Positron Emission Tomography (PET) is a major diagnostic imaging modality used predominantly in determining the presence and severity of cancers, neurological conditions, and cardiovascular disease. It is currently the most effective way to check for cancer recurrences and it offers significant advantages over other forms of imaging such as CT or MRI scans in detecting disease in many patients.
PET images demonstrate the chemistry of organs and other tissues such as tumors. A radiopharmaceutical, such as FDG (fluorodeoxyglucose), which includes both sugar (glucose) and a radionuclide (a radioactive element) that gives off signals, is injected into the patient, and its emissions are measured by a PET scanner.
A PET scanner consists of an array of detectors that surround the patient. Using the gamma ray signals given off by the injected radionuclide, PET measures the amount of metabolic activity at a site in the body and a computer reassembles the signals into images. Cancer cells have higher metabolic rates than normal cells, so they show up as denser areas on a PET scan. PET is useful in diagnosing certain cardiovascular and neurological diseases because it highlights areas with increased, diminished or no metabolic activity, thereby pinpointing problems.
Because PET measures metabolism, as opposed to MRI or CT, which image "structure", it can be superior to these modalities, particularly in separating tumor from benign lesions, and in differentiating malignant from non-malignant masses such as scar tissue formed from treatments like radiation therapy.
PET is often used in conjunction with a CT scan through "fusion" to give a full three-dimensional view of an organ and the location of cancer within that organ. The newest PET scanners are a combination of PET and CT devices that provide the important metabolic information from PET superimposed on the high-quality anatomic information from CT.
PET/CT procedures are widely available today. The technology is robust and provides high-quality images.
PET is considered particularly effective in identifying whether cancer is present or not, if it has spread, if it is responding to treatment, and if a person is cancer free after treatment. Cancers for which PET is considered particularly effective include lung, head and neck, colorectal, esophageal, lymphoma, melanoma, breast, thyroid, cervical, pancreatic, and brain as well as other less-frequently occurring cancers.
Early Detection: Because PET images biochemical activity, it can accurately characterize a tumor as benign or malignant, thereby avoiding surgical biopsy when the PET scan is negative. Conversely, because a PET scan images the entire body, confirmation of distant metastasis can alter treatment plans in certain cases from surgical intervention to chemotherapy.
Staging of Cancer: PET is extremely sensitive in determining the full extent of disease, especially in lymphoma, malignant melanoma, breast, lung, colon and cervical cancers. Confirmation of metastatic disease allows the physician and patient to more accurately decide how to proceed with the patient's management.
Checking for recurrences: PET is currently considered to be the most accurate diagnostic procedure to differentiate tumor recurrences from radiation necrosis or post-surgical changes. Such an approach allows for the development of a more rational treatment plan for the patient.
Assessing the Effectiveness of Chemotherapy: The level of tumor metabolism is compared on PET scans taken before and after a chemotherapy cycle. A successful response seen on a PET scan frequently precedes alterations in anatomy and would therefore be an earlier indicator of tumor response than that seen with other diagnostic modalities.
PET's ability to measure metabolism also has significant implications in diagnosing Alzheimer's disease, Parkinson's disease, epilepsy and other neurological conditions, because it can vividly illustrate areas where brain activity differs from the norm.
Until recently, autopsy has been considered the only definitive test for Alzheimer's disease (AD). Recent studies indicate that PET can supply important diagnostic information and confirm an Alzheimer's diagnosis. When comparing a normal brain versus an AD-affected brain on a PET scan, a distinctive image appears in the area of the AD-affected brain. This pattern is seen very early in the AD course. Conventionally, the confirmation of AD is a long process of elimination that averages between two and three years of diagnostic and cognitive testing. Early diagnosis can provide the patient access to therapies, which are more effective earlier in the disease.
PET also is useful in differentiating Alzheimer's disease from other forms of dementia disorders, such as vascular dementia, Parkinson's disease, Huntington's disease, etc.
PET is also one of the most accurate methods available to localize areas of the brain causing epileptic seizures and to determine if surgery is a treatment option.
Several days prior to your appointment you will be contacted and given instructions regarding fasting, medications, and exercise. You will be asked to refrain from eating for 4 -6 hours before your scan. This includes chewing gum, cough drops, and candy of any kind. You are allowed to drink water at this time. In fact, extra water intake is encouraged on the day before and the day of your scan. Diabetic patients should check with their physician for additional instructions. No strenuous exercise will be allowed 24 hours prior to your scan. No jogging, shoveling, raking, heavy lifting, bicycling, etc.
We encourage you to wear comfortable clothing without buttons or zippers to your appointment. You will not be required to disrobe, but you will be asked to remove jewelry and metal objects such as belt buckles, keys, coins, and money clips.
Your technologist will explain the procedure, discuss symptoms (if any) along with medical history and start an IV in vein in the arm (or hand). Seated in a reclining chair, your blood sugar will be checked with a finger stick as it is important to know your blood sugar level prior to the procedure.
A small amount radioactive tracer called 18F- FDG is injectedted through your IV . You will be asked to relax for 45-60 minutes following this injection with as little stimulation as possible to allow for proper absorption of the material. Following this period of resting, you will be escorted to the rest room to empty your bladder before your scan.
Your Nuclear Medicine Technologist will assist you onto the PET/CT Scanner and position you for your exam. The scan will take approximately 30 minutes. For maximun comfort, a pillow is placed under the head and the knees and you are covered with a warm blanket. Your arms will rest comfortably above your head.
Once the images are complete, your Technologist will evaluate the images for quality, remove your IV, address any issues or concerns that you may have and escort you back to the reception area. The images are read by a Radiologist and the results are sent to your ordering physician. The ordering physician will provide results to you.
You should not experience unusual side effects after your PET/CT scan. If you do, please contact your doctor immediately. Since you were injected with a radioactive tracer, the tracer may remain in your body for approximately 12 hours after your procedure and continuing to emit low levels of radiation. In order to reduce the amount of radiation exposure to both you and those around you, we advise all patients who have had a PET/CT scan to take the following steps for approximately 12 hours following their procedure:
If you have any questions or concerns regarding a PET/CT appointment, please contact us at (603) 740-2588.
Wentworth-Douglass Hospital
789 Central Avenue
Dover, New Hampshire 03820
Phone: (603) 742-5252
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