Few 18F PET radioligands have been developed and evaluated for imaging of the A1R as shown in Figure 3. Of these, [18F]CPFPX has shown high affinity and selectivity for A1R6,92; however, due to the high in vivo metabolism, this radiotracer exhibited a short biological half-life of only about 10 minutes.84 Despite this fact, [18F]CPFPX has been used for imaging of A1Rs in the human brain93 and is currently a standard PET radioligand for evaluation of the A1R density in CNS disorders such as sleep–wake research.84,94-96
