What is the most commonly used nuclide in nuclear medicine?

• A. Ga-67
• B. I-131
• C. Xe-133
• D. Tc-99m

Answer: (C)

Technetium-99m is preferred because it combines imaging quality with practical on-site availability. Its gamma photon energy of about 140 keV is ideal for detection by standard gamma cameras, and its half-life of roughly 6 hours provides enough time to perform the scan while keeping radiation exposure relatively low. Crucially, Tc-99m is produced from a Mo-99/Tc-99m generator, making it widely accessible at many centers without needing an on-site reactor. Its chemistry is highly versatile, allowing it to be bound to a variety of compounds that target different organs—bone, heart, kidneys, brain, biliary system, and more—so a single radionuclide can support many imaging studies. While other nuclides like Ga-67, I-131, or Xe-133 have their specialized uses, Tc-99m’s combination of suitable energy, short half-life, and broad applicability makes it the workhorse of diagnostic nuclear medicine.