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Last Updated: 12/22/16

Molecular and Nuclear Imaging (PET and SPECT)


PET Scan



PET scans may play a role in determining whether a mass is cancerous. However, PET scans are more accurate in detecting larger and more aggressive tumors than they are in locating tumors that are smaller than 8 mm a pinky nail (or half of a thumb nail) and/or less aggressive cancers. The size of smallest tumor mass that can be found at PET is constantly improving. 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 also commonly used to check if a treatment is working - if a tumor cells are dying and thus using less sugar.

PET scan
PET scans. Uptake of tracer in the lymph nodes involved with lymphoma in the groin, both axilla, and neck (red areas). Image coutesy of Dr. Jorge Carrasquillo, Nuclear Medicine Department, Clinical Center, National Institutes of Health.


Similar to PET, single photon emission computed tomography (SPECT) uses radioactive tracers and a scanner to record data that a computer constructs into two- or three-dimensional images. A small amount of a radioactive drug is injected into a vein and a scanner is used to make detailed images of areas inside the body where the radioactive material is taken up by the cells. SPECT can give information about blood flow to tissues and chemical reactions (metabolism) in the body.

In this procedure, antibodies (proteins that recognize and stick to tumor cells) can be linked to a radioactive substance. If a tumor is present, the antibodies will stick to it. Then a SPECT scan can be done to detect the radioactive substance and reveal where the tumor is located.

SPECT scan
SPECT scan. High levels of antibody in pelvis and axilla (red) and uptake in skin of the thigh and right shoulder (green) showing areas of cutaneous T-cell lymphoma. Image courtesy of Dr. Jorge Carrasquillo, Nuclear Medicine Department, Clinical Center.