Radiology Rounds - May 2004 - PET/CT for Tumor Imaging

PET imaging using the glucose analog 18F-FDG as a tracer is an excellent method to detect small focal sites of high metabolic activity, which are frequently indicative of tumors. However, it is very difficult to identify the anatomic location of these focal sites precisely with PET alone. The only anatomic markers in FDG-PET are organs, such as the heart, that are known to have high metabolic rate, and the excretory system. In addition, the spatial resolution of PET is about 5-6 mm, much lower than that of other imaging methods, such as CT. These limitations make it difficult to make an accurate interpretation of the anatomic location of the focal site of tracer uptake, especially in regions of the body where anatomy is complex, such as the neck and the abdomen. Therefore, patients often receive both PET and CT scans. Computer programs are used to co-register the scans and thus the anatomic information from CT is combined with the physiologic information from PET.