Clinical Applications of
PET & PET/CT
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.
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.
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.
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
the Effectiveness of Chemotherapy:
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.