Positron Emission Tomography (PET) scans are powerful imaging tests that provide detailed insights into the metabolic activity within your body. Unlike other imaging techniques that primarily show the structure of organs and tissues, a PET scan reveals how these areas are functioning at a cellular level. This capability makes PET scans invaluable for detecting and monitoring a wide range of conditions.
During a PET scan, you will lie on a comfortable table that gently slides into a PET scanner. This doughnut-shaped machine is designed to capture images of the metabolic processes occurring within your body, typically taking around 30 minutes to complete the scan and produce detailed imagery.
A PET scan utilizes a radioactive tracer, a special drug that emits positrons. This tracer is usually injected into a vein and travels through your bloodstream. Areas of your body with higher metabolic activity, often associated with disease, will accumulate more of the tracer. The PET scanner detects the tracer and creates images that highlight these areas of increased metabolic activity. This allows healthcare providers to identify diseases in their early stages, sometimes even before structural changes are visible on CT scans or MRIs. Often, PET scans are combined with CT or MRI scans (PET-CT or PET-MRI) to provide both functional and anatomical information, leading to a more comprehensive understanding of the condition.
Why Are PET Scans Performed?
PET scans are used across various medical specialties to diagnose, monitor, and manage numerous health conditions. Their ability to visualize metabolic activity makes them particularly useful in the following areas:
Cancer Detection and Management
Cancer cells are characterized by their rapid growth and high metabolic rate. This increased metabolic activity causes them to absorb more of the radioactive tracer used in PET scans, making them appear as bright spots in the images. Therefore, PET scans are frequently used in oncology for several crucial purposes:
- Detecting Cancer: PET scans can help identify cancerous tumors throughout the body, sometimes even before they are detectable by other imaging methods.
- Staging Cancer: To determine if and how far cancer has spread from its original site (metastasis). This is critical for determining the appropriate treatment plan.
- Monitoring Treatment Response: PET scans can assess the effectiveness of cancer treatments like chemotherapy and radiation therapy by showing if the metabolic activity of tumors is decreasing.
- Detecting Recurrence: After cancer treatment, PET scans can help identify if the cancer has returned.
It’s important to note that while PET scans are highly sensitive to metabolic activity, some non-cancerous conditions can also cause increased tracer uptake, leading to false positives. Conversely, not all cancers are detectable by PET scans. However, PET-CT and PET-MRI are effective in imaging many solid tumors, including cancers of the:
- Brain
- Breast
- Cervix
- Colon and Rectum
- Esophagus
- Head and Neck
- Lung
- Lymph Nodes (Lymphoma)
- Pancreas
- Prostate
- Skin (Melanoma)
- Thyroid
Assessing Heart Disease
PET scans are also valuable in cardiology for evaluating heart health. They can identify areas of the heart muscle that are not receiving enough blood flow, a condition known as myocardial ischemia. This is crucial in determining the extent and severity of coronary artery disease. Specifically, PET scans of the heart are used to:
- Evaluate Blood Flow: Detect areas of reduced blood flow to the heart muscle, indicating potential blockages in the coronary arteries.
- Assess Myocardial Viability: Determine if damaged heart muscle is still alive and potentially recoverable, which helps guide decisions about procedures like coronary artery bypass surgery or angioplasty.
- Plan Treatment Strategies: The information from a PET scan can help doctors decide if interventions like bypass surgery or angioplasty are likely to be beneficial for restoring blood flow to the heart.
Investigating Brain Disorders
In neurology and psychiatry, PET scans play a role in evaluating various brain disorders by measuring brain activity. They are used to investigate conditions such as:
- Alzheimer’s Disease and other Dementias: PET scans can detect patterns of decreased metabolic activity in specific brain regions associated with Alzheimer’s disease and other forms of dementia, aiding in diagnosis and differentiation.
- Brain Tumors: Similar to cancer detection elsewhere in the body, PET scans can help locate and assess the metabolic activity of brain tumors.
- Seizure Disorders (Epilepsy): PET scans can help identify areas of the brain responsible for seizures, which can be useful in planning surgical treatment for epilepsy.
Understanding the Risks of PET Scans
While PET scans are generally safe procedures, they do involve a small amount of radiation exposure from the radioactive tracer. However, the dose is low, and the risk of long-term effects is minimal. Potential risks include:
- Radiation Exposure to Unborn Babies: Pregnant women should avoid PET scans due to the potential risk of radiation exposure to the fetus.
- Radiation Exposure to Breastfeeding Infants: Breastfeeding mothers may need to temporarily interrupt breastfeeding after a PET scan to minimize radiation exposure to the infant.
- Allergic Reactions: Although rare, allergic reactions to the tracer are possible.
It’s important to discuss the benefits and risks of a PET scan with your healthcare provider to make an informed decision.
Preparing for a PET Scan
Preparation for a PET scan typically involves a few key steps to ensure the best possible image quality and minimize any potential discomfort. Your healthcare provider will give you specific instructions, but general guidelines include:
- Informing Your Doctor: Tell your doctor about any allergies, medical conditions (especially diabetes), medications, vitamins, or herbal supplements you are taking. Also, inform them if you are pregnant or breastfeeding, or if you have claustrophobia.
- Fasting: You will usually be asked to fast for at least four hours before the scan to ensure accurate results.
- Avoiding Strenuous Exercise: Avoid intense physical activity for a couple of days before the scan.
What to Expect During a PET Scan
The PET scan procedure itself is generally straightforward and painless:
- Arrival and Preparation: You may be asked to change into a hospital gown and empty your bladder upon arrival.
- Tracer Injection: A healthcare professional will inject the radioactive tracer into a vein in your arm or hand. You may feel a brief cold sensation.
- Waiting Period: You will rest quietly for 30 to 60 minutes while the tracer distributes throughout your body.
- Scanning: You will lie on a narrow table that slides into the PET scanner. It’s crucial to remain still during the scan, which takes about 30-45 minutes, to prevent blurred images. The scanner may produce buzzing or clicking sounds.
- Claustrophobia Management: If you are claustrophobic, inform the staff. Medication to help you relax can be provided.
After the PET Scan
After the scan, you can usually resume your normal activities unless instructed otherwise by your doctor. Drinking plenty of fluids will help flush the tracer out of your system.
Understanding Your PET Scan Results
A radiologist, a doctor specialized in interpreting medical images, will analyze your PET scan images and send a report to your healthcare provider. The radiologist may compare your PET scan with other imaging studies, like CT or MRI, for a comprehensive assessment. The combined information helps in accurate diagnosis and treatment planning.
Clinical Trials and PET Scans
PET scan technology is continuously being researched and refined. Clinical trials are ongoing to explore new applications of PET scans in preventing, detecting, treating, and managing various diseases.
Explore Mayo Clinic studies of tests and procedures to help advance medical knowledge and patient care.
By Mayo Clinic Staff
Positron emission tomography scan care at Mayo Clinic
Sept. 10, 2024
References
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- 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.
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- Collins DA (expert opinion). Mayo Clinic. April 24, 2021.
