What is PET? PET (or positron emission tomography) is a medical imaging tool which assists physicians in detecting disease. Simply stated, PET scans produce digital pictures that can, in many cases, identify many forms of cancer, damaged heart tissue, and brain disorders such as Alzheimer's, Parkinson's, and epilepsy. Technically, PET is a medical imaging technology that images the biology of disorders at the molecular level before anatomical changes are visible. A PET scan is very different from an ultrasound, X-ray, MRI, or CT, which detect changes in the body structure or anatomy, such as a lesion (for example, a sizeable tumor) or musculoskeletal injury. A PET scan can distinguish between benign and malignant disorders (or between alive and dead tissue), unlike other imaging technologies which merely confirm the presence of a mass. A PET scan can detect abnormalities in cellular activity generally before there is any anatomical change. A PET scan can, in many cases, identify diseases earlier and more specifically than ultrasound, X-rays, CT, or MRI. PET can also help physicians monitor the treatment of disease. For example, chemotherapy leads to changes in cellular activity and that is observable by PET long before structural changes can be measured by ultrasound, X-rays, CT, or MRI. A PET scan gives physicians another tool to evaluate treatments, perhaps even leading to a modification in treatment, before an evaluation could be made using other imaging technologies. How PET Works When disease strikes, the biochemistry of your tissues and cells change. In cancer, for example, cells begin to grow at a much faster rate. A PET scan takes a digital picture of abnormal cellular structure. The most common form of a PET scan begins with an injection of a glucose-based radiopharmaceutical (FDG), which travels through the body, eventually collecting in the organs and tissues targeted for examination. The patient lies flat on a bed/table that moves incrementally through the PET scanner. The scanner has cameras that detect the gamma rays emitted from the patient, and turns those into electrical signals, which are processed by a computer to generate the medical images. The bed/table moves a few inches again, and the process is repeated. This produces the digital images, which are assembled by the computer into a 3-D image of the patient's body. If an area is cancerous, the signals will be stronger there than in surrounding tissue, since more of the radiopharmaceutical (FDG) will be absorbed in those areas.