Which radiopharmaceutical is primarily used in bone scans?

• A. Fluorine-18
• B. Gallium-67
• C. Tc HDP and Tc MDP
• D. Indium-111

Answer: (C)

Technetium-99m labeled compounds, specifically Technetium diphosphonates such as Tc HDP (hydroxymethylene diphosphonate) and Tc MDP (methylene diphosphonate), are the primary radiopharmaceuticals used in bone scans due to their high affinity for bone tissue. These compounds are particularly effective for imaging because they localize in areas of increased osteoblastic activity, which is often present in conditions such as metastatic disease, inflammation, or trauma.

The biodistribution of Tc HDP and Tc MDP allows for detailed visualization of bone metabolism and integrity. They emit gamma rays that can be detected by gamma cameras, making them ideal for the non-invasive assessment of various bone pathologies. This targeting of bone helps clinicians evaluate conditions ranging from benign bone diseases to malignancies, thereby aiding in diagnosis and treatment planning.

In contrast, other radiopharmaceuticals listed, although useful in their respective applications, do not primarily serve the purpose of imaging bone. Fluorine-18, for example, is more commonly used in Positron Emission Tomography (PET) imaging for metabolic evaluation, while Gallium-67 is utilized for detecting tumors and infections. Indium-111 is primarily employed in