Amyloid imaging in cognitively normal older adults: comparison between 18F-flutemetamol and 11C-Pittsburgh compound B

Purpose Preclinical, or asymptomatic, Alzheimer’s disease (AD) refers to the presence of positive AD biomarkers in the absence of cognitive deficits. This research concept is being applied to define target populations for clinical drug development. In a prospective community-recruited cohort of cognitively intact older adults, we compared two amyloid imaging markers within subjects: 18 F-flutemetamol and 11 C-Pittsburgh compound B (PIB). Methods In 32 community-recruited cognitively intact older adults aged between 65 and 80 years, we determined the concordance between binary classification based on 18 F-flutemetamol versus 11 C-PIB according to semiquantitative assessment (standardized uptake value ratio in composite cortical volume, SUVR comp ) and, alternatively, according to visual reads. We also determined the correlation between 18 F-flutemetamol and 11 C-PIB SUVR and evaluated how this was affected by the reference region chosen (cerebellar grey matter versus pons) and the use of partial volume correction (PVC) in this population. Results Binary classification based on semiquantitative assessment was concordant between 18 F-flutemetamol and 11 C-PIB in 94 % of cases. Concordance of blinded binary visual reads between tracers was 84 %. The Spearman correlation between 18 F-flutemetamol and 11 C-PIB SUVR comp with cerebellar grey matter as reference region was 0.84, with a slope of 0.98. Correlations in neocortical regions were significantly lower with the pons as reference region. PVC improved the correlation in striatum and medial temporal cortex. Conclusion For the definition of preclinical AD based on 18 F-flutemetamol, concordance with 11 C-PIB was highest using semiquantitative assessment with cerebellar grey matter as reference region.