Which of the following is NOT a radiopharmaceutical used for bone scans?

The reason why CT scan dye is not a radiopharmaceutical used for bone scans lies in its fundamental purpose and composition. CT scan dyes, or contrast agents, are primarily used to enhance the visibility of structures within the body during computed tomography imaging. These dyes help differentiate between various tissues but do not have the specific targeting properties that radiopharmaceuticals have.

In contrast, the other options listed are all radiopharmaceuticals specifically designed for bone scans. F-18 sodium fluoride, MDP medronate, and HDP oxidronate are radionuclides that localize in bone tissue, allowing for the visualization of bone metabolism and pathology. These substances are utilized in nuclear medicine to detect conditions such as fractures, infections, and tumors in the bone.

Therefore, the distinction between a radiopharmaceutical and a contrast agent clarifies why CT scan dye does not categorize as a radiopharmaceutical used for bone scans.