What is PET/CT Imaging?
PET/CT imaging is the combination of two distinct imaging techniques.
What is PET Imaging?
PET, or positron emission tomography, is a look at the metabolic or biochemical activitypresent in a given anatomical region using radiotracers.
What is a radiotracer?
A radiotracer is a chemical compound in which atoms have been replaced by a radionuclide. After undergoing normal radioactive decay, the path the radiotracer takes can be traced, from reactants to products. Essentially, a radiotracer allows for the visualization of chemical processes within the body. Radiotracers of carbon, phosphorus, nitrogen, oxygen, fluorine, and sulfur are the most common.
What is CT imaging?
Computed tomography, or CT, imaging combines X-ray images taken of the body at different angle to create cross sectional images of the bones, blood vessels, and soft tissues inside the body. CT scans allow medical professionals to view parts of the body in individual slices.
Is FDG PET specific for cancer?
No, it is a marker of metabolism. In general, any disease that causes increased metabolism can result in increased FDG uptake and mimic malignancy.
What examples of benign etiologies can cause increased FDG activity?
Physiologic processes, infections, inflammation, and granulomatous diseases.
What factors will affect FDG uptake?
Blood glucose and insulin levels, FDG uptake time, and other variables, such as recent exercise and brown fat activity.
Why are patients asked to fast?
To decrease blood glucose and insulin levels that will result in more uptake in tumors, as well as, decrease the amount of cardiac activity present on a scan. When patients fast longer than a few hours, the myocardium will begin to utilize fatty acids rather than glucose (and FDG) for generating energy.
What is an attenuation correction artifact?
These are artifacts that are observed only on the attenuation corrected PET images. They are not observed on non-attenuation corrected images. These are seen less frequently on current scanners. These are caused during the attenuation correction process that uses the CT on PET/CT scanners and occur in areas of high attenuation material with high Hounsfield numbers. Examples of materials that reportedly cause attenuation correction artifacts are orthopedic devices, chemotherapy ports, dense barium, and dental amalgam.
Is it possible to scan diabetic patients?
Yes. However, it is important to have their glucose levels at close to normal levels. At the time of scheduling the diabetic patient for the PET/CT scan, it should be confirmed that the patient’s blood glucose level will be less than 200 mg/dl at the time of the FDG administration. The patient should not have received regular insulin within 4 hours of the time of the FDG administration. If the patient arrives at the PET facility and the blood glucose is above a certain level (for example, above 200mg/dl), some centers reschedule the patient. If it is not convenient to reschedule the patient, some centers go ahead and do the study. A caveat should appear in the report that the study may be less accurate because of the abnormal blood sugar level. Oral therapies and long acting insulin can usually be continued; however, some patients cannot continue the oral diabetic therapy and fast for 4 hours without becoming hypoglycemic.
What should I expect during the exam?
You will receive a small injection of FDG (sugar water with a radioactive tracer). You will sit or lie down on a comfortable chair or bed for 30 to 90 minutes while the FDG travels throughout your body. After this time, the technologist will assist you to the scanner. The CT portion of the exam is completed first, followed by the PET portion. You may be asked to hold your breath for several seconds while the CT scan is performed. It is important that you don't move for the duration of the exam. When the total scan is finished, the computers will produce images for the radiologist to review.
How do I find out the results?
The reading radiologist will interpret the images and provide a written report to your referring physician. Your referring physician will contact you to share the results.
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Question about Your Exam?
If you have a question about your exam, please call our department at (530) 529-8280.