PURPOSE: The serotonin 2A (5-HT(2A)) receptor is of interest in several 
psychiatric and neurological diseases. In the present study we investigated the 
longitudinal stability of 5-HT(2A) receptors and the stability of the 
quantification procedure in the elderly in order to be able to study elderly 
patients with neuropsychiatric diseases on a longitudinal basis.
METHODS: [(18)F]-Altanserin PET was used to quantify 5-HT(2A) receptors in 12 
healthy elderly individuals at baseline and at 2 years in six volumes of 
interest. A bolus/infusion protocol was used to achieve the binding potential, 
BP(P). The reproducibility as assessed in terms of variability and the 
reliability as assessed in terms of intraclass correlation coefficient (ICC) 
were used to compare inter- and intraobserver stability and to evaluate the 
effects of increasing complexity of partial volume (PV) corrections. We also 
compared the stability of our measurements over 2 years with the stability of 
data from an earlier study with 2-week test-retest measurements.
RESULTS: BP(P) was unaltered at follow-up without the use of PV correction and 
when applying two-tissue PV correction, test-retest reproducibility was 12-15% 
and reliability 0.45-0.67 in the large bilateral regions such as the parietal, 
temporal, occipital and frontal cortices, while orbitofrontal and anterior 
cingulate cortical regions were less stable. The use of PV correction decreased 
the variability but also decreased the between-subject variation, thereby 
worsening the reliability.
CONCLUSION: In healthy elderly individuals, brain 5-HT(2A) receptor binding 
remains stable over 2 years, and acceptable reproducibility and reliability in 
larger regions and high intra- and interobserver stability allow the use of 
[(18)F]-altanserin in longitudinal studies of patients with neuropsychiatric 
disorders.