This is an imaging modality that allows physicians to see diseases in one’s body. It utilizes a special dye that has a radioactive tracer. This tracer is injected into one's vein and after that distributed in the body where it’s absorbed by tissues and organs. It helps doctor s to see how well they are working. It measures oxygen use, glucose metabolism, blood flow, etc. It helps show problems at cellular level hence useful in detecting brain disorders, heart problems, central nervous system problems like seizure and memory disorders. It also shows the response to cancer to chemotherapy.