PURPOSE: To determine the reproducibility of measurements of brain 5-HT2A 
receptors with an [18F]altanserin PET bolus/infusion approach. Further, to 
estimate the sample size needed to detect regional differences between two 
groups and, finally, to evaluate how partial volume correction affects 
reproducibility and the required sample size.
METHODS: For assessment of the variability, six subjects were investigated with 
[18F]altanserin PET twice, at an interval of less than 2 weeks. The sample size 
required to detect a 20% difference was estimated from [18F]altanserin PET 
studies in 84 healthy subjects. Regions of interest were automatically 
delineated on co-registered MR and PET images.
RESULTS: In cortical brain regions with a high density of 5-HT2A receptors, the 
outcome parameter (binding potential, BP1) showed high reproducibility, with a 
median difference between the two group measurements of 6% (range 5-12%), 
whereas in regions with a low receptor density, BP1 reproducibility was lower, 
with a median difference of 17% (range 11-39%). Partial volume correction 
reduced the variability in the sample considerably. The sample size required to 
detect a 20% difference in brain regions with high receptor density is 
approximately 27, whereas for low receptor binding regions the required sample 
size is substantially higher.
CONCLUSION: This study demonstrates that [18F]altanserin PET with a 
bolus/infusion design has very low variability, particularly in larger brain 
regions with high 5-HT2A receptor density. Moreover, partial volume correction 
considerably reduces the sample size required to detect regional changes between 
groups.