From Southwest Health, Nov/Dec 2006: Q: My husband is scheduled for a PET scan. What is it? A: PET stands for positron emission tomography. Positrons are tiny particles emitted (sent out) from a radioactive substance. Each organ in your body metabolizes (uses) different substances at different rates. Your husband will be given the substance that will give the best results for the part of the body that will be scanned. The scanner measures the emissions from the positrons. A computer uses these measurements to create an image or picture. PET scans are most often used to detect cancer. They are also used to check the effects of cancer therapy. PET scans of the heart can help diagnose or evaluate heart health or function. In the brain, PET scans are useful for evaluating memory disorders, brain tumors, or seizures. You will be given detailed instructions of how to prepare. Generally, plan on wearing loose-fitting clothing and not eating for four hours before the scan.

A PET scan is usually just one of many tests your doctor has ordered to evaluate your health. PET scans will compared with all of your other test results for the most complete picture of your health.

Because PET can evaluate body function, it can detect changes in your body's chemical makeup before there are physical changes that show up in other radiology images, such as X-ray, CT, or MRI. Comparing a PET scan with these images gives your doctor the best information about your health.

PET can give false results if your body's chemical balance is not normal. Your technologist will ask you questions to help identify possible chemical imbalance.

The "secret" ingredient
Before your scan, you will receive a radioactive substance that is tagged or attached to a natural body compound. Usually that's glucose, but it could be water or ammonia.

Once in your body, the radioactive compound finds its way to your tissues and organs and can be seen by the PET scanner.

Different colors or brightness on an image show different levels of function in tissues or organs.

The radioactive substance is usually given through an intravenous injection. It is sometimes given as a gas. You will be asked to rest quietly, to limit moving and talking, which may affect how your body absorbs the substance. After about 35 to 45 minutes, you're ready to be scanned.

You should drink plenty of fluids after the procedure to help flush the radioactive substance from your body. The amount of radioactivity is very small and easily flushed from your body.

Scanning for cancer
Scanning for cancer is the most common type of PET scan. Cancer cells are greedy eaters, absorbing glucose at a much higher rate than their normal neighbors. This higher absorption of radioactively-tagged glucose makes the cancer cells appear much brighter than the surrounding tissue.

PET scans are sometimes used during or after cancer treatment to see how successful the therapy has been and to help make decisions about future care. These scans can be performed on the whole body.

Scanning the heart
A PET scan of the heart can help evaluate blood flow to the muscle of the heart or look for signs of coronary artery disease. This information can help your doctor decide whether you would benefit from an angioplasty or coronary artery bypass surgery to restore blood flow.

Heart scans can also show if there is healthy or scarred heart muscle in an area that has suffered a myocardial infarction (heart attack).

Scanning the brain
PET scans of the brain may be helpful in evaluating patients who have memory disorders of an unknown cause or patients with seizures that have not responded to medical therapy. The scans can help evaluate whether there are brain tumors and provide information about the tumor.

How do I know what kind of scan I need?
Your doctor knows the result he or she needs and will order the test he/she believes will give the best result. A radiologist (a physician who specializes in imaging technology) reviews the test request and confers with your doctor if the radiologist believes another test might be better.

When your scan is done, a radiologist who specializes in nuclear medicine will read the scans and send a report to your doctor.

Scheduling your test
The radioactive substance you receive has a very short life. It must be made in a laboratory close to where the procedure is performed. At Southwest, the substance is flown in just before it is needed.

It is important that you are on time for your appointment. You must receive the substance at the scheduled time for the most accurate results.

What are the risks?
Because the radioactivity you receive has a very short life span, your radiation exposure is low. The amount you receive is so small that it does not affect your normal body function.

There is risk of radiation exposure to fetuses in pregnant women or to the infants of women who are nursing. Your imaging team will ask you questions to determine whether you may wish to decline or postpone a PET scan. If you are not asked, you should inform your imaging team if you are pregnant or nursing.

More information on diagnostic imaging.