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What is a PET/CT scan?

In a PET/CT exam, information from two technologies is combined to create images that pinpoint the location of abnormal activity in the body.

Positron emission tomography (PET) is a type of nuclear medicine procedure that uses small amounts of a radioactive substance, called a radiotracer or radiopharmaceutical, to measure the activity of the cells in an organ or other tissue in order to evaluate how the organ or tissue is functioning. Computed tomography (CT) is a different kind of imaging procedure that uses X-ray radiation and computer technology to produce very detailed images of structures inside the body. The combined, or hybrid, PET/CT scan can help a doctor make more accurate diagnoses than the two scans performed separately.

Combining the PET and CT scans can provide unique information, including details on both the structure and the function of organs. Because PET imaging can show changes occurring at the level of cells in the body, it can help a physician detect the onset of disease before it is evident on other imaging exams.

Why it's done

PET/CT scans are commonly used for diagnosing and staging cancer and in assessing the effectiveness of cancer treatment. These scans are also performed to help a physician assess blood flow to the heart muscle, evaluate the effects of a heart attack and plan treatment for coronary heart disease, and to aid in evaluating brain abnormalities and diagnosing neurological conditions, among other things.

Our approach

When it comes to a PET/CT scan, the radiologists at Northwell Health Imaging are the power behind the exam. Every PET/CT test is performed with state-of-the-art positron emission tomography and computerized tomography technology, and scans are interpreted by a fellowship-trained nuclear medicine radiologist whose diagnostic skills have been honed by specialized training and thousands of hours of experience. If you need additional care, your radiologist will work side by side with the rest of your care team, collaborating closely to answer your questions and help guide your care.

Northwell Health Imaging offers the largest group of fellowship-trained and subspecialized nuclear medicine radiologists on Long Island, as well as access to all the resources and clinical expertise of New York state’s largest health system. Whether you are here for screening, diagnostic or treatment imaging services, each of our practitioners is committed to providing a caring, comfortable environment and a positive, productive experience.

Risk factors

Nuclear medicine procedures can provide information that may be unattainable using other imaging approaches, and do so at relatively low risk. The radiotracer used for nuclear medicine diagnostic exams is typically administered at a low dose and is therefore accompanied by relatively low radiation exposure to the patient, in line with other diagnostic exams. Nuclear medicine diagnostic procedures have been used for more than five decades, and no long-term adverse effects have been identified from the low-dose radiation exposure involved in the exams.

An allergic reaction to the radiotracer is possible but occurs extremely rarely.

A CT scan involves slightly more radiation exposure than a conventional X-ray exam. The dose of radiation required for a CT scan has not been shown to cause damage, and when a CT scan is recommended, it is because the expected benefits outweigh the risks. However, if you are concerned, discuss possible alternative imaging tests with your doctor.

Some CT scans are done with a substance called contrast material, which enhances the visibility of internal structures. You may be given contrast material to swallow, or you may get it through an intravenous (IV) line. Allergic reactions to the contrast material used for CT scans are possible but are very rare. Tell your doctor if you are taking metformin (brand names include Glucophage, Fortamet and Glumetza). Rarely, people on these drugs can experience kidney damage if given contrast material.

If there is a possibility that you might be pregnant, or if you are breastfeeding, let your doctor or nuclear medicine technologist know. Your doctor may recommend a kind of exam that does not involve ionizing radiation, such as ultrasound or MRI.

What to expect

Most nuclear medicine exams are painless, although if the radiotracer is administered intravenously, you may experience slight discomfort as the IV catheter is placed. (Depending on the type of exam, the radiotracer may be injected, inhaled or swallowed.) The tracer may take seconds, hours or days to travel through your body and collect in the area being studied. As a result, some nuclear imaging tests are performed immediately after administration of the tracer, while for others you may have to return for imaging a few hours or even days after you are given the tracer.

Radiotracers are formulated and ordered specifically for each patient and exam, and must be used within a short window of time. It is important to notify the office 48 hours in advance if you have to cancel or reschedule your appointment.

You may also be given contrast material in addition to the radiotracer. Contrast material increases the visibility of organs and blood vessels on the CT scan. Substances used as contrast material are unlikely to cause allergic reactions or discomfort. However, if you are over 60 or have certain health conditions, you will need a blood test beforehand to make sure it is safe for you.

For the scan itself, you will be asked to change into a gown and lie on a cushioned exam table as the gamma camera takes a series of images. The camera may be in close proximity but will not touch you. While the camera is taking pictures, you will need to remain still, as any motion will diminish the quality of the images.

How to prepare

Continue taking any prescribed medication unless directed otherwise. Dress in comfortable clothes without metal fasteners, zippers, buttons or snaps.

Tell your doctor and the technologist performing the exam about any prescription or over-the-counter medications you’re taking, and about any vitamins or herbal supplements. Also let them know if you have any allergies, illnesses or other medical conditions. Tell your doctor if you’re pregnant or might be pregnant, or if you’re breastfeeding.

You may be asked to lie on your back for an extended period of time for the exam. If that could cause discomfort, you may take an over-the-counter pain reliever, such as ibuprofen (Advil, Motrin) or acetaminophen (Tylenol) before the procedure begins.

Important information to help prepare for your PET/CT.


Unless otherwise directed, you may resume your normal routine after the exam is completed. The tracer will remain in your body for a short time and is cleared through natural functions. Drinking plenty of fluids will help flush it through your system more quickly.


Your PET/CT scan will be read/interpreted by a subspecialized radiologist and the results will be promptly shared with your physician. Your doctor will determine if any followup care is needed.

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