Positron emission tomography is an imaging test used to diagnose and monitor cancer and other conditions. Commonly known as a PET scan, this test helps physicians to detect biochemical changes that may suggest the presence of cancer or other illnesses. The changes on a PET scan may appear before a patient exhibits visible symptoms. For cancer patients undergoing treatment, PET scans can identify how aggressive a cancer is and the extent of its metastasis (spread) to other parts of the body.
PET scans are performed using a scanning device that looks like a large doughnut. Patients are placed on a table and moved into the hole of the scanner. Within the scanner are multiple rings that detect changes in the body and produce images on a computer screen.
As part of the procedure, a form of slightly radioactive sugar is injected into the patient prior to the scan. The cells of the body absorb this sugar, which releases atomic particles called positrons. These positrons combine with electrons in the body to produce gamma rays. As gamma rays leave the body, they are detected by a special camera.
The images from the scanner contain varying colors or levels of brightness that help physicians identify abnormalities, such as the presence of cancer. For example, cancerous tissues use more energy and absorb more sugar than healthy tissues. For this reason, these malignant areas appear brighter than normal tissues on PET scan images. PET scans can also detect differences in both cancerous tissue and normal tissue that may have been damaged by cancer treatment.
PET scans are becoming more commonly used for studying cancer and its spread in the head and neck (including the brain), esophagus, breast, colorectal tract, ovaries and lungs. They may also be used to monitor lymphomas and melanoma. In some cases, PET scans may be used to diagnose or monitor other abnormalities, including those of the heart and brain.
A radiologist or other nuclear medicine expert examines the images from a PET scan and sends a report to the patient’s physician. Results usually are available within a few days of the scan. Depending on the results of this test, additional tests or treatment may be recommended. For patients with cancer, treatment methods may include chemotherapy, radiation therapy, surgery or other therapies.
PET scans are safe procedures that do not pose significant risks for most patients. The radioactive materials used are minimal and only remain in the body from a few hours to a few days. However, pregnant and breastfeeding women may be urged not to undergo a PET scan because of the potential for exposing a fetus or newborn to potentially harmful radiation. For many cancer patients, the benefits of the scan and the information it provides about the disease outweigh the associated risks.
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