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PET Scans: Get the Facts

PET Scans: Get the Facts

What are PET scans?
Positron emission tomography (PET)—also called PET imaging or a PET scan—is a noninvasive, painless molecular imaging technology that allows physicians to determine how organs and tissues inside the body are functioning on a molecular and cellular level. PET is a powerful diagnostic tool that is advancing our understanding of the underlying causes of disease and improving the way in which many diseases are detected and treated.

How do PET scans work?
When disease strikes, the biochemistry of an individual's tissues and cells changes. In cancer, for example, cells multiply at a much faster rate than normal cells, feeding on sugars like glucose.

If an individual has cancer or cancer is suspected, a nuclear medicine or molecular imaging specialist performs a PET scan to see exactly what is going on inside that person's body. During a PET scan, a patient is injected with a very small amount of a radiotracer such as fluorodeoxyglucose (FDG), which contains both sugar and a radioactive element. The radiotracer travels through the body and is absorbed by the tissues or the organ being studied. The patient then lies down on an examining table and is moved to the center of a PET scanner. The scanner contains an array of detectors that receive signals emitted by the radiotracer. Using these signals, the PET scanner measures metabolic activity while a computer reassembles the signals into images.

Who gets PET scans and why are they useful?
PET scans are one of the most effective types of nuclear medicine procedures for detecting cancer, brain disorders, heart conditions and other diseases.

Cancer—PET is a powerful tool for diagnosing and determining the stages of many types of cancer, including lung, head and neck, colorectal, esophageal, lymphoma, melanoma, breast, thyroid, cervical, pancreatic and brain cancers.

The National Oncologic PET Registry (NOPR)—a nationwide database documenting cases in which PET has been used by physicians to more successfully manage disease in patients—shows that in more than one out of three cases, the use of PET prompts changes to the management of patient care. The results, published in The Journal of Clinical Oncology, demonstrate the vital role that PET can play to properly diagnose or verify the suspected recurrence of disease.

PET scans can eliminate the need for surgical biopsy because PET can detect whether lesions are benign or malignant. PET is currently the most effective way to check for cancer recurrence. It can also be used to determine whether chemotherapy or other treatments are working as intended, as well as to help individuals avoid unnecessary or unproductive surgery or treatment.

Brain disorders—PET scans can detect the onset of neurological disorders such as Alzheimer's disease and other memory disorders. Early detection can give patients access to therapies that are more effective in the beginning stages of the disease. For epilepsy patients, PET is one of the most accurate methods available to pinpoint areas of the brain causing epileptic seizures and for determining whether surgery is an option for treatment.

Heart problems—In addition, PET scans can detect cardiovascular diseases such as coronary artery disease and heart damage following a heart attack. PET scans can pinpoint areas of decreased blood flow, such as those with blockages, and differentiate living muscle from damaged muscle. This information is particularly important for patients considering procedures such as angioplasty or coronary artery bypass surgery following a heart attack.

What advantages do PET scans offer over other imaging technologies, such as computed tomography (CT) or magnetic resonance imaging (MRI) scans?
Unlike CT or MRI scans, PET scans can measure cellular-level metabolic changes occurring in an organ or tissue. This gives PET an advantage over other technologies in determining whether lesions in the body are benign or malignant, eliminating the need for surgical biopsies if PET scans are negative. In addition, PET can detect diseases at their earliest stages, since disease processes often begin with functional changes at the cellular level. CTs or MRIs usually cannot detect changes until diseases begin to cause changes in the structure of organs or tissues. A PET scan is often used in conjunction with an MRI or CT scan to give a full three-dimensional view of an organ and the location of cancer within that organ.

What are the risks involved in getting a PET scan?
The risks involved with PET scans are minimal, with the benefits often far outweighing the risks. In fact, PET scans can eliminate the need for exploratory tests and help individuals avoid potentially expensive and invasive surgeries later. During PET scans, patients are exposed to radioactive material, but in very low doses that do not affect normal bodily functions. Pregnant or breastfeeding women may expose their fetuses or infants to radiation through PET and should discuss the risks and benefits with their doctors before having the tests performed.

How often is PET used?
PET has advanced greatly since it was introduced in the 1970s, and PET scans are more and more widely used. In 2005, an estimated 1,129,900 clinical PET patient studies were performed at 1,725 sites around the country.

How should a patient prepare for a PET scan?
PET scans are usually performed on an outpatient basis, and doctors will provide patients with detailed instructions on how to prepare for an exam. Most patients are asked not to eat or drink anything for a minimum of six hours before PET is administered. Patients should inform their doctors of any medications they are taking or any ongoing medical conditions. Patients should wear loose, comfortable clothing and may be asked to wear hospital gowns during a PET scan.

What should a patient expect during the procedure?
The procedure begins with the injection of a radiotracer into the patient's vein. Once the radiotracer is injected, it takes about 45 minutes to an hour for the body to absorb it. Next, the patient lies down on a flat examining table that is moved to the center of the PET scanner. The machine detects and records the signals from the radiotracer. This process can take another 30 to 60 minutes. A computer is used to convert the signals into three-dimensional images that physicians can look at to detect any problems.

How long does it take to get results?
A physician trained in nuclear medicine will interpret the results and write a report for the physician who ordered the tests. A verbal report can usually be given to the referring physician the same day and the written report is usually delivered to the physician within two or three days.

How much do PET scans cost, and are they reimbursed by insurance companies?
PET scans range from $850–$4,000, depending on the type of scan. Insurance companies will cover the cost of PET scans for certain types of cancer. Through NOPR, CMS is evaluating data to consider expanding coverage for other types of cancer. Because of the mounting evidence of the effectiveness of PET for the diagnosis and treatment of a wide range of cancers, coverage levels continue to expand. For the most updated figures, check with your insurance carrier or physician, as the levels at which Medicare reimburses for PET are under review with CMS and subject to change.

To learn more about PET scans or other nuclear medicine techniques, visit the SNM PET Center of Excellence.