Preparation For Your PET/CT Scan

Why would my doctor refer me to have this procedure?

The reasons for having a PET-CT scan are continually evolving, with new ways of testing a broader range of conditions and symptoms, and using new radioactive substances. Nevertheless, most PET scans are carried out in patients with cancer. PET-CT is important for identifying certain cancers and assessing their spread through the body. This will allow your doctor to determine the most appropriate treatment for you and advise you on your options. Scans are also used at intervals to determine whether the cancers have responded to your treatment.

How do I prepare for a PET scan?

You will receive specific instructions based on the type of PET scan you are undergoing. If you are unsure about any aspect of preparation, contact the facility where your PET scan is going to be carried out.

It is important that you let staff at the hospital or radiology facility where you are having the scan done know if you are (or think you could be) pregnant or are breast-feeding.

Women who are breast-feeding and people who are the primary or sole carer for small children may need to make special preparations for after the test, to stop breast-feeding for a short time and to avoid close contact with young children. This is due to the small amount of radioactivity your body may release for a while after the test. Talk to your referring doctor or the nuclear medicine facility where you will have the test for details.

Take with you to your appointment any previous X-ray or radiology images you have, as comparison with these by the nuclear medicine physician (a specialist doctor), who looks at and interprets your PET scan, can be very helpful.

For an FDG PET-CT, you will be asked to not eat anything for several hours before the PET scan, because this may alter your sugar metabolism and may affect the quality of the images or pictures. Drinking water is both acceptable and advised so that you are not dehydrated. If you have diabetes, you will be provided with specific instructions and may need to stop taking some diabetes medications before having the scan.

You need to wear comfortable, loose clothing, and will generally be changed into a hospital gown. It is important that you are not wearing metal, including jewellery, watches, zips and bra hooks, as these can affect the quality of the images produced.

What happens during a PET scan?

After you arrive at the hospital or radiology facility, a nurse or nuclear medicine technologist will explain the procedure and prepare you for the PET scan. You will be asked to change into a gown. A small needle will be inserted into a vein, usually in your arm or the back of your hand, to fit an intravenous line (a thin plastic tube) through which the liquid radioactive material is injected. A brief medical history will be taken to ensure the optimal (or best) scanning method is used and to also help with subsequent image interpretation. Your blood sugar level will be checked, as high or low blood sugar levels can alter the appearance of the scan. The radioactive substance is then injected into your vein through the intravenous line.

If you are having an FDG-PET scan, you will be asked to rest quietly in a bed or arm chair, avoiding movement or talking for 90 minutes. During this time you will be alone. You may be asked to drink some contrast material that moves through your stomach and bowel, and helps to improve the quality of the images. Occasionally, depending on the medical condition or symptom, a catheter (a thin flexible tube) may be placed into your bladder to help improve image quality.

You will then be moved to the scanning room and positioned on the PET scanning bed. It is important to remain as still as possible during the scan, as movement can result in reduced image quality and the images may be blurry. If you are uncomfortable after being positioned on the bed, please tell the nurse or technologist.

If you are having a PET-CT, the CT scan is done first and takes less than 2 minutes. The PET scan takes approximately 15–20 minutes, but the time will vary depending on the areas of your body being scanned.

The intravenous line will be removed before you leave. You should drink plenty of fluids after the test is finished. This will flush the radioactive substance out of the body through the kidneys and into the bladder

Important Infromation


  • As with any radiology exam, call us in advance if you are pregnant or breast feeding.
  • Drink extra fluids the day before your scan and following your scan.
  • Drink extra PLAIN WATER before arriving for the scan.
  • Dress warm and comfortable. The scan room is cool.
  • Medications (except diabetic medicines) can be taken with plain water at any time, if they can be taken on an empty stomach.

Do Not:

  • Eat, drink (except water – DO DRINK WATER), chew gum, or use breath mints (this includes sugar free items) for 4 hours before the test.
  • Caffeine and strenuous physical activity should be avoided for 12 hours prior to the exam.
  • Insulin and diabetic medicine may not be taken within 4 hours prior to the exam.

Other Considerations:

Diabetics are asked to call the Center for specific instructions.

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