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 to create detailed images. These images can help diagnose various conditions, including cancer, heart disease, and brain disorders. By showing how well certain areas of the body are working, a PET scan can provide valuable information that other imaging techniques, like CT scans or MRI, may not reveal.