Positron emission tomography (PET), also known as PET imaging or scan, is a type of nuclear medicine imaging that identifies changes at the cellular level, helping to diagnose diseases in their early stages. The test evaluates oxygen use, blood flow, sugar metabolism, and organ function.
It is commonly used to diagnose cancers, gastrointestinal, endocrine, or neurological disorders, heart diseases, and other abnormalities.
PET scans are usually non-invasive and painless, except for the injection of a radiotracer. Small amounts of radioactive material (radiotracer) are injected, swallowed, or inhaled. These tracers accumulate in areas of tumors or inflammation and are detected by a special camera connected to a computer to produce detailed images.
Preparing for a PET Scan
Preparation varies depending on the type of PET scan, but general guidelines apply to all:
- Follow a limited carbohydrate diet for 24 hours before the scan.
- Do not eat or drink anything (except water) for six hours before the test.
- Drink plenty of water until you reach the diagnostic center.
- Contact your insurance provider to confirm coverage and pre-authorization.
- Dress comfortably; you may be asked to change into a hospital gown.
- Leave valuables like jewelry and watches at home.
- Avoid strenuous exercise for 48 hours before the scan.
- Bring music or a device to relax, if approved by your doctor.
- Do not bring metal objects like dentures, eyeglasses, or hearing aids.
- Take your routine medications as instructed.
- Carry copies of previous PET, CT, or MRI scans for comparison.
- Diabetics: Monitor blood sugar closely for 48 hours before the test and take medications as directed, usually at least four hours before the scan.
- Arrive 15–30 minutes early.
- Be ready for identity verification and screening forms.
- Your doctor may order lab tests before contrast is given.
Diet Recommendations
A strict low-carbohydrate diet is required for 24 hours before the scan.
Foods Allowed:
- All meats
- Poultry
- Hard cheeses
- Eggs
- Butter
- Non-starchy vegetables (spinach, broccoli, green beans)
- Oils
- Nuts and unsweetened peanut butter
- Margarine
- Diet soda and zero-calorie drinks
Foods to Avoid:
- Bread, rice, pasta, cereals
- Milk, yogurt
- Jams, jellies, desserts, honey, candy
- Fruits and fruit juices
- Starchy vegetables (corn, peas, potatoes)
- Gravies
- Sugar
- Coffee, tea, caffeinated or decaffeinated drinks
- Alcohol
- Nutritional shakes or smoothies
Information to Provide Before the Exam
Inform your healthcare provider about:
- Current health conditions
- Diabetes (you’ll get special instructions)
- All medications, vitamins, and supplements
- Allergies or adverse reactions to medications
- Pregnancy or breastfeeding
- Claustrophobia or discomfort in small spaces
Note: These guidelines are general. Always follow your doctor’s specific instructions.
What to Expect During a PET Scan?
After check-in and screening, a technologist will explain the procedure, measure your height and weight, and answer questions.
An IV line will be inserted. A small blood sample may be taken to check blood sugar. Then, a glucose solution with a radioactive tracer is injected. The injection is painless, though you may feel a cool sensation in your arm.
You’ll wait 30–90 minutes for the tracer to distribute through your body. You must remain still and relaxed.
You’ll lie on a table that slides into a large, doughnut-shaped scanner. Stay still during imaging; you may be asked to hold your breath. The technologist can hear and speak to you throughout.
In some cases, a catheter may be placed in the bladder, causing temporary discomfort.
After the scan, you can usually resume normal activities. Drink plenty of water to help flush out the radioactive tracer. The radioactivity decays naturally over time and is excreted in urine or stool.