Positron emission tomography (PET scan) is an imaging test used to generate cross-sectional and three-dimensional pictures of the human body. Unlike other imaging tests, the images produced by positron emission tomography are not detailed renderings of internal body structures. PET scan images use color variations to provide information about chemical activity within the body’s organs and tissues. Most imaging tests show how the human body looks. PET scans show what the human body is doing. As a result, positron emission tomography is the only imaging test that can distinguish a benign (non-cancerous) tumor from a malignant (cancerous) tumor.
Positron emission tomography is used to diagnose and monitor cancer, as well as heart disease, certain infections, inflammatory diseases, neurological diseases, and a myriad of other disorders.
How Does Positron Emission Tomography Work?
Before a PET scan test, a radiotracer containing small amounts of radioactive isotopes is injected into the patient’s bloodstream. These isotopes are designed to target specific organs, tissues, and other internal body structures. For example, the radiotracer 11C-acetate is exclusively absorbed by the kidneys and prostate. Once the radiotracer has been absorbed, a special camera in the PET scanner takes pictures of the radiotracer inside its targeted structure/s.
How is Cancer Diagnosed with a PET Test?
Positron emission tomography can help physicians evaluate the following:
- Extent of tumor metastasis (spread)
- Response to treatment
- Tumor recurrence after treatment
Cancer cells use more energy than normal tissues. Therefore, cancer appears “hot” or bright in a PET scan. Malignant (cancerous) cell growth is characterized by cellular division, metastasis (spread), and/or invasion without order. This aggressive behavior forces the body to supply cancer cells with ever-increasing amounts of nutrients. As a result, chemical activity in around cancer cells is uniquely observable with positron emission tomography.
Preparing for a PET Scan
Before a PET scan, your doctor will review any instructions and/or prerequisites pertaining to your test. In most cases, patients are asked to fast for 4 to 6 hours before the test. If the heart is being scanned, patients are asked not to consume caffeine for 24 hours prior to the test.
Discuss any medications, herbal supplements, and/or illicit drugs that you are taking prior to your PET scan. Certain substances in the body may inhibit the PET scanner’s ability to generate accurate images.
What to Expect During a PET Scan
Once you are inside the examination room that houses the pET scanner, you will be asked to lie down on a narrow examination table. On the examination table you will be injected with a radiotracer in the hand or forearm. In 30 to 60 minutes, depending on the targeted internal body structure, the radiotracer will be absorbed and ready for imaging. Meanwhile, you will be asked to relax and avoid talking. Movement may inhibit proper distribution of the tracer through the bloodstream.
After you’ve been given the radiotracer, the examination table is slid into the center of the PET scanner. If you are claustrophobic or if you have difficulties sitting still for long periods of time, you may be given a mild sedative before the test.
Duration: A PET scan takes about 30 to 45 minutes.
PET Scan Side Effects
The radiotracers associated with positron emission tomography contain negligible amounts of ionizing radiation. As a result, radiation poisoning cannot occur during a PET scan. There are no known long-term side effects associated with positron emission tomography.
Short-term side effects, however, may occur:
- Allergic Reactions: Certain radiotracers may provoke an allergic reaction. This is extremely rare, usually mild, and almost always subsides within minutes.
- Slight Pain: The injection of the radiotracer may cause slight pain at the site of injection.
- Hot Flashes: Depending on the radiotracer, the patient may experience brief and mild hot flashes during the test.
PET Scan Risks
Pregnancy: Women who are pregnant or breastfeeding may not be candidates for positron emission tomography. Radiotracers may interfere with fetal development and/or introduce potentially harmful substances into the breast milk.
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- Miele, Evelina. Journal of Experimental and Clinical Cancer Research. 2008. Retrieved on April 20, 2009 from.