After a radiopharmaceutical is administered to the patient, the target organ is localized and the radiation emitted from it can be detected by ____________

• A. Imaging instruments or gamma camera
• B. MRI scanner
• C. Ultrasound
• D. CT scanner

Answer: (A)

Radiopharmaceuticals emit gamma rays once they localize in the target organ, and those gamma photons are picked up by imaging instruments designed for nuclear medicine. The gamma camera is the classic detector used; it contains a scintillation crystal (like sodium iodide) that converts gamma rays into light, which a photomultiplier tube array turns into an electrical signal to form an image of tracer distribution. Other modalities don’t detect gamma rays—MRI relies on magnetic fields and hydrogen signals, ultrasound uses sound waves, and CT uses X-ray attenuation. Therefore, the emitted radiation is detected by imaging instruments such as a gamma camera.