Common positron-emitting radionuclides include which of the following?

• A. Sodium, potassium, calcium
• B. Hydrogen, Helium, Neon
• C. Oxygen, carbon, nitrogen, rubidium, gallium, copper, fluorine
• D. Oxygen, carbon, nitrogen

Answer: (C)

Positron-emitting radionuclides are used in PET imaging because their decay produces positrons that annihilate with electrons, yielding two 511 keV photons detected by the scanner. The most commonly used PET radionuclides include fluorine-18, carbon-11, nitrogen-13, oxygen-15, and other clinically important examples such as rubidium-82, gallium-68, and copper-64. This set—oxygen, carbon, nitrogen, rubidium, gallium, copper, and fluorine—covers the major isotopes routinely employed in PET, making it the best match. While some isotopes of sodium, potassium, and calcium exist, they are not standard positron-emitting tracers in routine PET practice, and hydrogen does not have a widely used positron-emitting isotope in clinical use.