General PET/CT Scan FAQs
A PET/CT scan is a type of advanced diagnostic imaging test. It combines a PET Scan and a CT scan with both exams done at the same time. The PET scan maps out where tracers go to show cells in the body that are overactive. The most common type of PET scan is used to assess the rate of sugar use in cells in the body. Abnormal cells such as cancer grow more rapidly and use more sugar for energy. Normal cells and scar tissue use very little or no sugar in comparison.
For the PET scan, you will be injected with a special sugar called FDG. It is radioactive so that it can be seen using the PET scanner. The scanner will create a 3-D map of your body which will be used by a Nuclear Medicine specialist to answer your doctor’s specific question.
The PET portion of the study is combined with a CT scan and is done to localize the FDG to particular body parts and adjust for different body shapes.
Modern PET/CT scanners are so advanced that the time for a PET scan has been significantly reduced in recent years. Although PET scans used to take an hour or more, our machine still takes an average of 30-45 minutes on almost all PET scans. The Scan time can vary slightly based upon the patient height (taller patients require a few more minutes) and the region of interest. Eg. brain scan or whole-body scans.
The technologist is responsible for greeting you, performing the PET scan itself, obtaining the highest quality PET images possible, and of course, making sure you are comfortable throughout the entire process. Once complete, a Consultant Nuclear Medicine Physician or specialty-trained PET radiologist will view your images on a dedicated workstation, compare your images to any prior studies, generate a written report and transmit this report to your ordering Oncologist.
In general terms, a CT scan only evaluates the anatomical structures of your body. PET adds vital functional information that, when combined with CT, markedly improves diagnostic capabilities. This leads to far more accurate diagnosis and staging, which ultimately results in better care.
No. The PET/CT scan requires the administration of a radioactive isotope. For this reason, portions of the office are restricted and can only be occupied by the patient and the authorized medical personnel.
As with most other medical imaging tests, PET scans involve a small amount of what we call “diagnostic levels” of radiation. Your Oncologist has ordered a PET scan because he or she feels the benefits of the scan far outweigh any small risks associated with low levels of diagnostic “X-rays”. Also, our PET scanners are capable of obtaining very high-quality scans with relatively less radiation compared to the older machines.
No, a PET/CT scan is a test used to diagnose disease, not provide treatment. The results of a PET/CT scan help your Oncologist determine their treatment decisions.
Although FDG is very similar to glucose, the amount injected is so small it will not affect your blood glucose level.
The PET/CT scan is so sensitive that it can even be affected by eye motion, head motion, or stimulation during the “uptake phase”, which is the time period immediately following your injection. Although this may lead to some boredom, the recommendation is for you to rest quietly in a dimly lit room during this ‘uptake phase’ after injection in order to obtain the best possible image quality.
PET/SCAN Preparation FAQs
Yes, please inform the Technologist if you ate within the last 4 hours so it can be noted on the chart. PET/CT scans use a sugar-based agent to provide very high quality and detailed images. In order to work correctly, our agent must distribute on its own. If you have any calories, such as sugar, within that four-hour timeframe, that will compete with our agent and significantly change the results of your test. Ultimately, this could affect your diagnosis and treatment.
However, we understand that accidents happen! If for any reason you do eat or drink anything other than water within this timeframe, please let us know. We would be happy to reschedule you in order to obtain the best possible images, which will lead to better care. Call us if you have any more questions.
Yes, please inform the Technologist if you ate within the last 4 hours so it can be noted on the chart. PET/CT scans use a sugar-based agent to provide very high quality and detailed images. In order to work correctly, our agent must distribute on its own. If you have any calories, such as sugar, within that four-hour timeframe, that will compete with our agent and significantly change the results of your test. Ultimately, this could affect your diagnosis and treatment.
However, we understand that accidents happen! If for any reason you do eat or drink anything other than water within this timeframe, please let us know. We would be happy to reschedule you in order to obtain the best possible images, which will lead to better care. Call us if you have any more questions.
PET/CT scan days: Expected sequence of the events
You will arrive and be interviewed by our Technologist. The Technologist will ask you the dates that you have had any surgeries or biopsies within the last three months, or of any Chemotherapy or Radiotherapy. The Technologist will explain the test and get your permission to do it. They will measure your height and weight and check your blood sugar with a finger prick before the injection. If you have brought medicine for claustrophobia, the Technologist will tell you when to take it.
If your scan requires oral contrast, the Technologist will tell you when to drink the second bottle.
For women of child-bearing age, the Technologist will make sure that you are not pregnant or breastfeeding. A pregnancy test may be needed if not sure.
The Technologist will start an IV in your arm and inject the FDG. You will stay quietly in a room by yourself for one hour to allow the FDG to travel throughout your body. We want you to rest quietly without moving, talking or chewing so that the test is accurate. You can continue to drink plain water. If you must empty your bladder, wait at least 30 minutes after the injection before going to the washroom. You should not use your cell phone during this hour. If you came with a friend or family member, they will not be able to stay with you during this hour.
Near the end of the hour, we will ask you to use the washroom to empty your bladder. This is done to remove excess activity in the bladder, as FDG is excreted through the urine.
The Technologist will then move you into the scanner. You will lie down on your back on the bed of the scanner. Your arms will be above your head if possible. You will be asked to keep still for the scan. The bed will move you through the scanner while the pictures are taken. The Technologist will watch you during the entire scan. The scan will take up to 40 minutes. Occasionally, extra pictures may be required but not typically. You will then be moved off the bed and will be free to go. If you came with a family member or friend, they could rejoin you now.
Drink a lot of fluids that day to rinse the FDG out of your body. You may now return to your normal diet and exercise level.
A report of the results of your scan will be sent to your physician.
Information for Diabetic patients undergoing the PET/CT scan at IMIC
If your blood sugar is above 10 mmol/l on the scan day, we will get a poor-quality scan and you may have to be rescheduled.
Notify us in advance of your appointment if you typically have difficulty keeping blood sugar at or below 10 mmol/l, or if your diabetes is poorly controlled, or if you are on continuous insulin infusion.
If you take your insulin or diabetes pills too near the FDG injection time, there shall be diffuse distribution of FDG in the muscles instead of where we need it.
Do not take any diabetes medicines or eat within four hours of your appointment time.
Watch your diet carefully the day before your scan. Check your blood sugar often and try to keep it below 10 mmol/l (180 mg/dl) or ideally below 8.3 mmol/l (150 mg/dl).
Bring a list of all your medications. Notify us as soon as possible if you have an infection for which you are being treated.
For the 24 hours before the scan, do not drink coffee, tea, cola drinks and alcohol. You should not exercise heavily for 24 hours before the scan. You can do normal activities such as walking.
You must not eat for at least 4 hours before your scan. This includes avoiding chewing gum, breath mints and candies.
If your appointment is scheduled prior to 10:00 am, from the night before, do not take medicines that contain sugar such as cough syrup. Take your intermediate acting insulin the night before as usual. Intermediate-acting (instead of long-acting) insulin is recommended. Do not take any diabetes medication or insulin the morning of the scan. Have nothing to eat after midnight, and only water to drink. The day of your scan, you may drink plain water only. You may drink water up to the time of your scan. You should be well hydrated. You may take your other non-diabetes medicines if they are safe to take on an empty stomach. Don’t use other medications you need to take with food.
If your appointment is scheduled after 10:00 am, from the night before, do not take medicines that contain sugar such as cough syrup. Take your intermediate / long-acting insulin the night before as usual. You may have an early light breakfast to be finished at least 4 hours before the time of the appointment. It should be a light breakfast with high protein and low carbohydrates e.g., hard-boiled egg or bacon with water, but no toast, no milk, no juice. Then take nothing except plain water until your test is finished.
Take your diabetes pills or rapid acting or short acting insulin around the time of your meal as normal. Take your diabetic pills or rapid acting insulin at least 4 hours before your appointment or take your regular / short acting insulin at least 6 hours before your appointment. Do not use intermediate or long-acting insulin the morning of your scan.
The day of your scan, you may drink plain water only. You may drink water up to the time of your scan. You should be well hydrated. You may take your other non-diabetes medicines if they are safe to take on an empty stomach. Don’t use other medications you need to take with food.
We may ask you to take an X-ray contrast by mouth before your scan. We will give you additional directions on how to take it if this is required.
Please wear warm clothing, even in summer. It is important that you do not get cold in the two hours before we scan you, or the image quality shall be of low quality. Dress in clothes without large metal belts, zippers or buttons if possible. Leave jewelry at home.
