*2.3. Amino Acid Transporter-Targeting Probes*

Alternatives to [18F]FDG are a subject of interest. Occasionally, [18F]FDG may yield inexplicable images. The false-positive [18F]FDG uptake happens in Hashimoto's disease and Graves' disease. In addition, it is hard to find brain metastasis on [18F]FDG PET/CT images because of the intense background signals [57,58]. In recent years, amino acid probes have obtained incremental attraction as alternatives to [18F]FDG. Amino acids probes include [18F]fluoro-α-methyl tyrosine ([18F]FAMT), [18F]fluoro-dihydroxyphenylalanine ( [18F]FDOPA), L-[methyl-11C]-methionine ([11C]MET), [18F]fluoroethyl-tyrosine ([18F]FET), [ 18F]fluoroglutamine ([18F]FGln), and the newly discovered [18F]NKO-035. Of these, [ 18F]FDOPA, [11C]MET, and [18F]FGln have been investigated in TCs [59–63].
