PET Scans: Seeing Your Body Cells at Work

Patient Expert

When I was diagnosed with inflammatory breast cancer in 1998, the first thing my doctors did was order a battery of tests to see if the cancer had spread.   The test they did NOT order was a PET scan.   Positron emission tomography (PET) was still very expensive and not easy to read. The machine that combined the PET scan with the CT scan went into clinical use at the University of Pittsburg in 1998.   Because it was so effective, TIME magazine called it the medical invention of the year in 2000.   So for years I read about other people's experiences with PET scans, but never needed one myself until last fall.

Why have a PET scan when there are so many other ways that doctors can look at our innards these days?   The PET is useful because it doesn't look at the body's structures.   It looks at how our body metabolizes sugar.   Cancer cells greedily grab all the nourishment they can find because they are reproducing much faster than the normal body cells.   The PET picks up these areas of higher metabolism.

For breast cancer patients, a PET may be ordered as part of initial staging if the doctor is worried that the cancer has already spread, as part of treatment to see if a particular chemo or other treatment is shrinking a tumor, or as part of follow-up care.   Because the test is expensive and time-consuming, your doctor may prefer to use other types of imaging tests, especially because PET scans can be prone to false positives.   But when another test picks up an area of concern, the PET/CT scan can be useful.   It is not useful for routine screening because it does not pick up the tiniest spots of cancer.

I had my PET scan to find out if a nodule near my lung was benign or malignant.   It was in a place that would be difficult to biopsy, and the oncologist and radiologist thought a PET could help determine what it was.   If you need a PET scan, your experience will probably be similar, but there may be some differences depending on the area the doctor wants to see.   PET scans can also be used for other diseases besides cancer, so again the overall procedure will be similar, but perhaps not identical.

Before the test I was told not to eat or drink anything but water.   Drinking lots of water is a good idea because it will hydrate your veins and make it easier to insert the IV.   You are not allowed to eat because if your body is digesting food, those places will light up on the images.   The technicians at the imaging center asked the usual preliminary questions about allergies and medications, but there were some extra questions about whether I was diabetic.   If you are diabetic, it is important to discuss your condition with your doctor because of the fasting related to the test and the administration of glucose you are going to receive.   It is also essential to let the doctor know if you might be pregnant.

The technician took me into a small room and settled me into a comfortable chair.   She checked my blood sugar level, and then she inserted the IV and injected glucose with a radioactive tracer.   In some cases you may be asked to swallow or inhale the tracer.   Then she left me to read my book or watch the TV.   It is important to be still while the glucose goes through your body.   If you are exercising, even a soothing activity like knitting, the sugar is going to go to those muscles and throw off the test.   So take a good book or your favorite music and prepare to settle in for about an hour.

It is normal to be anxious about a PET scan. After all your doctor is testing to see if a specific worrisome spot is cancer or if your cancer has spread to new areas as yet unsuspected.   If you are also afraid of needles or small spaces, your anxiety may be even higher.   Don't hesitate to ask your doctor if it would be OK to take an anti-anxiety medicine if you are concerned that you might have a panic attack.     However, the test itself is really not that bad.

Once I rested for an hour (your time may vary depending on what the doctor is looking for), I went to the room next door that had the actual PET machine.   It is a large metal square with a round hole in the middle.   I lay on an narrow table that went into the hole.   The technician covered me with a warm blanket, adjusted a pillow under my knees and straps to keep my arms from flopping off the table, and I was ready to ride.   As the table slowly went through the round hole, called a gantry, my body was sending out signals, and the machine was picking them up and making pictures for the radiologist to read.

The gantry in   PET scan is much larger and shorter than the one used for a MRI, so most people will not have trouble with claustrophobia during a PET.   The hardest part is lying still.   As soon as someone tells me to not to move, my nose starts to itch.   However, I imagined myself sunning on the beach and closed my eyes.   This part of the test took about 30 minutes, but again your time may be different.

Before I left, I double checked about which doctors would receive the report and when I would hear the results.   After I have any test, I always ask when and who I should call if I have not heard within the expected time frame.   Usually, the answer is to call the doctor who ordered the test, but it is always a good idea to have the details confirmed before you leave the testing center.

Then the worst part of any diagnostic test began the waiting for results.   I was shocked when the results came back "inconclusive."   I had the impression that PET scans were the latest in the most definitive results.   They may be that, but they do have limitations.   A spot of cancer can be too small to show up, or the degree of glucose uptake may be in a range that could be cancer or could be normal.   An area could show more activity because you were moving or had recently eaten.

So we were back to the original question.   Should the spots near my lung and on my shoulder blade be biopsied, or should we wait, watch, and repeat the tests?   My oncologist thought a nodule the size of the one near my lung would probably light up on the PET scan if it were cancer.   He decided the best course of action was to repeat the CT and bone scans in four months.   When we did that, the spots had not grown, so my doctor felt comfortable saying I don't have a metastasis.   He also said, "Let's do it again   in four more months to be sure."

As a cancer patient, you will probably have a variety of types of tests along the way.   Each will have limitations and benefits.   It is a good idea to ask your doctor:   What can this test show?   How will the information from the test affect my treatment?   Are there other methods to learn the same information with a less invasive test?   Modern imaging tests can spare many patients biopsies or even extensive exploratory surgery.   From the mammogram your doctor used to assess your initial breast symptoms through to complicated nuclear medicine tests, your doctor has many tools to guide your treatment.

Other shareposts on some of the imaging tests your doctors might use:

MRI's as Part of Your Follow-up Care

Screening Breast MRI's:   Should You Get One?

Bone Scans:   Seeing Your Skeleton

CT Scans:   Getting a Good Picture

New Ultrasound Approved for Dense Breast Screening