A PET scanner, or Positron Emission Tomography scanner, is a medical imaging device that helps doctors see how organs and tissues are functioning in the body. It works by using a small amount of radioactive material, which is injected into the patient. This material emits positrons, and when they collide with electrons in the body, they produce gamma rays that the scanner detects. The images produced by a PET scanner can reveal areas of abnormal activity, making it useful for diagnosing conditions like cancer, heart disease, and brain disorders. It is often used in combination with other imaging techniques, such as CT scans or MRI, to provide a more comprehensive view of a patient's health.