PET/CT: Fundamental principles

Positron emission tomography (PET) facili- tates the evaluation of metabolic and molecular charac- teristics of a wide variety of cancers, but is limited in its ability to visualize anatomical structures. Computed to- mography (CT) facilitates the evaluation of anatomical structures of cancers, but can not visualize their meta- bolic and molecular aspects. Therefore, the combina- tion of PET and CT provides the ability to accurately register metabolic and molecular aspects of disease with anatomical findings, adding further information to the diagnosis and staging of tumors. The recent gen- eration of high performance PET/CT scanners com- bines a state of the art full-ring 3D PET scanner and a high-end 16-slice CT scanner. In PET/CT scanners, a CT examination is used for attenuation correction of PET images rather than standard transmission scan- ning using 68Ge sources. This reduces the examination time, but metallic objects and contrast agents that alter the CT image quality and quantitative measurements of standardized uptake values (SUV) may lead to artifacts in the PET images. Hybrid PET/CT imaging will be very important in oncological applications in the decades to come, and possibly for use in cancer screen- ing and cardiac imaging.