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PET Overview
Positron Emission Tomography (PET)
PET is a state-of-the-art nuclear medicine study that produces pictures of the body’s sugar metabolism. Unlike computed tomography (CAT or CT) images or magnetic resonance imaging (MRI), which create images of the size and structure of internal organs, PET/CT creates images that show the differences tissue metabolism. This is particularly useful in assessing certain types of cancers, heart disease, and brain disorders since changes in metabolism often occur well before changes in size or structure.
Understanding PET/CT Technology
As the food we eat digests, the body converts much of the nutrients into fuel (sugars and proteins) that can be used by individual cells and used as energy to generate new cells. This process is called metabolism. By using special drugs called tracers that mimic the normal nutrients the body uses as fuel (for example, sugar or oxygen), we can view this process and actually see areas of abnormal metabolism. The most common drug used as a tracer is known as FDG.
For example, we know that cancer cells metabolize very rapidly, using a greater amount of fuel and causing tracer to accumulate in these cells. Conversely, scar and non-living tissue use no energy; therefore no tracer will accumulate in these areas. The scanner will detect the tracer as it sends signals from the body, creating a picture that shows both normal and abnormal cellular activity. Your physician will have the help of a specialized physician, either a Radiologist or Nuclear Medicine physician, to read and interpret this metabolic information.
Since changes in cellular activity often occur before any structural changes are able to be detected, PET/CT can help your physician make an earlier diagnosis, or assessment of therapy. In many cases, this means a faster, more effective treatment and can result in a better outcome (prognosis) for you.
How PET/CT is Used
Positron Emission Tomography (PET) is most commonly used in oncology to determine if a patient has cancer, the extent of the disease, or to assess the effectiveness of a treatment. PET/CT aids physicians in:
- Visualizing small tumors (possibly smaller than ¼ of an inch) to allow for early diagnosis
- Determining if the cancer has spread for the selection of the most appropriate treatment (this process is called staging)
- To verify the effectiveness of a therapy or treatment
- Detecting recurrence of cancer
PET in oncology provides your physician with highly accurate information about cancer and its location that can influence their care management decisions. Using PET/CT may result in more effective therapies and improved outcomes, while possibly avoiding more invasive exams or surgeries.
In cardiology, PET/CT is considered the “Gold Standard” for assessing the health of heart tissue prior to surgery. By viewing the rate of metabolism in different areas of the heart, physicians can tell whether improving the blood flow to damaged areas will improve the patient’s condition. Low or no metabolism in an area of the heart usually means that the damage to the heart is permanent and that risk of surgery may not produce any benefits to the patient.
In neurological applications, PET/CT can show unusual metabolism in the brain which can help diagnose certain neurological disorders such as epilepsy, Parkinson’s disease, Alzheimer’s disease, and other dementias. Particularly of use, PET/CT is able to detect areas of abnormal metabolic brain activity and localize seizure foci in patients with uncontrollable epileptic seizures to help determine whether surgery is a viable option.
Earlier and more accurate diagnosis of neurological disorders may result in a prolonged improvement in the quality of life for these patients.
Positron Emission Tomography (PET) is not appropriate for every patient nor every condition. Patients should talk to their physician to determine if PET/CT is right for you.
FDG (18F-Fluoro-2-deoxyglucose)
FDG is the tracer drug, or radiopharmaceutical, that is used to measure metabolism in nearly all clinical Positron Emission Tomography (PET) studies. FDG is a simple sugar attached to a short-lived radioactive particle. The amount of radiation received by a patient during a PET/CT is quite small and is similar to that of a CT scan or spinal x-ray. The total volume of drug injected is typically less than 1/10 of an ounce (roughly 1-3 cubic centimeters). The Federal Food and Drug Administration (FDA) considers FDG to be safe and 24 hours after the PET/CT study the FDG is completely broken down and expelled from the body through the urine.
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