and assessment of the vitality of bone implants.

Are Bone Scans Painful or Risky?

Bone scans are generally simple and painless procedures, although the radiopharmaceutical must be administered intravenously. The doses of isotope administered are very low and do not pose significant risks to the patient. However, the use of the scintigraphic technique is contraindicated during pregnancy.

Additionally, for women of childbearing age, the scan is usually performed within ten days following the start of the last menstruation to exclude the risk of an ongoing pregnancy. During breastfeeding, some radioactive substances can pass into breast milk, so the scan may be postponed or performed subject to the suspension of breastfeeding.

The tracers used are not contrast agents and do not cause any disturbance or allergic reactions. Bone scans can also be performed on children, with the amount of drug used proportional to body weight. They can be repeated over time to evaluate the course of a disease.

How is a Bone Scan Performed?

The examination begins with a preliminary visit aimed at investigating the clinical history, the use of particular drugs, and any documentation on the current pathology. Metallic objects must be removed to avoid interference with the diagnostic procedure.

The radiopharmaceutical is then administered intravenously. Depending on the technique used, some initial images may or may not be detected. After this initial phase, it's necessary to wait three to four hours to allow the radiopharmaceutical to fix in the bones.

During this waiting period, the patient should drink at least half a liter of water to facilitate the elimination of unabsorbed radioactivity. It's also crucial to empty the bladder frequently, even before the scan itself, as a full bladder can obstruct the examination of the pelvic bones.

The actual exam takes place two to three hours after the injection and lasts about 15 to 30 minutes. The total time for the examination is approximately four hours, although this can vary based on the patient's clinical needs.

No special preparations are required before a bone scan. However, good hydration can improve image quality. After the scan, the patient can resume normal activities without any particular precautions, although it's recommended to drink more fluids to facilitate the elimination of the radiopharmaceutical.

In summary, bone scans are a valuable diagnostic tool in the medical field, providing detailed images of the skeleton and helping to detect various bone-related conditions. While they involve exposure to a low dose of radiation, the benefits of early detection and diagnosis often outweigh the potential risks.