Straightforward radiosynthesis protocols for F-labeled radiopharmaceuticals are an indispensable but often overlooked prerequisite to successfully perform molecular imaging studies in vivo by PET. In recent years, thanks to the expansion of theF chemical toolbox, structurally diverse and novel clinically relevant radiopharmaceuticals have been synthesized with both high efficiency and ready implementation. This article provides an overview of recent F-labeling methodologies, specifically for B-F, Si-F, Al-F, and iodine (III)-mediated radiofluorination via the spirocyclic iodonium ylide technology.

The physical and biological properties of a water-soluble polymeric contrast agent based on a complex of N-(2-hydroxypropyl)methacrylamide copolymer with gadolinium (HE-24.8) were investigated, and its potential for experimental magnetic resonance (MR) angiography was assessed. Relaxivities of Gd-DTPA-BMA, Gd-DTPA-HSA (human serum albumin), and HE-24.8 were determined at 1.5 T. Thermic stability and biocompatibility of HE-24.8 were assessed in vitro and by analyzing kinetics and organ distribution in rats for up to 2 weeks. For comparison, HE-24.8- and Gd-DTPA-HSA-enhanced micro-MR angiographies of brain, chest, and subcutaneous tumors in rats were performed. T1 relaxivity of HE-24.8 (21.3 +/- 1.1 mM(-1) s(-1)) was 5-fold higher than that of Gd-DTPA-BMA (4.1 +/- 0.1 mM(-1) s(-1)) and twice as high as that of Gd-DTPA-HSA (12.4 +/- 0.2 mM(-1) s(-1)). Varying the molecular weight of the polymer (15-46 kDa) did not significantly change the T1 relaxivity. In rats, 20 and 10% of the injected dose of HE-24.8 was detected at 24 and 168 h postinjection, respectively. Upon a relatively rapid initial renal clearance, no specific retention in any organ was noted, with some exception for the reticulo-endothelial system. No measurable release of gadolinium from the polymer-Gd complex or cell toxicity was observed during its incubation in aqueous environment. Excellent display of rat and tumor vascularization was achieved with Gd-DTPA-HSA and HE-24.8; however, contrast of vessels was higher in HE-24.8-enhanced scans. HE-24.8 is considered a macromolecular contrast agent highly suited for experimental MR studies.