Selectfluor, one of the most reactive and commonly used electrophilic fluorinating N–F reagents, has been radiolabeled with 18F. The resulting new [18F]‐labeled N–F reagent is safe, nontoxic, and easy to handle. The combined use of [18F]Selectfluor bis(triflate) and AgOTf allows for the preparation of electron‐rich 18F‐aromatic compounds through a simple “shake and mix” protocol at room temperature (see scheme; SA=specific activtiy).

[methyl-11C]choline (11C-choline) is a radioligand potentially useful for oncological positron emission tomography (PET). As a first step towards the development of a kinetic model for quantification of 11C-choline uptake, blood metabolism of 11C-choline during PET imaging was studied in humans. High-performance liquid chromatography (HPLC) and thin-layer chromatography (TLC) were used for the analysis of 11C-choline and its radioactive metabolites. Prior to human PET imaging we studied ex vivo the biodistribution and metabolism of intravenously administered 11C-choline in rats. Our results revealed that the radioactivity accumulated particularly in kidney, lung, adrenal gland and liver. Chromatographic analysis showed that the level of unmetabolized 11C-choline in rat plasma decreased from 42% +/- 20% (mean +/- SD) at 5 min to 21% +/- 10% at 15 min after injection. In accordance with these findings, in humans the unmetabolized 11C-choline represents 62% +/- 19% of the total radioactivity in arterial plasma at 5 min after injection and 27% +/- 12% at 15 min. In human venous plasma the corresponding values were 85% +/- 12% and 48% +/- 12% at 5 and 10 min, respectively. The major metabolite observed in both human and rat plasma was identified as 11C-betaine. In human arterial plasma this maximally represented 82% +/- 9% of the total radioactivity at 25 min after radiotracer injection. By 20 min after injection, the 11C-choline and 11C-betaine in human arterial plasma reached a plateau, and their fractional activities remained nearly constant thereafter. Although most of the circulating 11C-choline in blood is transported to tissues, it does not disappear totally from blood within the first 40 min after tracer injection.

The aim of this study was to evaluate 2-(2-nitro-1 H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl)-acetamide (EF5) labeled with 18 F-fluorine to image hypoxia in patients with squamous cell carcinoma of the head and neck (HNSCC). Methods: Fifteen patients with HNSCC were studied. Measurement of tumor blood flow was followed by an 18 F-EF5 PET/CT scan. On a separate day, 18 F-FDG PET/CT was performed to determine the metabolically active tumor volume. In 6 patients, dynamic 18 F-EF5 images of the head and neck area were acquired, followed by static images acquired at 1, 2, and 3 h after injection. In the remaining 9 patients, only static images were obtained. 18 F-EF5 uptake in tumors was compared with that in neck muscle, and the 18 F-EF5 findings were correlated with the 18 F-FDG PET/CT studies. Results: A total of 13 primary tumors and 5 lymph node metastases were evaluated for their uptake of 18 F-EF5. The median tumor-to-muscle 18 F-EF5 uptake ratio (T/M) increased over time and was 1.38 (range, 1.1-3.2) 3 h after tracer injection. The median blood flow in tumors was 36.7 mL/100 g/min (range, 23.3-78.6 mL/100 g/min). Voxel-by-voxel analysis of coregistered blood flow and 18 F-EF5 images revealed a distinct pattern, resulting in a T/M of 1.5 at 3 h to be chosen as a cutoff for clinically significant hypoxia. Fourteen of 18 tumors (78%) had subvolumes within the metabolically active tumor volumes with T/M greater than or equal to 1.5. Conclusion: On the basis of these data, the potential of 18 F-EF5 to detect hypoxia in HNSCC is encouraging. Further development of 18 F-EF5 for eventual targeting of antihypoxia therapies is warranted.

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Treatment of readily available α,α-difluoro- and α-fluoroarylacetic acids with Selectfluor under Ag(I) catalysis led to decarboxylative fluorination. This operationally simple reaction gave access to tri- and difluoromethylarenes applying a late-stage fluorination strategy. Translation to [(18)F]labeling is demonstrated using [(18)F]Selectfluor bis(triflate), a reagent affording [(18)F]tri- and [(18)F]difluoromethylarenes not within reach with [(18)F]F2.