The prediction would thus be that increased concentration of LAT1-relevant AMAs in plasma prior to [18F]FET injection would decrease [18F]FET uptake in the brain, as have been found in a single healthy subject [13] and in patients with phenylketonuria (PKU) [14] using l-[18F]fluorodopa, and in brain tumour patients studied with l-3-[123I]iodo-alpha-methyl-l-tyrosine ([123I]IMT) single photon emission tomography (SPECT) [15]. This evidence concerns the gene SLC7A5 and phenylketonuria.