How to Prepare for a PET Scan?

by Dr Amit Jotwani


Positron emission tomography (PET), also known as PET imaging or scan, is a type of nuclear medicine imaging, which identifies changes at the cellular level, thus helping to diagnose a disease even in the early stages. The test evaluates oxygen use, blood flow, sugar metabolism, and the functioning of the tissues or organs. This test can help diagnose various conditions including cancers, gastrointestinal, endocrine or neurological disorders, heart diseases and other abnormalities.

PET scan is usually non-invasive and painless, except when you receive injections. It uses small amounts of radioactive materials called radiotracers or radiopharmaceuticals, which accumulate in the regions of tumours or inflammation or bind to specific proteins. Based on the type of exam, the radiotracer is either injected, swallowed or inhaled as a gas. The radiotracers emit radioactive emissions, which are detected by a special camera or device, which is connected to a computer that produces images of the organ or tissue.

Preparing for a PET Scan

Preparation for a PET scan will vary according to the type of scan being performed. Hence, you must prepare correctly for the imaging test. However, the following are some instructions given for all types of PET scan:

  •   Follow a limited carbohydrate diet for 24 hours before the scan.
  •   Do not eat or drink anything six hours before the test, except water.
  •   Drink as much water as you can until you reach the diagnostic centre or the hospital.
  •   Contact your insurance company to know if it will pay for the scan. Find out if any approval or pre-authorization is required.
  •   Dress comfortably for the scan. However, you will be asked to change into a hospital gown.
  •   Do not carry any valuables like jewellery or a watch, leave them at home.
  •   Do not perform any strenuous exercises or activities 48 hours before your test.
  •   Prepare your music and device to help you relax during the test, only if approved by your doctor.
  •   Do not take anything that contains metal to your test, such as dentures, eyeglasses, or hearing aids.
  •   Take routine medications as instructed.
  •   Carry the copies of previous PET CT scans,  any recent CT scans or MRI’s done for comparison.
  •   If diabetic, monitor and control your blood sugar levels carefully 48 hours before the test.
  •   Take your diabetes medication at least four hours before the exam as instructed.
  •   Reach the centre or hospital 15-30 minutes before your scan.
  •   Your identity and the exam scheduled will be verified by a technologist.
  •   You may be asked to complete a screening form.
  •   Your doctor may order some lab tests before the contrast is given.

Diet recommendations

For the PET scan, one must follow a strict low carbohydrate diet for 24 hours before the test. Here are some of the foods to be avoided and those that are allowed.

The following foods are allowed:

  •   All meats
  •   Poultry
  •   Hard cheeses
  •   Eggs
  •   Butter
  •   Non-starchy vegetables like spinach, broccoli, green beans
  •   Oil
  •   Nuts and unsweetened peanut butter
  •   Margarine
  •   Diet soda and zero-calorie drinks

The following foods should be avoided:

  •   Bread
  •   Rice
  •   Milk
  •   Yoghurt
  •   Jams and jellies
  •   Cereals
  •   Pasta
  •   Dry beans
  •   Nutritional shakes or smoothies
  •   Fruits and fruit juices
  •   Starchy vegetables like corn, peas, potatoes
  •   Gravies
  •   Sugar, desserts, honey or candy
  •   Coffee or tea
  •   Caffeinated or decaffeinated drinks
  •   Alcohol

Information that must be provided by the patient before the exam

Before scheduling your PET-CT scan, you must inform your healthcare provider about your health condition and other concerns that may affect the PET scan procedure and the results. Thus, inform the doctor regarding the following aspects:

  •   Inform the healthcare team of the current health conditions that you have been diagnosed.
  •   Notify if you are diabetic; you will receive special dietary recommendations and instructions for your medications.
  •   Tell what medications you are taking currently, including vitamins and other supplements.
  •   Inform if you have any allergies or adverse reactions to medications.
  •   Notify if you are pregnant or breastfeeding.
  •   Tell if you are claustrophobic and don’t like to be in small spaces.

Note: These instructions and guidelines are for any type of PET scan. These may vary based on the type of PET scan recommended for your condition. Contact your doctor for specific instructions.

What to expect during a PET scan?

After completing the screening form and identity verification, the technologist will take you to the procedure room. The technologist will explain what will happen during the scan, measure your height and weight, and address your queries.

A small intravenous needle will be inserted in one of your veins. A small amount of blood may be withdrawn to test the blood sugar levels. Then, the glucose solution with a radioactive tracer will be injected through the IV line; the injection is painless and free from any side effects. After the injection of the tracer, you may feel a cold sensation moving up your arm. This tracer takes about 30 to 90 minutes to travel throughout the body, while you remain still and stay relaxed.

You may be asked to lie on your back on the examination table; your position may vary based on the region where the doctor wants the scan. The PET scan device is a large, doughnut-shaped machine with a table in between. After you lie on the table, it slides quickly through the hole. The table can be slid back and forth, raised or lowered, or tilted to the sides, allowing the technologist to get pictures from different angles.  You must remain still during the test; the technologist may ask you to hold your breath to prevent blurring of the images. You will be able to talk to the technologist during the scan. The scanner will detect the radioactive tracer and record its distribution in the body.

For some procedures, a catheter may be inserted into your bladder, which causes temporary discomfort.

After the test, you may resume your normal activities, unless instructed otherwise. Special instructions will be briefed by the technologist, nurse or doctor. The injected radioactive tracer will lose its radioactivity over time through the process of radioactive decay. In the following hours or days, the tracer may also pass out through urine or stool; drinking plenty of water can help flush the radioactive tracer out of the body.


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