Positron emission tomography
Positron emission tomography (PET) scans are advanced imaging tests that provide detailed insights into the metabolic activity occurring within your body’s tissues and organs. During a PET scan, you will lie on a comfortable table that gently slides into a doughnut-shaped scanner. This scanner works to produce comprehensive images of your body’s functions, typically taking around 30 minutes to complete.
A positron emission tomography (PET) scan is a type of imaging test that helps doctors understand how your body is working at a cellular level. It’s particularly useful for revealing the metabolic or biochemical function of your tissues and organs. Unlike other imaging tests that primarily show the structure of your body, a PET scan uses a special radioactive drug, called a tracer, to highlight both normal and abnormal activity. This tracer allows the PET scan to often detect diseases by identifying unusual metabolic changes, sometimes even before these conditions are visible on other imaging tests like computerized tomography (CT) or magnetic resonance imaging (MRI).
The tracer, which is key to how a PET scan works, is usually injected into a vein in your arm or hand. It then travels through your bloodstream and accumulates in areas of your body with higher levels of metabolic or biochemical activity. These areas of increased activity often indicate the location of disease. To get a more complete picture, PET images are frequently combined with CT or MRI scans, resulting in what are known as PET-CT or PET-MRI scans. These combined scans provide both functional and anatomical information, enhancing diagnostic accuracy.
Why are PET Scans Performed?
PET scans are valuable diagnostic tools used to detect and monitor a wide range of health conditions, including cancer, heart disease, and various brain disorders. Healthcare providers rely on the information from PET scans to diagnose conditions, monitor the effectiveness of treatments, and guide patient care.
Cancer Detection and Monitoring
PET plus CT
Combining a PET scan with a CT or MRI scan significantly improves image interpretation. The image on the left shows a CT scan, the center image is a PET scan, and the right image is the merged PET-CT scan. Notably, the bright spot in the chest, most clearly seen in the PET and PET-CT scans, indicates lung cancer.
Cancer cells are characterized by their rapid growth and high metabolic rate, which causes them to appear as bright spots on PET scans. This heightened metabolic activity makes PET scans particularly useful in various aspects of cancer management:
- Cancer Detection: PET scans can help identify cancerous tumors in the body.
- Staging Cancer: They are crucial for determining if cancer has spread from its original site to other parts of the body, a process known as metastasis.
- Treatment Monitoring: PET scans can assess whether cancer treatment, such as chemotherapy or radiation therapy, is effectively reducing metabolic activity in tumors, indicating treatment success.
- Recurrence Detection: PET scans can help in finding cancer recurrence after treatment, as increased metabolic activity can signal the return of cancerous cells.
It’s important to note that while PET scans are highly sensitive, they must be interpreted carefully. Noncancerous conditions, such as infections or inflammation, can sometimes mimic the appearance of cancer on a PET scan. Additionally, not all types of cancers are detectable by PET scans. However, PET-CT and PET-MRI scans are effective in detecting many types of solid tumors, including cancers of the:
- Brain
- Breast
- Cervix
- Colorectal area
- Esophagus
- Head and Neck
- Lung
- Lymphatic System (Lymphoma)
- Pancreas
- Prostate
- Skin (Melanoma)
- Thyroid
Heart Disease Assessment
PET scan of the heart
This PET scan image of the heart reveals an area with reduced blood flow, originating from one of the arteries supplying the heart. This crucial information aids doctors in deciding whether interventions like bypass surgery or angioplasty are necessary to restore adequate blood flow.
PET scans play a significant role in evaluating heart health by identifying areas of decreased blood flow within the heart muscle. Reduced blood flow often signifies coronary artery disease, where arteries supplying the heart are narrowed or blocked. The information from a cardiac PET scan is invaluable for patients and their healthcare providers in making critical decisions about treatment strategies, such as:
- Coronary Artery Bypass Surgery: PET scans can help determine if a patient would benefit from bypass surgery to reroute blood flow around blocked arteries.
- Angioplasty: The scan can also indicate the need for angioplasty, a procedure to open clogged heart arteries and improve blood flow.
Brain Disorder Evaluation
PET scans of the brain for Alzheimer’s disease
This comparative PET scan illustrates a typical brain (left) alongside one affected by Alzheimer’s disease (right). The reduction in red color, coupled with an increase in yellow, blue, and green hues, signifies areas of diminished metabolic activity in the brain due to Alzheimer’s disease.
PET scans are also used to investigate various brain disorders by assessing metabolic activity in different brain regions. They can be helpful in evaluating conditions such as:
- Brain Tumors: PET scans can differentiate between benign and malignant brain tumors based on their metabolic activity.
- Alzheimer’s Disease: By detecting patterns of decreased metabolic activity in specific brain areas, PET scans can aid in the diagnosis and monitoring of Alzheimer’s disease and other forms of dementia.
- Seizure Disorders (Epilepsy): PET scans can sometimes identify the areas of the brain causing seizures by showing altered metabolic activity during and between seizure episodes.
Understanding the Risks of a PET Scan
For a PET scan, a small amount of radioactive tracer is injected into your body. While any exposure to radiation carries some risk, the dose from a PET scan tracer is very low, making the overall risk of negative effects minimal. However, it’s important to be aware of potential risks:
- Radiation Exposure to Unborn Babies: If you are pregnant, the tracer could expose your unborn baby to radiation. It’s crucial to inform your healthcare provider if you are pregnant or suspect you might be.
- Radiation Exposure to Breastfeeding Infants: Similarly, if you are breastfeeding, a small amount of the tracer could be passed to your child through breast milk. Discuss this with your provider if you are breastfeeding.
- Allergic Reactions: Although rare, allergic reactions to the tracer are possible. Inform your healthcare provider of any known allergies.
It is essential to discuss any concerns you have about the benefits and risks of a PET scan with your healthcare provider to make an informed decision.
How to Prepare for a PET Scan
Proper preparation is important for ensuring the accuracy and success of your PET scan. Your healthcare provider will give you detailed instructions based on your specific health situation, but general guidelines include:
- Allergy Information: Inform your provider if you have any known allergies, especially to contrast dyes or radioactive substances.
- Medical Conditions and Recent Illnesses: Tell your provider about any recent illnesses or existing medical conditions, particularly diabetes, as they can affect test results.
- Medications and Supplements: Provide a complete list of all medications, vitamins, and herbal supplements you are currently taking.
- Pregnancy and Breastfeeding Status: Inform your provider if you are pregnant or breastfeeding.
- Claustrophobia: If you have a fear of enclosed spaces (claustrophobia), let your provider know. They can take measures to make you more comfortable during the scan.
- Avoid Strenuous Exercise: Generally, you should avoid strenuous physical activity for a couple of days before your PET scan.
- Fasting: Typically, you will need to stop eating for at least four hours before the scan to ensure accurate results. You may be allowed to drink water. Your provider will give you specific fasting instructions.
What to Expect During a PET Scan
The PET-CT or PET-MRI scanner is a large machine that resembles a wide doughnut standing upright. The procedure from start to finish usually takes around two hours and is typically performed on an outpatient basis, meaning you won’t need to stay overnight in the hospital.
Upon arrival for your scan, you may be asked to:
- Change into a Hospital Gown: This helps to ensure no metal interferes with the scan.
- Empty Your Bladder: This can improve image quality and comfort during the scan.
The tracer is then administered by a healthcare professional, usually through an injection into a vein in your arm or hand. You might feel a brief cold sensation as the tracer is injected. After the injection, you will rest quietly in a reclining chair for 30 to 60 minutes. This waiting period allows the tracer to be absorbed by your body and accumulate in areas of metabolic activity.
During the PET Scan Procedure
Once the tracer uptake period is complete, you will be positioned on a narrow, padded table that slides into the scanner opening. It is crucial to remain very still during the scan to prevent blurring of the images. A PET-CT scan typically takes about 30 minutes, while a PET-MRI scan may take around 45 minutes. During the scan, you will hear buzzing and clicking sounds from the machine, which is normal.
The PET scan itself is painless. However, if you experience anxiety about enclosed spaces, you might feel some discomfort while inside the scanner. Inform the nurse or technologist if you feel anxious; they can offer medication to help you relax if needed.
After the PET Scan Procedure
After the PET scan is completed, you can usually resume your normal daily activities, unless your healthcare provider advises otherwise. It’s recommended to drink plenty of fluids after the test to help flush the radioactive tracer out of your body.
Understanding Your PET Scan Results
A radiologist, a doctor specially trained in interpreting imaging scans, will analyze your PET scan images and send a report of the findings to your healthcare provider.
The radiologist may compare your PET scan images with images from other recent tests, such as MRI or CT scans, to get a comprehensive view of your condition. In many cases, the PET images are combined with CT or MRI images (PET-CT or PET-MRI) to provide a more detailed and precise diagnosis. Your healthcare provider will then discuss the results with you and explain what they mean for your health and treatment plan.
Clinical Trials and PET Scans
Explore Mayo Clinic studies of tests and procedures to help prevent, detect, treat or manage conditions, including ongoing research involving PET scan technology and its applications.
Positron emission tomography scan care at Mayo Clinic
Sept. 10, 2024
References
- Positron emission tomography — Computed tomography (PET/CT). Radiological Society of North America. https://www.radiologyinfo.org/en/info.cfm?pg=PET. Accessed April 6, 2021.
- What is PET? Society of Nuclear Medicine and Molecular Imaging. https://www.snmmi.org/AboutSNMMI/Content.aspx?ItemNumber=5649. Accessed April 6, 2021.
- Umterrainer M, et al. Recent advances of PET imaging in clinical radiation oncology. Radiation Oncology. 2020; doi:10.1186/s13014-020-01519-1.
- Adam A, et al., eds. Adrenal imaging. In: Grainger and Allison’s Diagnostic Radiology. 7th ed. Elsevier; 2021. https://www.clinicalkey.com. Accessed April 6, 2021.
- ACR-SPR practice parameters for performing FDG-PET/CT in oncology. American College of Radiology. https://www.acr.org/Clinical-Resources/Practice-Parameters-and-Technical-Standards/Practice-Parameters-by-Modality. Accessed April 6, 2021.
- Cervical cancer. Radiological Society of North America. https://www.radiologyinfo.org/en/info.cfm?pg=cervicalcancer. Accessed April 8, 2021.
- Morrow ES. Allscripts EPSi. Mayo Clinic. April 6, 2021.
- Collins DA (expert opinion). Mayo Clinic. April 24, 2021.
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