Preparing for a PET scan or MRI can seem daunting, but understanding each step helps you feel more confident and calm. These advanced imaging tests provide crucial insight into your health by showing not only the structure of your tissues but also how well they’re functioning. This guide will walk you through what to expect, how to prepare, and how to communicate with your healthcare team to make sure your tests go smoothly and deliver the most accurate results for your care.
What Are PET Scans and MRIs, and Why Are They Important?
If your doctor recommends a PET scan or MRI, it’s because they want a detailed view of what’s happening inside your body. A PET scan (Positron Emission Tomography) involves injecting a small, safe amount of a radioactive tracer, usually a sugar-based substance called FDG. This tracer collects in areas where cells are very active—like cancer cells—making those spots light up on the scan. This helps your doctor see if cancer has spread or how active it is. You can learn more about how PET scans work on the National Cancer Institute website.
MRIs (Magnetic Resonance Imaging) are different. They use strong magnets and radio waves to create clear pictures of your soft tissues—like your brain, muscles, and organs—without using any radiation. MRI helps your doctor see the exact size and shape of any tumors or abnormalities. Together, PET and MRI provide a complete picture: PET reveals how tissues are functioning, while MRI shows detailed anatomy. For a thorough explanation of MRI, check the Mayo Clinic’s MRI overview.
How Should You Prepare for Your PET Scan?
When you’re scheduled for a PET scan, you’ll usually need to fast—meaning no food or drinks except water—for at least six hours beforehand. This fasting helps keep your blood sugar levels steady, so the tracer can clearly highlight problem areas. Avoid caffeine, sugary treats, or carb-heavy meals before your scan because these can affect the results.
Before the scan starts, the healthcare team will inject the tracer through your vein and then ask you to rest quietly for about an hour. This wait gives the tracer time to spread through your body. If you have diabetes or other health conditions, telling your doctor ahead of time is very important. They will guide you on how to manage your medications and blood sugar to get the best possible images.
What to Expect When Getting Your MRI
MRIs are safe and painless, and they don’t involve radiation. However, the machine is a large tube that can feel confining, especially if you feel anxious or claustrophobic. If that’s the case for you, let your healthcare provider know. They can offer strategies—like relaxation exercises or medications—to help you stay comfortable.
Before your MRI, the technologist will check that you don’t have any implants such as pacemakers, cochlear implants, or metal pieces that could be affected by the strong magnetic field. Be sure to remove all jewelry, watches, hairpins, and clothes with metal fasteners to avoid interference.
During the scan, you’ll lie on a table that slides into the tube-shaped machine. It can be noisy, making tapping or knocking sounds, but you’ll be given earplugs or headphones for comfort. Staying as still as possible is key to getting clear images, so the staff will assist to make you as comfortable as possible during the 30 to 60 minutes the scan lasts.
How You Can Help Your Healthcare Team Help You
You know your body best, so sharing your complete medical history and all the medications or supplements you take is really important. Some medicines might need to be paused before your scan. Also, if you have kidney problems or allergies—especially to contrast dyes sometimes used during imaging—be sure to tell your healthcare team so they can take extra precautions.
If you ever feel nervous or claustrophobic about your scan, speak up. Your doctors and technicians want this to be as comfortable as possible for you and can make adjustments or offer support based on your needs.
What Happens During Your PET Scan and MRI?
Your PET Scan Procedure
After the tracer injection, you’ll rest quietly for about an hour while it spreads through your body. Then, you’ll lie still on the PET scanner table while the machine takes pictures—this usually takes 30 to 60 minutes. The scan does not hurt but staying still is important to get clear images.
Your MRI Procedure
During the MRI, you’ll lie on a table that moves inside the tube-like machine. The length of the scan depends on the part of your body being examined, typically between 30 minutes and over an hour. You’ll hear tapping or knocking sounds—ear protection will be provided—and you can communicate with the staff at any time. Staying as still as possible gives the clearest pictures.
Both scans are safe and painless. While it can sometimes be challenging to remain still, knowing what to expect ahead of time helps ease that difficulty.
Frequently Asked Questions
Can I eat or drink before my PET scan or MRI?
For a PET scan, you usually need to fast for at least six hours without food or drinks—except water—and avoid caffeine and high-carb foods. For an MRI, most people can eat and drink as usual unless your doctor tells you otherwise. Always follow your healthcare provider’s instructions carefully.
Is it safe to have an MRI if I have implants or metal in my body?
Not all implants are safe with MRI machines. It’s important to tell your healthcare team about any implants or metal inside your body so they can decide whether MRI is safe for you or if another imaging test would be better.
How long do PET and MRI scans usually take?
A PET scan can take from 30 minutes up to 2 hours, including the wait time after tracer injection. MRI scans typically last between 30 minutes and 1 hour, depending on the area scanned.
What clothing should I wear for my scan?
Wear comfortable, loose-fitting clothes without metal fasteners. You may be asked to change into a hospital gown to avoid any metal interfering with the scan.
What if I feel anxious or claustrophobic during my MRI?
If you worry about feeling anxious or claustrophobic, talk with your healthcare provider beforehand. They can offer solutions such as relaxation techniques, open MRI options, or medication to help you stay calm and comfortable.
For more in-depth guidance on PET scans, visit Cancer Research UK’s PET scan information page. Being well-prepared and informed is one of the best ways to ensure your scans provide the clearest information possible for your care.
