Positron emission tomography versus positron emission tomography/computed tomography: from "unclear" to "new-clear" medicine.

PET/CT is a new diagnostic imaging modality, which proves that adding PET and CT is not merely additive, but highly synergistic. While PET provides high sensitivity for lesion detection, CT provides the anatomic backdrop, which frequently is important in order to make a specific diagnosis. CT can, however, also add sensitivity to PET, as certain lesions such as small clearly pathological lung nodules may not at all be visualized on PET alone; and PET clearly adds specificity to CT because, e.g., indeterminate lymph nodes seen on CT can often be diagnosed unequivocally as benign or malignant, using PET information. Furthermore, attenuation correction of PET data, which is needed for best PET image quality, can also be obtained using the same CT data. Hence, PET/CT also provides a very fast solution for obtaining attenuation images. The major clinical applications of PET/CT are in tumor imaging of the body and the search for inflammatory foci, while for brain imaging, PET/CT is less relevant. In the brain, post acquisition fusion of PET and MRI data is relatively easy, while post acquisition fusion of PET and CT or MR data in the body is unreliable and cumbersome. We strongly feel that PET/CT is the oncological staging "one-stop-shop" examination of the future for many tumors. The key question in the next few years will be how much CT is needed in PET/CT for which clinical question? The advent of ever faster CT scanners suggests that PET/CT eventually may also provide a tool for a cardiac "one-stop-shop." So the future of PET/CT indeed looks bright.