Positron Emission Tomography
PET imaging (Positron Emission Tomography) gives us a non-invasive method to look at the glucose metabolism of every cell in our bodies. This is used mostly for cancer patients, but PET is also one of the gold standards for the earliest detection of Alzheimer’s Disease and other types of dementia.
PET uses blood glucose with a small radioactive particle called a positron emitter chemically bonded to it allowing us to see where the glucose is being metabolized. Since most cancer cells have a much higher metabolic rate than the surrounding tissue, it stands out like a light bulb in a dimly lit room. And since our highly specialized PET/CT scanner images the patient for both CT & PET while in the same place in space, it gives a complete picture of both anatomic and metabolic information to the oncologist simultaneously. These new technologies working together give our oncologists better tools to fight cancer.
Many times, the entire tumor shows the same density when using structural imaging alone, even though some of the tumor may be inactive. PET gives us metabolic data showing where disease might be hiding. But it cannot pinpoint the exact structure of this small area. PET and CT together give all the information. It may even show us that only part of the tumor is active disease, while the rest is scar tissue that has the same structural density. This can identify different parts of the tumor that are more active than others.
How PET helps in diagnosis and disease stage
If a PET/CT is used to locate the disease, the physicians have a metabolic map to guide them in determining if the suspected tissue is truly diseased, as well as guiding them through the biopsy process to identify it for future treatment option decisions.
PET helps the physician know the extent of the disease process, such as defining if the tumor is isolated or if cells have migrated to the lymph nodes. This information is critical in determing the most effective treatment option.
PET/CT software also has the ability to measure the amount of glucose in the diseased tissues. If after the initial scan the oncologist decides that chemo-therapy is the best treatment, you can be brought back during chemo-therapy to see if the glucose metabolic rate of the diseased cells has decreased. These subtle changes can tell the oncologist how well the therapy is working and decide if the current plan is ideal or if changes need to be made.
PET/CT for detecting Alzheimer's and other types of dementia
PET is also used for the early detection of Alzheimer’s and other types of dementia such as frontal lobe dementia. Since the treatment of these two diseases is handled differently, telling them apart from each other is critical.
Because the brain almost exclusively uses glucose for energy, the glucose gets taken up by the brain at high levels. To diagnose dementia's like Alzheimer's, instead of looking for a light bulb in a dimly lit room, we are looking for a dark corner in a room full of light. These areas represent parts of the brain that no longer function at the same level as the rest of the brain.
How to prepare
You'll be asked to not eat for at least six hours before the exam, but you'll need to stay well hydrated. Since we administer a glucose molecule, this fasting time assures the glucose gets taken up by the cells instead of being stored for later use. On the day of the exam it's also important to stay as relaxed as possible to minimize brain stimulus.
How the procedure is performed
After arriving at the PET/CT department, you'll be escorted to an exam room where you can sit in a large, comfortable recliner. The technologist will explain the procedure and ask you a few questions. A current blood glucose reading is then taken to make sure it is within normal parameters. An IV is administered with a small amount of normal saline given to keep you hydrated.
You'll be asked to relax in the room for approximately 30 minutes. To limit brain stimulus, you'll sit in a recliner with a warm blanket and dim lights. After you're relaxed, the PET glucose molecule will be administered through your IV. You'll remain in this environment for approximately 30 minutes so the glucose can be taken up evenly by your brain cells.
Then, you'll go to the scanner for the imaging. You'll be made comfortable on the imaging bed with your head in a special holder to assure stability and non-motion. It is not necessary to hold your breath, you simply just need to relax in one position and listen to soothing music. The scan takes about 15 minutes.
Your PET exam results are sent within two working days to your referring physician who will then contact you within one week of receiving the results.