To Enhance or Not to Enhance?

In combined PET/CT imaging, functional data provided by 18FFDG increase diagnostic accuracy over conventional PET and CT in a variety of malignancies. The question to be raised is: how much is CT needed in PET/CT imaging? Discussion: In stand-alone CT imaging, contrast agents are applied to aid differentiation of anatomic structures, improve lesion localization, and support lesion characterization. Based on our experience, the most important benefit when applying CT contrast agents in PET/CT imaging relates to more precise anatomic localization of pathology by differentiation of the lesion from its surrounding structures on CT. This benefit must be considered most profound in the head and neck as well as the abdomen and pelvis, where delineation of pathology from muscles, vascular structures, or the intestine is critical. CT contrast agents can be of additional value in tumors with only mild or no increase in 18F-FDG uptake by supporting lesion detection and characterization. The complementary role of CT contrast agents and molecular contrast for PET/CT imaging is addressed in this review. The authors provide specific indications as to which contrast-enhanced CT data provide additional diagnostic value. Conclusion: Functional contrast aids lesion detection and characterization, whereas morphologic contrast improves lesion localization. CT contrast agents and PET tracers do not compete but rather are complementary in combined PET/CT imaging.