One of the most advanced imaging test available to patients and radiologists is often considered to be a PET/CT scan, the combination of two different imaging technologies: positron emission tomography (PET) and computed tomography (CT). When the PET and CT scans are performed on the same machine at the same time, radiologists are able to obtain a more detailed image than either test would provide by itself.
PET is a type of nuclear medicine exam that measures the metabolic activity of the cells in body tissues, helping to visualize the biochemical changes taking place in the body. Meanwhile, CT acquires images at a variety of angles of a patient’s body, capturing organs, tissues, and bones in cross-sectional ‘slices.'
In a PET/CT scan, the PET and CT images are fused (or co-registered) together, precisely aligning the biochemical or metabolic activity seen on the PET images with the corresponding CT anatomical imaging. This technological capability provides an enhanced level of detail to radiologists, pinpointing abnormal metabolic activity and thereby enabling a more exact diagnosis.
Why is PET/CT ordered?
The use of PET/CT scanning is integral to modern healthcare. This highly specialized procedure, with an estimated two million scans performed annually, has primarily found its applications in diagnosing and monitoring cancer and brain disorders since its clinical introduction in the early 2000s.
Thanks to its multidimensional imaging capabilities, PET/CT provides precise localization of precancerous, cancerous, and certain types of diseased cells in various body parts including the skin, lungs, head and neck, breasts, ovaries, lymph nodes, testicles, thyroid, pancreas, and esophagus—even at early stages of disease.
Additionally, PET/CT scanning plays a crucial role in locating seizure activity in patients, evaluating stroke damage, and distinguishing Alzheimer's from other dementias and brain diseases. It's also used in assessing heart blood flow, identifying bone lesions, and differentiating between scars and cancers.
In the context of cancer treatment, PET/CT is instrumental in determining the stage of the disease and monitoring the effectiveness of treatments such as chemotherapy and radiation therapy.
What is injected?
As it is a nuclear medicine procedure, PET scans require the intravenous injection of a radiotracer, which is a type of radiopharmaceutical. The intravenous injection may be performed up to 90 minutes prior to the scan. Commonly used radiotracers include prostate-specific membrane antigen (PSMA), Sodium Fluoride (NaF), and brain imaging tracers like Amyvid (Florbetapir), Neuraceq (Florbetaben), and Vizamyl (Flutemetamol). These radiopharmaceuticals play a crucial role in disease diagnosis and therapy.
Preparing for a PET/CT exam
Discuss with your doctor
Before ordering a PET/CT scan, your doctor will discuss with you any existing allergies or illnesses, and review your current prescription and non-prescription medications, including vitamins and herbal supplements. If you are pregnant or nursing, this is crucial information your doctor will need to know before ordering the exam.
Recommended diet and food restrictions 24 hours before exam
For FDG PET/CT, dietary restrictions are important due to the use of glucose as the radiotracer. To prevent competing sugars from affecting the distribution of the radiopharmaceutical and subsequent image quality, avoid carbohydrate-rich foods, sugar, and caffeine in the 24 hours before the exam. Failure to do so could affect the quality of the scan and might necessitate a rescheduling.
DO NOT EAT LIST:
Carbohydrate-rich foods like bread, cereal, potatoes, rice, noodles, snack chips, or energy bars; canned foods and salad dressings that contain sugar, pickles, ketchup/barbecue sauce, or desserts or candy of any kind.
Drinks like caffeinated coffee or tea, carbonated beverages, hot chocolate, beer, wine, or alcohol.
DO EAT:
Any kind of meat or seafood, eggs, cheese, green vegetables only, and salads dressed with only oil and vinegar.
You should only drink water during this 24-hour period.
Please fast for six hours prior to the exam, consuming only water during this period.
Depending on your existing medical conditions, your doctor may give you different instructions for preparation, especially if you are diabetic.
Having the exam
When you arrive at our imaging center and have checked in, we’ll test your blood sugar and place an intravenous (IV) line in your arm. You’ll receive a radiopharmaceutical injection through the IV 60 minutes before the exam.
We’ll escort you to a special waiting room that is conducive to relaxing with minimal activity and talking. Just before the exam takes place, we’ll request that you remove any metal items from your body—this includes jewelry, hair accessories, and all clothing containing metal, and we will provide you with a locker for these items. We’ll also ask you to use the restroom to empty your bladder and to change into a provided gown before entering the PET/CT suite.
If you are claustrophobic, there is no need for concern. The PET/CT scanner is not as confining as a tubular MRI scanner; rather, it is donut-shaped and closely resembles a CT scanner. We’ll position you on your back on the scanner table in a comfortable position with a headrest.
If your doctor has prescribed medications for claustrophobia, please bring them with you and take them 45 minutes before the exam. Additionally, please arrange for someone to take you home after the exam, as it is not safe for you to drive.
The CT scan is performed first, followed by the PET scan. You’ll be required to lie still as the table you are on slowly moves through the scanner. The entire scanning process is non-invasive and painless; you won’t feel a thing.
The entire exam process takes about 20 minutes, thanks to Radiology Associates’ time-of-flight (TOF) PET/CT scanners. Our state-of-the-art scanners enhance the speed and productivity of the scan, aiming to make the exam process as comfortable as possible for patients.
TOF PET/CT scanners also acquire high-resolution imaging for all body types, including large-bodied patients, and help in enhancing image quality by reducing noise and increasing sensitivity.
After the exam
You will be asked to drink at least five glasses of water to help flush the radiotracer out of your body. The radioactive tracer emits very low radiation and will naturally diminish from your body within hours.
Your doctor will review your scans and interpret the results. They will discuss findings with you within a few days. We recommend following up with your doctor for any further questions and discussions.
Note
Safety is our utmost priority at Radiology Associates. We adhere to the highest safety standards and use state-of-the-art equipment. Our staff comprises experienced professionals who provide the highest level of care and patient-centered service.
References:
1. Radiological Society of North America (RSNA). "PET/CT". RadiologyInfo.org. Available at: https://www.radiologyinfo.org/en/info/pet (Accessed 7/4/2023.)
2. Schaart DR. "Physics and technology of time-of-flight PET detectors." Phys.Med.Biol. 2021 Apr 21;66(9). doi: 10.1088/1361-6560/abee56
3. Statistica. (2021, November). Health, Pharma & Medtech: Medical Technology section. Rate of PET examinations in the United States from 2004 to 2020 (per 1,000 population). Available at: https://www.statista.com/statistics/962337/pet-examinations-in-united-states-rate-per-one-thousand. (Accessed 7/4/2023.)
4. Suri S. "Update on time-of-flight PET imaging." J Nucl Med. 2015. 56(1):98-105. doi.org/10.2967/jnumed.114.145029.
