Tc-99m, or Technetium-99m, is a radioactive isotope commonly used in medical imaging. It emits gamma rays, which can be detected by special cameras to create detailed images of organs and tissues in the body. This makes it valuable for diagnosing various conditions, including heart disease and cancer. The isotope has a short half-life of about six hours, meaning it decays quickly and minimizes radiation exposure to patients. Tc-99m is typically produced in a molybdenum-99 generator and is favored for its ability to provide high-quality images while being relatively safe for patients.