In spite of a large number of folate-based nuclear imaging agents which have been developed in the last two decades only one SPECT radiotracer (99mTc-EC20, EtarfolatideTM) is currently being used in clinical trials in the U.S. for SPECT imaging. For over a decade investigators have been focusing research activities on the development of a 18F-based folate radiotracer for PET imaging (13-16). Recently, a novel folate radiotracer has been developed, 3'-aza-3-[18F]fluorofolic acid (herein referred to as [18F]-AzaFol), for PET imaging purposes.