The use of positron emission tomography (PET) for the detection and staging of cancer using [ 18 F]2-fluoro-2-deoxy-D-glucose ([ 18 F]FDG) demonstrates the power molecular imaging holds for targeting metabolic abnormalities in cancer . The overexpression of amino acid transporters in transformed cells is well recognized as a biomarker that can be targeted for diagnostic purposes, for example using radiolabeled non-natural amino acids. Such radiotracers offer advantages over [ 18 F]FDG when imaging tumors located adjacent to healthy tissues with naturally high glycolytic rates (e.g. the brain) or in cases where the cancer does not exhibit aberrant glucose uptake (e.g. prostate cancer) . (S)-4-(3-18 F-Fluoropropyl)-L-Glutamic Acid ([ 18 F]FSPG) is a radiolabeled non-natural amino acid used for PET imaging of system x C - .