Free Guide to Preparing for Your PET Scan

What Is a PET Scan and How Does It Work

A PET scan stands for Positron Emission Tomography scan. It's a medical imaging test that doctors use to look at how your body's organs and tissues are working. Unlike X-rays or CT scans that show the structure of your body, a PET scan shows the function—meaning how active different parts of your body are at the cellular level.

During a PET scan, you receive an injection of a radioactive substance called a tracer. This tracer contains a small amount of radioactive material combined with a sugar or glucose substance. The radioactive part is minimal and designed to be safe for diagnostic purposes. Your body absorbs this tracer, and it collects in areas where cells are using more energy. Cancer cells, for example, typically use more glucose than normal cells, so they show up brighter on the scan.

The PET scanner is a large, donut-shaped machine. You lie on a table that slides into the center of the machine. The scanner detects the radiation from the tracer and creates detailed pictures of your body. The entire scan process usually takes 30 to 60 minutes, though the actual scanning time is often shorter. The images are displayed on a computer screen, and a radiologist analyzes them to help your doctor understand what's happening inside your body.

PET scans are used to detect and monitor several types of cancer, including lung cancer, breast cancer, colorectal cancer, and lymphoma. They're also used for brain imaging to evaluate conditions like Alzheimer's disease, Parkinson's disease, and epilepsy. Cardiologists may order PET scans to assess blood flow to the heart and determine if someone has had a heart attack.

The radiation dose from a PET scan is relatively low. According to the American College of Radiology, the effective radiation dose from a PET scan is comparable to the background radiation you're naturally exposed to over the course of a year. The radioactive tracer typically leaves your body within a few hours, mostly through your urine.

Practical Takeaway: Understanding that a PET scan is a functional imaging test—not a structural one—helps you know why your doctor ordered it. It shows activity levels in your organs and tissues, which is different information than what X-rays or ultrasounds provide. Write down any questions about why your specific scan was ordered, as this context will be useful during your preparation.

Pre-Scan Preparation: What Your Doctor Will Tell You

Before your PET scan, your doctor's office will send you preparation instructions. These instructions are important because they help ensure your scan produces clear, accurate images. The preparation process typically begins 24 hours before your appointment, though some instructions may start a few days earlier.

One of the most critical preparation steps involves your diet. Most people preparing for a PET scan need to stop eating solid food about 4 to 6 hours before their appointment. This fasting period is necessary because food in your digestive system can interfere with the scan images. During this fasting window, you typically can drink water and sometimes other clear liquids, but your doctor's office will specify which liquids are allowed. Some facilities permit unsweetened tea, black coffee, or broth, while others want only water. Always follow the specific instructions from your imaging center.

Blood sugar levels also matter significantly for PET scans. If your blood sugar is too high before the scan, it can affect the image quality. This is especially important if you have diabetes. Your doctor may ask you to check your blood sugar before arriving and may give you specific target ranges. Some people with diabetes may need to adjust their insulin dose on the day of the scan, so discuss this with both your doctor and your diabetes care team.

You'll also need to arrange transportation to and from your appointment. While some people can drive themselves after a PET scan, it's often safer to have someone else drive you, especially if you received sedation or if the scan took longer than expected. Ask your doctor's office whether you should arrange a ride.

Medications present another consideration. In most cases, you can take your regular medications as usual on the day of your scan. However, if you take diabetes medication, heart medication, or certain other drugs, inform your doctor's office because they may adjust the timing. Never stop taking prescribed medications without explicit instructions from your doctor.

Wear comfortable, loose-fitting clothing to your appointment. You may need to remove some clothing during the scan, so avoid clothing with zippers, metal buttons, or snaps when possible. Metal objects can interfere with the imaging, so leave jewelry, watches, and other metal accessories at home.

Practical Takeaway: Create a checklist based on the specific instructions your doctor's office provides. Check off each item as you complete it in the days before your scan. Keep the phone number for your imaging center handy in case you have questions about any preparation step.

What to Expect on the Day of Your Scan

Arrival at the imaging center typically happens 15 to 30 minutes before your scheduled appointment time. During check-in, you'll provide insurance information and sign consent forms. The staff will review your preparation—asking whether you fasted as instructed and whether you took any medications. Tell them about all medications you're taking, including over-the-counter drugs and supplements, as some can affect scan results.

A technologist will take you to a preparation room where you'll change into a hospital gown if needed. They'll check your vital signs, including blood pressure, heart rate, and temperature. If you have diabetes, they may check your blood sugar at this point. The technologist will also ask about any allergies, especially to iodine or contrast dyes, since these could indicate sensitivity to the radioactive tracer.

Next comes the tracer injection. A nurse or technologist will insert an IV line, usually in your arm, and inject the radioactive tracer. You won't feel pain during the injection, though you may feel slight pressure. After the injection, you'll wait in a quiet room for about 45 to 60 minutes. During this waiting period, the tracer spreads through your body and accumulates in the areas your doctor wants to image. Many imaging centers have comfortable waiting areas with chairs or recliners. Some facilities allow you to bring a book or headphones to use during this waiting time.

When it's time for the actual scan, a technologist will escort you to the PET scanner room. The scanner is a large, cylindrical machine with a bed that slides in and out. You'll lie on the bed, and the technologist may position pillows or cushions to keep you comfortable and still. It's important to remain as motionless as possible during the scan, as any movement can blur the images. The technologist will explain the scan process and answer any last-minute questions before leaving the room. They'll still be able to see and hear you through a window and speaker system.

The scan itself is quiet, though you may hear some humming or clicking sounds as the scanner operates. The bed will move slowly through the scanner opening. The entire scan process usually takes 30 to 45 minutes. You may be asked to hold your breath for short periods during certain parts of the scan. The technologist will tell you through the speaker system when to breathe normally and when to hold your breath.

After the scan completes, the bed slides back out, and you're free to get up. You can usually return to normal activities right away. Many people feel completely fine after a PET scan with no side effects.

Practical Takeaway: Plan to spend 2 to 3 hours at the imaging center total, accounting for check-in, the waiting period, and the actual scan. Bring your insurance card and any identification documents. Wear comfortable shoes since you'll be walking to different areas of the facility.

Managing Anxiety and Physical Comfort During Your Scan

Some people feel anxious about medical imaging, particularly if they're concerned about confined spaces or if they're worried about their scan results. Understanding what to expect can reduce anxiety significantly. The PET scanner opening is fairly wide compared to some other medical machines, and you're not enclosed completely—you can see out, and staff can see you throughout the process.

If you have claustrophobia or significant anxiety about enclosed spaces, mention this to your doctor's office when you schedule your appointment. Many imaging centers can offer strategies to help you feel more comfortable. Some facilities allow you to keep your eyes open during the scan and focus on a fixed point. Others permit you to listen to music through head