PET - Positron Emission Tomography

The positron emission tomography (PET) scan creates two- or three-dimensional computerized images of chemical changes, such as sugar metabolism, that take place in tissue. Typically, the patient is given an injection of a substance that consists of a combination of a sugar and a small amount of radioactively labeled sugar. The National Cancer Institute (NCI) says PET scans are used most often to detect cancer (Read about "Cancer: What It Is") and to monitor how effective treatment is. (Read about "Cancer Treatments") The radioactive sugar can help in locating a tumor, because cancer cells take up or absorb sugar more avidly than other tissues in the body. If a tumor is present, the radioactive sugar will accumulate in the tumor.

Though PET scans are mainly used for cancer, they can also help with other conditions. They can help in ascertaining the damage to the heart after a heart attack. (Read about "Heart Attack") They also help with brain disorders (Read about "The Brain") including some seizure disorders (Read about "Seizures") and some memory problems. (Read about "Dementia")

After receiving the radioactive sugar, the patient lies still for about 60 minutes while the radioactively labeled sugar circulates throughout the body. The patient then lies on a table, which gradually moves through the PET scanner six to seven times during a 45-60-minute period. Sensors in the PET scanner detect the radioactivity as the compound accumulates in different regions. A computer uses the data gathered by the sensors to construct multicolored two- or three-dimensional images that show where the compound acts. Using different compounds, PET can show blood flow, oxygen and glucose metabolism, and drug concentrations in the tissues. A computer translates this information into the images that are interpreted by a radiologist.

PET scans may play a role in determining whether a mass is cancerous. However, NCI says PET scans are more accurate in detecting larger and more aggressive tumors than they are in locating tumors that are smaller than 8 mm and/or less aggressive. They may also detect cancer when other imaging techniques show normal results. PET scans may be helpful in evaluating and staging recurrent disease (cancer that has come back). PET scans are beginning to be used to check if a treatment is working - if tumor cells are dying and thus using less sugar.

PET/CT Scan

Combined PET/CT scanning joins two imaging tests, CT and positron emission tomography (PET), into one procedure. A PET scan creates colored pictures of chemical changes (metabolic activity) in tissues, while a CT scan obtains cross-sectional pictures of the body. (Read about "CT Scan - Computerized Tomography") Because cancerous tumors usually are more active than normal tissue, they appear different on a PET scan.

Though PET/CT scans are mainly used for cancer they can also help with other conditions. They can help in ascertaining the damage to the heart after a heart attack. (Read about "Heart Attack") They also help with brain disorders (Read about "The Brain")including some seizure (Read about "Seizures") disorders and some memory problems. (Read about "Dementia")

Combining CT with PET scanning may provide a more complete picture of a tumor's location and growth or spread than either test alone. The combined PET/CT scan may also reduce the number of additional imaging tests and other procedures a patient needs.