This document summarizes the use of gamma rays in biomedical imaging. It describes gamma rays as high-energy electromagnetic radiation produced during nuclear decay. The main uses of gamma rays in medicine are sterilization, cancer treatment, and diagnostic imaging techniques like scintigraphy, PET, and SPECT. These techniques use gamma-emitting radioisotopes and gamma cameras to construct 2D and 3D images of internal body structures. While gamma rays are useful medically, they can also damage cells and tissues if a person is exposed to high doses. The sievert and rem are units used to measure the biological effects of gamma ray exposure.