Table 1. Assessment of Key Attributes during Imaging and Nonimaging Components of Radiotracer Development.

radiotracer attribute	nonimaging assessment	imaging assessment
binding affinity	potency in in vitro assays	binding potential (Bmax/Kd, smaller Kd = larger BP)
binding kinetics	vary preincubation and washing steps in in vitro assays, autoradiography	qualitative TAC analysis
		quantitative kinetic modeling
BBB penetration	mass spectrometry of unlabeled tracer	%ID/cc in brain
	in silico prediction
specific binding	“no wash” autoradiography	homologous blocking
	in silico prediction	knockout animals
selective binding	autoradiography	heterologous blocking
	systematic screening (PDSP)	knockout animals