Comparison of in vivo [18F]FAZA- and [18F]FDG images and pimonidazole immunohistochemistry of the same tumor. A and C, Typical sample of [18F]FDG- and [18F]FAZA-PET images of a CT26 colon carcinoma (tumor size category: 0.15-0.5 cm3). B, ex vivo analysis of the same CT26 colon carcinoma (A and C) by H&E staining of tumor slices. Red squares in A and C indicate the H&E-stained tumor region. D and E, ex vivo pimonidazole immunohistochemistry of the areas indicated in A and C. The mice were injected with 60 mg/kg pimonidazole 1 h prior to ex vivo analysis. Tumor slices were analyzed using the Hypoxyprobe™-1 kit for the detection of tissue hypoxia. Control staining was performed with PBS instead of the primary antibody.