[Principles of PET/CT and clinical application]

Medicine today imposes high demands on diagnosing disease. Techniques should be preferably noninvasive, identify the disease at an early stage, and be quick and accurate. Frequently, these demands can only be met by employing various diagnostic modalities. Consequently, the integration of two imaging modalities, such as the combination of PET and CT, increases the quality of coregistration and facilitates a timely diagnosis. However, complex imaging procedures require a judicious choice of the areas of application. If, for example, both PET and CT are indicated then a combined PET/CT exam results in improved diagnosis, whereby the actual benefit will depend upon the clinical problem. Typically we expect an advantage of 10% with PET/CT compared to separate examinations with CT and PET. In addition, PET/CT allows for new indications and applications, which cannot be performed satisfactorily with independent examinations and retrospective image alignment. One example is the application of PET/CT in radiation therapy planning.