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FIGURE 2. Paired PET imaging studies comparing 124I-FIAU and 18F-FHBG or 18F-FHPG were performed. Coronal (A) and axial (B) PET images are shown for 3 different rats. Each animal had 2 imaging studies within 24 h, and comparable image pairs are shown in each quadrant of A and B. Location of RG2TK+ xenograft is indicated by arrow. Linear scaling of image intensity was performed to achieve similar background intensity on all images; background radioactivity in thorax was 0.013 and 0.027 %dose/g for animal 1, 0.024 and 0.18 %dose/g for animal 2, and 0.23 and 0.24 %dose/g for animal 3 (FHBG or FHPG and FIAU, respectively). No radioactivity above background is visualized in control RG2 xenograft. Several tissues had substantially higher values than indicated on intensity scale. For example, FIAU levels in RG2TK+ xenografts in animals 1–3 were 0.55, 1.7, and 1.2 %dose/g, respectively. Also note high values of radioactivity in stomach (6.0 %dose/g) and bladder (3.9 %dose/g) in 2-h study (animal 2). FHBG levels in abdominal viscera (2.8–3.2 %dose/g) and bladder (11 and 80 %dose/g) were also substantial at 2 h (animals 1 and 2); similar values were measured for FHPG in abdomen (3.4 %dose/g) and bladder (63 %dose/g) of animal 3. Note that FIAU bladder radioactivity had essentially cleared by 24 h (animals 1 and 3).
