What Is a PET Scan?
shironosov/Getty Images
Medically reviewed by Jane Kim, MD
A positron emission testing (PET) scan is a painless medical imaging test that uses a radioactive tracer (compound) to generate images of the body. These images help a healthcare provider determine organ or tissue functioning. A PET scan is often performed with a computed tomography (CT) scan, which is known as a PET/CT scan.
A radiologist will usually interpret your test results and review them with the referring healthcare provider (the provider who ordered your scan). Radiologists are medical doctors who specialize in medical imaging like PET scans and X-rays. Healthcare providers may use PET scans to diagnose medical conditions like cancer, heart disease, or brain disease, or to assess the effectiveness of medical treatments.
Purpose
Healthcare providers most commonly recommend a PET scan to detect cancer, including where cancer has spread and your response to treatment.
A healthcare provider may also recommend a PET scan to assess other conditions, including:
Brain functioning in people with memory or other cognitive concerns
Cardiac structure and function, such as areas with poor blood flow to the heart or a lung mass
Areas of the brain affected by epilepsy, a chronic neurological condition characterized by recurrent seizures
The effectiveness of heart disease treatment
PET scans can detect disease with high accuracy. For example, a PET scan can be up to 93% accurate in diagnosing early signs of Alzheimer's disease. PET scans are also often more accurate than CT scans at detecting cancer.
How Does It Work?
A PET scanner looks very similar to a CT or magnetic resonance imaging (MRI) machine: a large machine with a round hole in the middle, in which you lie during the procedure.
A PET scan involves ingesting a radioactive tracer—also called a radiotracer. This is usually done via intravenous (IV) injection into your vein, but can also be consumed by mouth or by inhaling it. The approach depends on which area of your body your healthcare provider is examining.
A radiotracer is different than contrast materials used in other imaging procedures like X-rays and CT scans. Contrast materials increase the contrast between body structures and fluids in order to provide clearer images. Radioactive compounds are metabolized (broken down) in the body. Areas with high metabolic activity (like a cancerous area) will "take up" or absorb more of the radiotracer.
A special camera detects gamma rays given off by the radiotracer when you're in the PET scanner. This produces images. The process takes about 10-40 minutes.
You will likely have a PET/CT scan. A CT scanner uses a specialized device that rotates around your body and uses X-rays to generate images. Each rotation of the CT machine is a "slice" that recreates a portion of your body. Together, these slices create a three-dimensional image. A PET scan might also be combined with an MRI, but this is much less common. An MRI uses radio waves and magnets to scan inside the body. Combining two imaging approaches allows the radiologist to connect multiple views of your body and get a more complete picture of the areas examined.
Before the Test
You will be asked to fill out a questionnaire before the PET scan that includes questions like:
Medical conditions
Medications and supplements you're taking
If you are or could be pregnant
If you have concerns about claustrophobia
You will also be asked to remove any metal jewelry or other accessories, as well as hearing aids, as they can interfere with imaging.
A healthcare provider will give you the radiotracer. You might feel a cold sensation moving up your arm if you receive an injection, but you likely won't experience any discomfort. After administering the radiotracer, the provider will ask you to wait for about 30-60 minutes as the compound travels through your body. You'll need to rest and avoid moving or talking during this time.
The PET scan itself is painless, and you will probably not require sedation or anesthesia. If you have claustrophobia or severe anxiety, you can talk to your doctor about taking a relaxing medication before the scan.
The procedure duration depends on which part of your body is being scanned. Most scans take about 30 minutes, including setup time. It may take longer—up to three hours—if the test requires multiple radiotracers or images of several areas of your body.
During the Test
During the PET scan, you will lie on the scanner table. The table will move into and out of the scanner to obtain images. You may hear whirring or moving sounds, but they are not usually excessively loud.
The radiology technician will usually provide you with a device you can use to communicate during the scan, such as a button to push or a speaker that allows you to communicate with the technician. They might remind you to stay still or help you relax if you feel anxious.
Images taken by the PET scan are sent to a computer for your healthcare provider to review. The radiologist or radiology technician will assess the images frequently to ensure they are high-quality. If a scan does not obtain adequate images, the technician may re-scan that area of your body. Performing additional scans of the same area does not mean the technician saw something abnormal.
After the Test
A PET scan is usually performed on an outpatient basis, meaning you can return home after you complete the test. Your body will eliminate the radiotracer within two to 10 hours, but staying hydrated will help flush it out of your system.
You can usually drive yourself home and resume all usual activities after a PET scan. The radiologist or radiology technician will provide additional instructions if needed.
Risks and Precautions
PET scans involve some radiation exposure, and CT scans expose you to more radiation. It's important to discuss potential risks with your healthcare provider before the scan. For example, if you're pregnant, radiation can harm the fetus. The tracer can also contaminate breastmilk, which is why you might want to pump beforehand so you have a supply for the length of time it takes to leave your system.
In rare instances, you may experience an allergic reaction to the radiotracer. Symptoms of an allergic reaction can range from rashes and itchiness to hives, difficulty breathing, and low blood pressure.
Related: Allergies: Signs and Symptoms
PET Scan Prep
A PET scan is usually performed at an outpatient imaging center or hospital. You'll want to wear loose, comfortable clothing that you can easily change out of if needed. You may need to change into a gown for the procedure. You'll also want to avoid wearing any metal jewelry or other accessories.
The healthcare provider that ordered your scan will give you specific instructions. You will need to follow these instructions leading up to the day of the PET scan, based on factors that might interfere with the imaging process.
Instructions might include:
Eat a low-carbohydrate and low-sugar diet 24 hours before the test
Avoid caffeine, alcohol, and tobacco 24 hours before the test
Avoid strenuous exercise before the test
Don't eat or drink anything six hours before the test
You will receive specific instructions if you have diabetes. For example, you might change the timing of an insulin dose. If you're breastfeeding, your healthcare provider may recommend pumping before the scan and discarding breast milk for up to 12 hours afterward.
Results
You can ask your radiology technician at the PET scan how and when you may expect to see your results. Imaging tests like PET scans, MRIs, and CT scans are usually available a few days after the test. However, a more urgent or emergency situation might require more immediate results.
Your healthcare provider may make an in-person follow-up appointment, call you with results, or post your results to a secure patient web portal.
Interpreting Your Results
The radiologist will interpret the results of the PET scan, as well as any other imaging scans, and send them to the referring healthcare provider. Increased activity of cells and the radiotracer (a "hot spot") indicates the potential presence of disease. Decreased activity (a "cold spot") might indicate a tumor. Results can help diagnose a condition or provide additional information on how to move forward with assessment or treatment.
Your healthcare provider will likely recommend additional testing—like a blood or urine test—or a biopsy (tissue sample) if the scan shows abnormalities or areas of possible concern, or if the results were unclear. You may not require any additional testing if everything looks normal.
A Quick Review
A PET scan is a painless imaging test commonly used to assess and diagnose conditions like cancer, heart disease, and brain disease. It's often combined with an additional imaging test, like a CT scan or MRI. Most scans can take about 30 minutes, plus about 60 minutes of preparation time. You'll likely be able to resume your normal activities afterward.
If your healthcare provider recommends a PET scan, ask them about how you can prepare, the testing procedure, and when you can expect results.
For more Health news, make sure to sign up for our newsletter!
Read the original article on Health.
