General Information about PET/CT
PET/CT in Types of Cancer
PET/CT in Heart and Brain Disease
What Is PET
Positron Emission Tomography (PET) is rapidly becoming 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. Studies demonstrate that PET
offers significant advantages over other forms of imaging such as CT or MRI
scans in diagnosing disease. Last year more than 200,000 PET scans were performed
at more than 700 sites around the country. If you're interested in learning
how a PET scan can benefit you and need additional information, talk with your
local health care provider or referring physician. At the end of this page are
links to other sites with PET information too.
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, and 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.
Cancer & PET
Normal body cells grow, divide, and die in an orderly fashion replacing worn-out
or dying cells and repairing injuries. Sometimes these normal cells begin to
grow uncontrollably. These abnormal cells outlive the bodies normal cells and
continue to grow and divide forming new abnormal cells. The mass of extra cells
forms a growth or tumor, which can be benign or malignant. They are not cancerous.
Benign tumors can be removed low probability of recurrence and are usually not
life threateing. But if the tumor is malignant it is cancerous. In a process
called metastasis, cells from a malignant tumor can break off and travel to
other parts of the body via the bloodstream or lymphatic system where they begin
to grow and replace normal tissue. Cells from a malignant breast tumor can spread
to another organ, for example the brain. Although these cells are in the brain,
the cancer is still breast cancer.
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.
How Can PET/CT Make a Difference?
- 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. PET shows whether or not a tumor is benign or malignant.
No other imaging technique can do this! Reports in the scientific literature
find that PET correctly identifies detected lesions 97% of the time. Painful,
invasive surgery, such as thoracotomy, may no longer be necessary for diagnosis.
PET shows the extent of disease -- called staging -- of lung cancer, colorectal
cancer, melanoma, head and neck cancer, breast cancer, lymphoma and many other
cancers. For patients whose cancer is newly diagnosed, it is important to
determine if the cancer has spread to other parts of the body, so that appropriate
treatment can be started. PET can search the entire body for cancer in a single
examination, called a "whole body scan", revealing any metastases
as well as the primary site.
- 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 and CT or MRI
Because PET measures metabolism, as opposed to MRI or CT, which "see"
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 an MRI or CT scan through "fusion"
to give a full three-dimensional view of an organ and the location of cancer
within that organ. Newer PET scanners are being made that are a combination
of PET/CT devices.
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