Figure 4a. Differential uptake of FDG. Axial fused FDG PET-CT images of patients with supraglottic squamous cell carcinoma (a) and colon cancer (b) show metastases to a left supraclavicular lymph node (a) and to the liver (b). The metastases demonstrate differential FDG uptake in proportion to their metabolic activity. The necrotic centers of the metastases (straight solid arrow) show negligible uptake compared with their hypermetabolic peripheries (open arrows). Arrowheads in b = physiologic FDG activity in the left kidney, wavy arrow in b = simple hepatic cyst without metabolic activity.