Positron emission tomography (PET) is a medical imaging technique that visualizes metabolic and biochemical processes in the human body. It involves injecting a small amount of radioactive material (radiotracer) into the patient, which emits positrons. When positrons collide with electrons, they produce gamma rays, which are detected by a PET scanner. The resulting images provide detailed information about organ function, aiding in the diagnosis and monitoring of various diseases, including cancer.