PET and CT scans can be carried out for several different reasons. Some examples include the diagnosis of cancer and other illnesses; for evaluating the results of surgery or chemotherapy for cancer treatment; and for evaluating organ function after an event such as a heart attack. Sometimes these medical diagnostic procedures are carried out on people with symptoms such as unexplained abdominal pain, to try and determine what the cause might be.
A PET scan involves the use of nuclear imaging to create images of the body's interior organs and tissues. When you undergo this diagnostic procedure, you'll be given an intravenous injection of radioactive glucose, called fludeoxyglucose. After a waiting period of around one hour—to allow time for the glucose to be absorbed by the body's cells—it's time for the procedure itself. During a PET scan, sensitive imaging equipment is used to detect levels of the radioactive glucose in the body's cells. The more of the glucose that cells have absorbed, the brighter they appear on the PET images that are generated. The powerful computer attached to the PET scanner uses this information to generate a 3D image of the inside of the body, which is used for diagnosis and other purposes.
CT scans use x-ray technology, but take the idea a step further by taking multiple x-rays at the same time, from different angles around the body. Computer equipment attached to the CT scanner combines all of the x-rays to generate a 3D image of the body's interior. To prepare for a CT scan, you'll first be given an intravenous injection of a high-contrast coloured dye. This injection allows the CT scanner to create images with a higher level of detail than a normal x-ray can produce.
A CT and PET scan are often carried out simultaneously, using special equipment that performs both diagnostic tests at the same time. To prepare for the CT PET scan, patients are usually advised to eat a low carbohydrate diet the day before the procedure, and to avoid eating and drinking for at least six hours before the tests. Most people can continue to take medications as normal, with the exception of insulin. In total, this combination of diagnostic tests takes around three hours to complete, including the administration of glucose and contrast dye, and the following waiting period.
