A PET (positron emission tomography) scan is an imaging test that creates 3D pictures of the inside of the body. It uses a mildly radioactive drug called a tracer to show areas of the body where cells are more active than normal. The tracer is usually FDG (fluorodeoxyglucose), a modified form of glucose that gets absorbed by tissues. When tissues absorb a lot of glucose, it may indicate a cancerous tumor. The PET scan can help diagnose and monitor a variety of conditions, including cancer, heart disease, and brain disorders. It can also help to find out where and whether cancer has spread. PET scans are sometimes used to look for cancer in the lymph nodes in the center of the chest. PET scans can be used to check certain brain disorders, such as tumors and Alzheimers disease. PET scans are usually done in the radiology or nuclear medicine department as an outpatient. The scan usually takes about 15 to 30 minutes to produce detailed images of metabolic activity in the tissues and organs. PET scans are safe for most people, but like any medical test, they carry some risks. PET scans must be interpreted carefully because noncancerous conditions can look like cancer, and some cancers do not appear on PET scans.