Test-retest reliability of central [C-11]raclopride binding at high D-2 receptor occupancy. A PET study in haloperidol-treated patients

Central D-2 dopamine receptor occupancy may be a useful measure to establish clinical guidelines for optimal antipsychotic drug treatment. The use of positron emission tomography (PET) to explore quantitative relationships among D-2 receptor occupancy and clinical effects depends on the reliability of such measurements. The calculation of D-2 receptor occupancy using [C-11]raclopride is routinely based on a ratio-equilibrium analysis, in which the ratio of radioactivity concentration in the striatum to that in the cerebellum is determined. To examine the reliability of such ratios, a test-retest analysis was performed in four schizophrenic patients treated with haloperidol decanoate. PET experiments with [C-11]raclopride were repeated in each subject during the same day. The putamen to cerebellum ratio (P/C ratio) ranged from 1.44 to 1.07 among the four patients, corresponding to a D, receptor occupancy of 62 to 71%. In each subject, the P/C ratios remained highly similar, with quotients 0.98, 1.01, 1.04 and 1.06 between the two experiments. The high test-retest reproducibility of the P/C ratios indicates that measurements of D-2 receptor occupancy with the present methods are highly reliable, and support the further use of PET to optimize the drug treatment of schizophrenia.