What it Shows and Why It’s Ordered
What it Shows and Why It’s OrderedA positron emission tomography (PET) scan can detect diseased cells in organs and tissues by visualizing how your cells metabolize a medication called a radiotracer. Because diseased cells absorb more of the radiotracer than healthy cells, PET scans can be helpful for staging and monitoring cancer.
- PET scans can determine whether a cancer is localized or if it has spread. If it has spread to other areas, this test can identify the primary tumor source.
- Cancer care teams use PET scans to evaluate how well a tumor is responding to treatment, or whether cancer has returned after treatment.
- A hybrid PET/CT scan can create highly precise 3D images that help visualize anatomy and metabolic function at the same time.
- A PET scan appointment typically takes 2 to 3 hours to allow time for the radiotracer to move through your body. The actual imaging test takes 15 to 45 minutes .
- Full results are usually available within 1 to 2 days, but your radiologist may discuss preliminary results with your oncologist right after the scan.
What it is | Why it’s used in cancer care | When it’s ordered | What to expect | How to prepare | Understanding results | Why choose NewYork-Presbyterian | Scheduling & locations | FAQs
Why are PET scans used in cancer care?
Why are PET scans used?Your care team will recommend a PET scan when they need more information, such as whether a cancer has spread, to guide a treatment decision.
Common reasons PET scans are used
- Diagnosis support. PET scans help clarify whether a suspicious mass or abnormality seen on another scan is likely active cancer, and may help guide where to biopsy.
- Staging. PET scans can determine whether cancer has spread to lymph nodes or distant organs.
- Treatment targets. PET scan can identify target molecules in the tumor for your individualized treatment choice maximizing tumor killing and minimizing side effects.
- Treatment response. PET scans can show whether chemotherapy, radiation, or immunotherapy is working, sometimes before size changes are visible on a CT scan or MRI.
- Recurrence detection. If symptoms return or tumor markers rise, a PET scan helps identify whether cancer has come back, and where.
PET scans are not routine for every cancer type or every patient. Some cancers are better evaluated with a CT scan, MRI, ultrasound, or lab testing. Your oncology team will recommend a PET scan when the results are likely to influence decisions about your care.
What happens after my doctor orders a PET scan?
What happens after my doctor orders a PET scan?Here is a simple overview of what happens once your doctor recommends a PET scan:
- Referral or order
Your doctor places the order for a PET scan, often after reviewing symptoms, lab results, biopsy findings, or other imaging such as CT or MRI. Insurance authorization may be required before scheduling. - Preparation
You’ll receive specific instructions for your scan ahead of time from your doctor or PET Team. Tell your doctor about any vitamins, supplements, or medicines you take, as well as whether you are or might be pregnant or breastfeeding. You may be required to fast before some PET scans. If you take medication for diabetes, talk to your doctor about how to adjust your medication while preparing for the scan. - Tracer injection and uptake period
You will receive a small amount of the radiotracer through an IV. You’ll then rest quietly for about 30 to 60 minutes while the tracer circulates and is absorbed by your tissues. - The scan
You’ll lie still on a padded table that moves slowly through the PET scanner. The scan is painless. The imaging portion typically takes 15 to 45 minutes, and it’s important to stay completely still for clear images. PET scanner has a large opening in the machine and no moving parts. - Image review & results
A radiologist interprets the images and sends a report to your ordering physician. This can take 1 to 2 days. The results will be compared to your previous imaging studies if any are available. - Next visit discussion
Your doctor reviews the results with you and explains what they mean for staging, treatment planning, or follow-up care.
What should I expect on the day of a PET scan?
What should I expect on the day of a PET scan?Before you receive your PET scan, you will receive a dose of the radiotracer, usually through an IV. After, you may need to wait 30 to 60 minutes for the medication to move through your body. During this waiting period, you may need to avoid moving or talking.
During the scan, the doughnut-shaped scanner 3 feet wide will take a series of pictures. You will need to stay completely still during your scan to capture clear images. If you are also having a CT scan, it will be done at the same time as your PET scan.
After the scan, be sure to drink plenty of water to help flush the radiotracer from your body. Unless you’re instructed otherwise, you can immediately resume your normal diet and activities.
How do I prepare for a PET scan?
How do I prepare for a PET scan?Preparing for a PET scan helps ensure the images are as accurate as possible. Your care team will give you specific instructions based on the type of radiotracer used and your personal health history. Always follow the instructions provided by your doctor or imaging center.
You may be asked not to eat or drink (except water) for several hours before the scan. This is especially common for PET scans that use a glucose-based tracer, since food can affect how the tracer is absorbed. Your provider will tell you whether you need to fast, and for how long. Depending on the type of PET scan, you may be asked to avoid smoking or limit caffeine or alcohol beforehand.
Vigorous physical activity before a PET scan can alter how the tracer distributes in your muscles. You may be asked to avoid intense workouts or heavy exertion for a period of time before your appointment.
Tell your doctor about all medications, vitamins, supplements, and herbal products you take, and bring an up-to-date list of your medications and doses to your appointment. Some medication may need to be adjusted before the test.
- If you have diabetes, your medication or insulin dose may need temporary adjustment. Your care team will give you individualized guidance.
- If you are pregnant or might be pregnant, let your doctor know right away.
- If you are breastfeeding, ask whether you’ll need to freeze for 24h breast milk that you produce after the scan, since the radiotracer can get into breast milk.
If you get anxious in tight spaces, tell your doctor ahead of time. In some cases, a mild relaxation medication may be offered. If you receive one, you’ll need someone to drive you home.
What precautions do I need to take after my scan?
What precautions do I need to take after my scan?While you can typically get back to your normal activities right away after a PET scan, it’s important to take steps to prevent exposing others to radiation. Double-flush toilets for 6 to 10 hours after your scan, and avoid close or prolonged contact with pregnant women, infants, and young children for 12 to 24 hours. Contact your doctor if you feel nauseous, dizzy, or develop any skin issues around your IV site after your scan.
Understanding PET scan results
Understanding PET scan resultsAfter your PET scan, a radiologist reviews the images and sends a detailed report to your ordering physician, who will discuss your results with you at a follow-up appointment.
PET scans highlight areas where the radiotracer has accumulated, known as “areas of uptake.” Your care team will explain where they see areas of uptake (for example, a lymph node or specific organ), and what this means for your care.
Importantly, not all uptake means cancer is present. Inflammation, recent surgery, or infection can also cause increased uptake.
You may hear the term “standardized uptake value” (SUV), which is a numerical measure of how much tracer is concentrated in a particular area compared to the rest of your body. Generally, a higher SUV suggests higher metabolic activity. Your doctor will use your SUV alongside the scan images, your medical history, and other test results to make clinical decisions.
Even when a PET scan provides valuable information, it does not always give a final answer. Your care team may recommend follow-up imaging such as a CT scan or MRI to monitor changes over time, a biopsy to confirm whether a suspicious area is cancer, or an additional PET scan after treatment to assess your body’s response.
Why choose NewYork-Presbyterian for oncologic imaging
Why choose NYPAt NewYork-Presbyterian, we fully integrate oncologic imaging into comprehensive cancer care. Radiologists specializing in cancer imaging work closely with medical oncologists, surgical oncologists, and radiation oncologists across our system, and we frequently review complex cancer cases in multidisciplinary tumor boards to align imaging interpretation with real-time clinical decision making.
The recently renovated, state-of-the-art PET/CT Center at Columbia/NewYork-Presbyterian Advanced Imaging provides outpatient PET and CT scans to the Columbia University Irving Medical Center community and beyond.
Advanced imaging techniques, including PET and hybrid PET/CT or PET/MRI, support our precision medicine by helping teams more accurately stage cancers, select individualized treatment, monitor response to targeted therapies or immunotherapy, and guide biopsies to the most biologically active areas.
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