Time-activity curve (A) and associated blood plasma nicotine concentration (B) from representative subject. (A) Equilibrium was reached before subject had smoked to satiety: for this subject, average percentage change was 3.1%/h in thalamus, 3.9%/h in striatum, 0.1%/h in mean cortex, and 2.7%/h in cerebellum. Two to 5 h after smoker had smoked to satiety, there appeared to be little change in kBq/cm3, suggesting that pseudoequilibrium state was achieved. (B) Highest nicotine concentration was observed at 20 min after initiation of tobacco smoking.