Positron Emission Tomography (PET) is an imaging technique which allows the demonstration of the functional chemistry of body organs and other tissues such as tumours. PET is rapidly becoming a major diagnostic imaging modality in determining the presence and severity of cancers, neurological conditions and cardiovascular diseases.
A whole body PET scan can be combined with a whole body CT scan with intravenous/oral/rectal contrast as per the need of the patient. Adding a diagnostic CT scan can greatly enhance the diagnostic capabilities of both imaging techniques.
How does it work?
A radiopharmaceutical, such as FDG (fluorodeoxyglucose), that gives off gamma ray signals, is injected into the patient and its emissions are detected by a PET scanner. It measures the amount of metabolic activity at various sites in the body and a computer reassembles the signals into images.
Cancer cells have higher metabolic rates than normal cells, and show up as denser areas on a PET scan. It is useful in diagnosing certain cardiovascular and neurological diseases because it highlights areas with increased, diminished or no metabolic activity.
What preparations are needed for undergoing a PET-Scan?
For a PET-CT scan a patient needs to spare approximately 2-3 hrs. He/She should report to the PET CT facility essentially after prior appointment in a fasting state of approximately 6 hrs. In case of diabetics, the blood sugar levels should be controlled so that the fasting blood sugar is less than 175 mg/dL. The PET scan may be non-conclusive if performed under higher blood sugar levels.
How can a PET scan make a difference in cancer management?
PET being a metabolic imaging tool, can characterize a tumor as metabolically active or inactive, thereby obviating the need for surgical biopsy when the PET scan is negative. In case of active metabolism in a tumor, it helps in localizing the site of disease for accurate tissue sampling.
A PET scan facilitates the demonstration of abnormal metabolism in cancer cells when there is no anatomical abnormality detectable on CT. It is extremely useful in determining the full extent of a malignant disease. Lymph nodes when small in size can commonly be missed or tend to appear normal on a routine CT scan, aiding in the detection of lymphatic metastasis.
What are the other uses of a PET CT scan?
PET scan is considered as the gold standard to demonstrate metabolic activity in the myocardium. This is particularly useful in patients after myocardial infarction/heart attack before subjecting them to revascularization procedures. A dead (non-viable) myocardium is not expected to improve in function even after restoration of the blood circulation by angioplasty or a bypass surgery. On the contrary, if the infarcted myocardium has preserved metabolism (viable-hibernating) it shows dramatic improvement in function. PET scans are also useful in various neurological conditions, especially dementias and epilepsy where various areas of the brain can be screened for abnormal metabolism.