Technetium-99 (Tc-99) is a radioactive isotope of the element technetium. It is widely used in medical imaging, particularly in nuclear medicine, due to its ability to emit gamma rays. Tc-99 is produced from the decay of molybdenum-99, which is generated in nuclear reactors. Tc-99 has a half-life of about 6 hours, making it suitable for diagnostic procedures as it decays quickly, minimizing radiation exposure to patients. It is commonly used in scintigraphy to visualize organs such as the heart, bones, and kidneys, providing valuable information for medical diagnoses.