The Full form of PET is Positron Emission Tomography. PET scan is a type of imaging test that uses a radioactive substance called a tracer to look for disease in the body. A PET (Positron Emission Tomography) scan shows how organs and tissues are working. It is different than MRI and CT scans. These tests show the structure of, and blood flow to and from organs. Machines that combine the PET and CT images, called a PET/CT. A doctor may order a PET scan to inspect a person’s blood flow, oxygen intake, or the metabolism of organs and tissues. PET scans show problems at the cellular level, giving doctor the best view of complex systemic diseases. PET scans are most commonly used to detect heart problems, cancer, brain disorders, including problems with the central nervous system (CNS). PET scans show metabolic changes occurring at the cellular level in an organ or tissue. This is important because disease often begins at the cellular level. MRIs and CT scans can’t reveal problems at the cellular level. PET scans can detect very early changes in body cells. Detection of illness at the cellular level gives doctor the best view of complex systemic diseases, such as CAD (coronary artery disease), brain tumors, memory disorders, seizure disorders etc.