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Home > Imaging Services
PET-CT
Your physician has ordered a PET-CT exam for you to learn more. We have compiled this information about your exam to better inform you and help answer your questions.
The PET-CT staff at all of our facilities is available to answer any additional questions you may have, so please do not hesitate to ask.
Overview of PET-CT Exam
Preparing for your PET-CT Exam
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Overview of PET-CT Exam
What is a PET Scan?A PET (positron emission tomography) scan creates an image of your body's metabolic activity and shows the rate at which your body's cells break down and use sugar (glucose).
This is done by injecting a small amount of radioactive material (FDG) into your blood stream and waiting for it to disperse to the area of focus. The PET scan is then performed to detect the radioisotope and creates an image on the computer screen.
PET is also useful in diagnosing certain cardiovascular and neurological diseases because it highlights areas with increased, diminished or no metabolic activity, thereby pinpointing problems.What is a CT Scan?A CT (computed tomography) scan is a noninvasive medical test that uses special x-ray equipment to produce multiple images or pictures of the inside of the body and a computer to join them together in cross-sectional views of the area being studied.
CT scans of internal organs, bone, soft tissue and blood vessels provide greater clarity than conventional x-ray exams.What is a PET-CT Scan?PET-CT is a relatively new diagnostic imaging exam that combines the functional information from a PET scan with the anatomical information from a CT scan. When a CT scan is superimposed over a PET scan, doctors can pinpoint the exact location of abnormal activity. They can also see the level and extent of that activity. Even when an abnormal growth is not yet visible on a CT scan, the PET scan may show the abnormal activity.Common usesPET-CT scans are commonly used to find changes in the body during the early stages of disease and for staging and restaging of cancers.
Safety - CTAs with other medical procedures, CT's are safe when used with care. Radiologists and x-ray technologists have been trained to use the minimum amount of radiation necessary to obtain the needed results. The amount of radiation used in most examinations is very small and the benefits greatly outweigh the risk of harm.
CT X-rays are produced only when a switch is momentarily turned on. As with visible light, no radiation remains after the switch is turned off.
Safety - PETBecause the doses of radiotracer administered are small, diagnostic nuclear medicine procedures result in minimal radiation exposure. Thus, the radiation risk is very low compared with the potential benefits.
Nuclear medicine has been used for more than five decades, and there are no known long-term adverse effects from such low-dose exposure.
Allergic reactions to radiopharmaceuticals may occur but are extremely rare.
Women should always inform their physician or technologist if there is any possibility that they are pregnant or if they are breastfeeding their baby.
PET exams also use x-ray-like radiation. But the method of use is quite different from x-rays and they produce very different looking images.
In nuclear medicine another precaution is advised for women who are breast-feeding a child. Some of the pharmaceuticals that are used for the study can pass into the mother's milk and subsequently the child will consume them. To avoid this possibility, it is important that a nursing mother inform her physician and the nuclear medicine technologist about this before the examination begins. Usually, you will be asked to discontinue breast-feeding for a short while, pump your breasts in the interim and discard the milk. Breast-feeding can often resume shortly afterwards.Preparing For Your PET-CT Exam
What should I expect BEFORE my PET-CT Exam?Medications
If you need to take your medication in the morning prior to the scan, take it with water. Most claustrophobic patients are able to tolerate a PET-CT or PET scan. Talk to your doctor if you think you need some additional anti-anxiety medication for the scan. We cannot prescribe or supply medication.
Food and drink
- Non-Diabetic: Do not eat or drink anything for at least 6 hours before the exam, except plain water. If your doctor has told you to take your regular medicine, take it with plenty of water.
- Diabetic: If you are diabetic, do not drink or eat anything for at least 4 hours prior to your scan. Take your diabetic medication as usual. If your doctor has told you to take your regular medicine, take it with plenty of water. Avoid: candies, gum or beverages other than water.
When to arrive
All patients are required to check in and register in the White 205 - Nuclear Medicine Reception area 30 minutes prior to scheduled exam time.
What to wear
Wear loose-fitting, comfortable clothes with no metal (zippers, under wire bras, etc) for the test. Leave your watch, jewelry, and other valuables at home.
Intravenous preparation
Many patients receive a contrast agent intravenously (IV) during their PET-CT test. If your doctor or the radiologist has determined that this procedure will enhance your PET-CT scan results, the technologist will place an IV in your arm or hand prior to going into the test (Please see the section on "Contrast Medium"). If you've ever had an allergic reaction to contrast, tell your doctor and the technologist. The doctor may prescribe special medicine for you to take before the exam and also while you are here for the exam. You should bring the last two doses of medicine with you.
Other information
- Do not exercise for at least 24 hours before the exam.
- Please leave pregnant family members and small children home.
- Pediatric patients are not scheduled for PET-CT.
What will I experience DURING my PET-CT Exam?Scanning
You will be required to lie flat with your arms raised above your head. If you think you will be unable to keep your arms above your head for approximately 35 minutes, please notify the technologist and they may accommodate you.
Length of scan
You should plan to be here for approximately 2-3 hours. The actual scanning and preparation time varies with the type of scan you are having.
Contrast medium
Contrast mediums, or contrast agents, highlight your organs and blood vessels and help the radiologist see them better. In the past, most contrast agents contained higher levels of iodine. The new contrast agents available today have lower iodine content, which greatly reduces the chance of an allergic reaction and most of the discomforts associated with the injection. The advantage of our state of the art scanners is that they maximize the efficiency of the contrast medium, which tends to dilute fairly quickly into your bloodstream. Since our scanners are so quick, it is possible to take all pictures while the contrast medium is still in a high concentration, which produces better images.
What should I expect AFTER my PET-CT Exam?
You can drive and resume normal activities immediately after leaving the department, unless you have taken medication to relax you. It is important that you drink as much water or fluids as possible for the rest of the day and empty your bladder as often as possible. This will result in a more rapid clearance of radioactivity and contrast from your body.
PET-CT Exam ResultsAll PET-CT exams are jointly read by two teams of Mass General radiologists trained in CT sub-specialty imaging and nuclear medicine.
Rapid results are essential not only for your peace-of-mind, but also for your physician to begin planning your treatment immediately, if necessary. After the scan has been read the results are sent to your physician, who will discuss them with you.
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Locations where PET-CT Exam is performed
How to Schedule a PET-CT ExamA referral from a physician is required for a PET-CT exam. Physicians may schedule patients using our online scheduling and report access program - ROE.
Additional Information and Resources
MGH Radiology Rounds E-Newsletter
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