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Clinical Applications of PET & PET/CT

Oncology Overview of PET/CT Fusion Technology:

A PET/CT scan combines PET and CT into one unit. PET utilizes fluorodeoxyglucose (FDG), a glucose analog labeled with radioactive fluorine, to visualize processes within the body. This glucose tracer emits positrons, or positive electrons. As the positrons encounter electrons within the body, a reaction occurs, which produces paired gamma rays that travel in opposite directions. These gamma rays are then detected by the PET scanner, which positions the FDG spatially within the patient's body. The images produced by the PET portion of the fusion scanner contain information about the body's utilization of glucose. Malignant or cancerous tumors utilize more glucose than most other tissues leading to the detection of malignancy and specific tumor sites, PET is therefore a unique imaging modality in its ability to metabolically characterize biologic tissues according to their utilization of glucose and their likely malignant nature. CT uses x-rays to make cross-sectional images (called slices) of your body. The structure of body organs is more clearly visualized with CT than with conventional x-rays. The fusion scanner combines the anatomical information obtained from CT with the biological PET information to form an image that records living tissues and life processes with great precision and detail.

Clinical Applications in Oncology:

Early Detection: PET can detect cancers in their earliest stages. Since a PET scan images the metabolic activity of the body's tissues, it can often show tumor pathology before anatomical or structural changes are evident on conventional imaging. Also, when an x-ray, MRI or CT shows a lesion, it may not accurately characterize whether it is benign or malignant. PET can often make this determination, thereby sometimes avoiding surgical biopsy when the PET scan is negative (which would indicate that the lesion is benign). Conversely, in certain cases when a PET scan is positive for cancer that has already spread (metastasized) to other organs, a surgical cure is not possible and chemotherapy may be recommended. PET allows for far greater accuracy in the diagnosis and staging of many types of cancer. In cancers where surgery is the best course of action, the PET/CT fusion scanners provide surgeons with the ability to not only differentiate between benign and malignant tumors, but it shows them exactly where the tumors are located, thereby allowing for more targeted and often shorter surgeries, which may decrease patient morbidity.

Staging of the Disease:

As an essential tool in the development of cancer treatment plans, PET/CT scanners are extremely sensitive in determining the full extent of the malignant disease. Since a PET/CT scan can image the whole body, the presence, location and extent of distant metastases can be determined much more accurately than by any other diagnostic test. This allows the physician and patient to more appropriately decide the most appropriate therapeutic course. In about one- third of patients, staging of their malignancy is changed following a PET scan and, therefore, treatment plans are altered.

Checking for Recurrence:

Cancer recurrence is unfortunately quite common in many types of cancers. The PET component of the scanner has the ability to differentiate between tumor recurrences and the changes caused by the patient's cancer treatment. PET is the most accurate imaging procedure capable of making this differentiation. The benefit is that recurrence can be detected earlier and more accurately without invasive procedures.

Assessing the Effectiveness of Chemotherapy:

Research indicates that PET/CT fusion technology is playing an increasingly important role in assessing the effectiveness of chemotherapy by evaluating early response to a selected drug combination. The level of tumor metabolism and tumor size are compared on PET/CT scans taken before and after chemotherapy. A successful response to administered tumor drugs, seen as a significant decrease in a tumor's glucose metabolism, can often be observed on a PET/CT scan before a tumor shrinks in size.

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