Nuclear medicine is a field of medicine that diagnoses or treats the body's condition and diseases safely and comfortably by using trace amounts of radioactive isotopes that emit radiation as tracers. In-vivo imaging is performed using gamma cameras or Positron Emission Tomography (PET/CT) to visualize the distribution of radioactive tracers injected into the body for the diagnosis of various diseases such as tumors, brain disorders, heart disease, endocrine disorders, and bone diseases.