Comparison of ¹⁸F-FDG, ¹⁸F-FET and ¹⁸F-FLT for differentiation between tumor and inflammation in rats

Introduction: The goal of this study was to compare the glucose analog, 2-[¹⁸F]fluoro-2-deoxy-d-glucose ([¹⁸F]-FDG), the amino acid analog, o-(2-[¹⁸F]fluoroethyl)-l-tyrosine ([¹⁸F]-FET) and nucleoside analog, 3′-[¹⁸F]fluoro-3′-deoxythymidine ([¹⁸F]-FLT) with regard to their feasibility for differentiating tumors from inflammation. Methods: In Fisher rat models bearing both 9L tumor and inflammation, the biodistributions and positron emission tomography (PET) images of [¹⁸F]-FDG, [¹⁸F]-FET and [¹⁸F]-FLT at 60 min post injection were compared. Pretreatment with thymidine phosphorylase before injection of [¹⁸F]-FLT was performed. Results: The tumor-to-blood (T/B) and tumor-to-muscle (T/M) ratios of [¹⁸F]-FDG were significantly higher than those of [¹⁸F]-FET and [¹⁸F]-FLT (P<.01); however, the accumulation of [¹⁸F]-FDG [1.23±0.52 percent injected dose per gram of tissue (%ID/g)] in inflammation was also elevated. T/B and T/M ratios of [¹⁸F]-FET (2.3±0.5 and 2.2±0.5) were higher than those of [¹⁸F]-FLT (1.6±0.6 and 1.6±0.5), and inflammation uptake of those tracers was very low (0.63±0.19 and 0.27±0.16 %ID/g, respectively). [¹⁸F]-FET and [¹⁸F]-FLT showed higher selectivity indices (tumor-to-inflammation ratio corrected background) than [¹⁸F]-FDG. In PET images, [¹⁸F]-FDG was found to be accumulated in both tumor and inflammation, but [¹⁸F]-FET and [¹⁸F]-FLT selectively localized in tumor. Conclusion: Our data confirm the result of previous studies that [¹⁸F]-FET and [¹⁸F]-FLT are superior to [¹⁸F]-FDG in differentiating tumor from inflammation.