Getting a PET scan starts with a doctor’s order. You cannot schedule one on your own. A physician, typically an oncologist, cardiologist, or neurologist, must determine that a PET scan is medically necessary and submit a referral to an imaging center. From there, the process involves insurance authorization, preparation at home, and the scan itself, which takes about two hours total at the facility.
Why Doctors Order PET Scans
PET scans detect how your cells are using energy, which makes them especially useful for finding cancer, evaluating heart damage, and assessing brain disorders like epilepsy and dementia. Diseased cells absorb the radioactive tracer differently than healthy ones, creating visible “hot spots” on the image. Most PET scans today are combined with a CT scan (called PET-CT), which layers metabolic activity on top of detailed anatomical images.
The most common reason for a PET scan is cancer. It’s used for diagnosis, staging (determining how far cancer has spread), restaging after treatment, and checking for recurrence. Specific cancers with well-established PET scan indications include lung cancer, lymphoma, melanoma, colorectal cancer, esophageal cancer, head and neck cancers, and breast cancer. For breast cancer specifically, PET is typically used alongside standard imaging when doctors suspect the cancer has spread to distant sites or need to monitor how a tumor responds to treatment.
Outside of cancer, PET scans evaluate whether damaged heart muscle is still viable before a procedure to restore blood flow. They’re also covered for pre-surgical planning in patients with seizures that don’t respond to medication.
Getting Insurance Approval
Most insurance plans, including Medicare, require prior authorization before they’ll cover a PET scan. Your doctor’s office handles this, but understanding the criteria can help you anticipate delays. Insurance generally covers PET scans only when the results would change how your condition is managed. For cancer diagnosis, coverage typically applies when the scan could help avoid an invasive biopsy or guide where a biopsy should be performed. For staging, insurers want to see that standard imaging (CT, MRI, or ultrasound) has already been done and the results are inconclusive, or that the PET scan would replace multiple conventional scans.
If your authorization is denied, your doctor can file an appeal with additional documentation explaining why the scan is necessary. This process can add days or weeks, so ask your doctor’s office to submit the authorization request as early as possible. Private insurers often follow Medicare’s coverage criteria closely, but each plan varies, so calling your insurance company directly to ask about PET scan coverage is a practical first step.
How to Prepare Before the Scan
Preparation starts at least 24 hours before your appointment. Most facilities will give you a specific instruction sheet, but the core rules are consistent everywhere.
- Fasting: You’ll need to avoid eating for at least 6 hours before the scan. The tracer used in most PET scans is a radioactive form of sugar, and any food in your system (especially carbohydrates) can interfere with how your cells absorb it.
- Diet restrictions: If you eat a meal before your fasting window, stick to protein like eggs, chicken, fish, or meat. Avoid bread, rice, pasta, potatoes, and anything sweet. Even gum, candy, flavored water, and artificial sweeteners can affect the results and force a repeat scan.
- Water: Drink at least half a quart of plain water starting at least an hour before your exam. Water helps flush the tracer through your system and improves image quality. No flavored water.
- Exercise: Avoid strenuous physical activity for 24 hours before the scan. Muscles that have been working hard absorb more of the tracer, which can create misleading hot spots.
If you have diabetes, your facility will likely schedule you after 11 a.m. You can take your morning diabetes medication with food 6 hours before the exam, but that meal should be high protein and low carb. Your blood sugar needs to be below 160 on the day of the scan. If it’s higher, the scan may be rescheduled.
What Happens During the Scan
Plan to be at the imaging center for roughly two hours, though the actual scanning portion is a fraction of that. When you arrive, a technologist will check your blood sugar with a finger stick and place an IV line, usually in your arm. The radioactive tracer is then injected through the IV. It feels like any other injection; the tracer itself has no side effects you’ll notice.
After the injection, you’ll sit quietly in a dimly lit room for about 60 minutes while the tracer circulates and gets absorbed by your tissues. During this waiting period, you need to stay as still and relaxed as possible. Talking, reading on your phone, or even chewing gum can cause the tracer to concentrate in muscles you’re using, which muddies the images. Most facilities provide a recliner or bed in a private room.
When it’s time for the scan, you’ll lie on a narrow table that slides slowly through a large, ring-shaped machine. The scanner itself is open on both ends and quieter than an MRI, so claustrophobia is less of an issue. The scanning portion takes 15 to 45 minutes depending on the area being imaged. You’ll need to lie still, and the technologist may ask you to hold your breath briefly for certain sections. The machine doesn’t touch you, and the process is painless.
After the Scan
You can eat and drink normally as soon as the scan is over. The tracer is radioactive, but the amount is small and it breaks down quickly. The most commonly used tracer has a half-life of about 110 minutes, meaning half the radioactivity is gone roughly every two hours. Drinking extra water and urinating frequently after the scan helps clear it faster, reducing your radiation exposure by an additional 22% to 25%.
For the rest of the day after your scan, you should avoid prolonged close contact with pregnant women and young children. This is a precaution because children and developing fetuses are more sensitive to radiation. Your facility will give you specific guidance on how long to maintain distance.
If you’re breastfeeding, you may need to pump and discard milk for several hours after the scan. Let your imaging team know ahead of time so you can plan accordingly, such as expressing milk beforehand for your baby to use.
Getting Your Results
A radiologist or nuclear medicine specialist reviews the images and sends a report to the doctor who ordered the scan. In most cases, the report is complete within 24 hours. Your referring doctor will then discuss the findings with you, usually at a follow-up appointment or phone call. Some patient portals release radiology reports directly to you, but the images require expert interpretation, so it’s worth waiting to review them with your doctor rather than trying to read the report yourself.
PET scan results are typically described in terms of tracer uptake. Areas with unusually high uptake suggest increased metabolic activity, which can indicate cancer, infection, or inflammation. Areas with low uptake may suggest dead tissue or poor blood flow. Your doctor interprets these patterns in the context of your symptoms, other test results, and medical history to determine next steps.