Table 1.

Properties required for PET tracers.

Properties	Requirements
High blood–brain barrier permeability	>4%ID/g at 2 min post injection in normal mice
Rapid clearance	2–30 min brain uptake ratio in mice > 10
High binding affinity	Kd or Ki < 20 nM for target(s)
Off-target binding	None
Reversible binding to target	Reversible binding to target(s)
Stability	No radiolabeled metabolites in the brain