Regional brain uptake and striatum/organ ratio of (-)-[18F]18a in male SD rats. Both figures showed the radioactivity retention was the highest in the striatum at 30, 60 and 120 min p.i., while the radioactivity was quickly washed out in other brain regions. CBL: cerebellum; STR, striatum; BSTM, brain stem; CTX, cortex; THA, thalamus.