Oral and IV Contrast Agents for the CT Portion of PET/CT

W5 the lesion and adjacent structures and CT enhancement characteristics such as phase and pattern. Most parenchymal organs and the lesions affecting them have similar attenuation values, which lie within a relatively narrow range, typically 30–80 HU. IV contrast material is used to increase the attenuation difference between normal and abnormal tissue. The result is increased lesion conspicuity, which is of particular importance in lesions in which FDG does not accumulate (Figs. 1–3). Furthermore, IV contrast enhancement can help differentiate benign from malignant lesions that have nonspecific FDG PET uptake. Similarly, IV contrast material may outline lesions within vascular structures (Figs. 1 and 4) and localize lesions that have increased FDG uptake but that would not be clearly seen on unenhanced CT images because of absence of a contour abnormality due to their size or would have similar attenuation to the surrounding structures (Fig. 5). The pyeloureteral system may not be well visualized at PET/CT because urinary excretion of FDG masks lesions. In addition, some renal lesions do not exhibit substantial FDG uptake (Fig. 6). Asymmetric FDG uptake should raise suspicion of transitional cell cancer, renal cancer, lymphoma, and ureteric obstruction or diverticulum. Asymmetric lack of uptake raises suspicion of renal cell cancer and renal cysts (Fig. 7).