What is PET/CT Used For?

PET/CT is a combination of Positron Emission Tomography (PET) and Computed Tomography (CT). This is currently one of the most effective tools radiologists (doctors who read x-rays) use to detect the presence and stage of cancers. PET/CT imaging helps radiologists detect cancer, evaluate the amount and spread of disease and detect any recurrent tumors. This information is then relayed to the oncologist (a doctor who treats cancer), who is better able to select the most appropriate treatments and determine if the therapy is working.

How is it Done?

The test involves injecting a very small dose of a radioactive sugar, called a radiotracer, into the vein of the patient’s arm. The sugar travels through the body and is absorbed by tissues, such as cancer, that are very active. Very active tissue requires large amounts of sugar for energy. Next, the patient will be asked to lie down on a flat examination table that is moved into the center of a PET/CT scanner, which is a doughnut-like shaped machine. Information regarding the location of abnormal levels of radioactive sugar obtained from the whole-body PET/CT scan helps the radiologist effectively pinpoint the source of cancer and detect whether cancer is isolated to one specific area, or has spread to other organs.

How the Results are Used

From this information oncologists can plan an effective treatment strategy. Treatment options include surgery, radiation therapy, systemic therapy, or a combination therapy, where one or more of these options are combined.

During the course of treatment of certain cancers, obtaining a second PET/CT scan may allow physicians to monitor the effectiveness of the current cancer therapy and provide the oncologist with the opportunity to change the treatment strategy if it is not working, avoiding the cost and side effects of ineffective therapeutic procedures.

After completing the treatment regimen, a follow-up whole-body PET/CT scan can provide information to assess if the treatment was successful, and if areas that were previously abnormally active have responded. Often, scar tissue at the site of surgical resection or radiation treatment may appear as an abnormality on the CT scan. The PET portion of the PET/CT scan can detect residual disease within the scar tissue and indicate if the treatment was successful, or if the tumor has returned.

Other Uses of PET/CT

PET/CT currently has two other common usages. The first involves assessing the heart muscle for activity when the surgeon is unsure whether a bypass will potentially save heart tissue, or if the heart tissue is dead and has turned to scar. Heart tissue that is just stunned from lack of oxygen will continue to show activity and this tissue is salvageable with a bypass.

The second use is to evaluate brain abnormalities, such as tumors, memory disorders, seizures and other central nervous system disorders. The pattern of activity can often help the neurologist determine the site of a seizure, or the type of dementia the patient may be suffering from.

B: Scott Steffen, MD, Staff Radiologist with Triad Radiology Associates