Why Can’t I Eat Before My PET Scan?
“When did you last eat or drink?” is a question you commonly hear the Nuclear Medicine technologists ask their PET (positron emission tomography) scan patients. Why is that so important? The radioisotope that is used in PET imaging, fluorine 18 fluorodeoxyglucose or 18F-FDG, is a glucose transporter. This radioisotope will go to any metabolically active areas in the body. If the glucose levels are elevated from food or drink the patient consumed prior to the test, the level of insulin will increase. When insulin levels increase, our muscles tend to “suck up” glucose to use in our daily activities. When the muscles take up the radiopharmaceutical, the radioactive tracer may not go to the areas the physicians are interested in seeing, rendering the exam suboptimal.
For ideal imaging we request that our PET scan patients have nothing to eat or drink for 4 hours prior to their scan and have a normal fasting glucose level. If the fasting glucose levels are too high or too low, we may need to reschedule the patient for another day to ensure that optimal images will be obtained. Medications can be taken prior to the exam with a minimal amount of water.
Some other exams in the Radiology Department also require the patient to refrain from eating or drinking prior to an appointment. Please feel free to ask us why — we are happy to explain the difference this can make in our studies, and we want to give you the best possible images and outcome.
Contributed by Kyaira Walton, (Spec Tech-Nuc Med) and edited by Janet Adams, (Adv Tech-Ult).