A positron emission tomography scan, also known as a PET scan, is a non-invasive imaging test that uses a radioactive tracer to reveal various diseases in the body. PET scan results are generally only interpreted by radiologists who have received specialized training in nuclear medicine — a type of medicine that uses small amounts of radioactive substances, called radiotracers or radiopharmaceuticals. After such analysis, radiologists usually forward the PET scan results to the ordering physician, who then typically reviews them with the patient.
In order to prepare for a PET scan, a patient must first receive a radiotracer. Depending on a variety of circumstances, this can either be given to the patient intravenously, as an inhaled gas, or as a drinkable liquid. Once the radiotracer settles in the area to be imaged, it emits a certain type of energy known as a gamma ray. A gamma camera, PET scanner, and probe measure the gamma rays. A computer then helps to determine how much radiotracer is being absorbed by those areas. The computer also takes pictures of the targeted areas, which indicates its structure and functioning ability, including blood flow, oxygen usage, and glucose metabolism.
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When a radiologist interprets PET scan results, he or she may be able to identify several different diseases, including cancer, as the test typically highlights the most rapidly growing cells in the body. These conditions light up as hot spots on the images that the radiologist can see on a computer. The activity of such spots is usually expressed in Standardized Uptake Value (SUV), which help the radiologist interpret the scan results. Generally speaking, cancer will have an SUV of over 2.5, though there are a variety of other factors that may influence how a radiologist interprets any given hot spot. These factors can include the location of the suspected cancer, the patient's history, and other imaging results.
PET scan images can be combined with computed tomography (CT) images or magnetic resonance imaging (MRI) in a process called co-registration or image fusion. Most PET scans are currently combined with CT scans to create images that provide detailed anatomical information about the organs and tissues. Results from PET/CT scans typically give more accurate diagnostic and treatment information than PET scan results alone. PET and PET/CT scans are most commonly used to help diagnose and re-stage cancer, evaluate the heart muscle, and detect brain abnormalities. In all cases, interpreting PET/CT or PET scan results can be a very complicated process and should generally be reserved for physicians and radiologists who have received specialized training in nuclear medicine.