PET analysis of central [11 C]raclopride binding in healthy young adults and schizophrenic patients—reliability and age effects

Central D2‐dopamine receptor occupancy determined by positron emission tomography (PET) during neuroleptic drug treatment may be a useful measure for optimal dose finding in schizophrenic patients. The clinical benefit is dependent on the reliability of such determinations. The ratio of radioactivity in the striatum to that of the cerebellum is widely used for calculation of D2‐receptor occupancy and as an index of D2‐dopamine receptor density. To test the reliability of such ratios a test‐retest analysis was performed in a series of healthy subjects. The reliability was very high, both when experiments were repeated on the same day and after time intervals of months to years. A group of subjects were examined twice using PET camera systems with different resolution. The striatum to cerebellum ratios obtained from the high‐resolution PET camera system were significantly higher than ratios from the camera with lower resolution. The age effect on the striatum to cerebellum ratio was examined in 25 healthy young adults and in 18 neuroleptic‐naive schizophrenic patients. A statistically significant decline was found both in the healthy controls and in the schizophrenic patients. The results do not support the view that there is a lack of age effect on the D2‐dopamine receptor density in schizophrenia.