Comparison of MRI based and PET template based approaches in the quantitative analysis of amyloid imaging with PIB-PET

Rationale: [11C]Pittsburgh compound-B (PIB) has been the most widely used positron emission tomography (PET) imaging agent for brain amyloid. Several longitudinal studies evaluating the progression of Alzheimer's disease (AD), and numerous therapeutic intervention studies are underway using [11C]PIB PET as an AD biomarker. Quantitative analysis of [11C]PIB data requires the definition of regional volumes of interest. This investigation systematically compared two data analysis routes both using a probabilistic brain atlas with 11 bilateral regions. Route 1 used individually segmented structural magnetic resonance images (MRI) for each subject while Route 2 used a standardised [11C]PIB PET template. Methods: A total of 54 subjects, 20 with probable Alzheimer's disease (AD), 14 with amnestic Mild Cognitive Impairment (MCI) and 20 age-matched healthy controls, were scanned at two imaging centres either in London (UK) or in Turku (Finland). For all subjects structural volumetric MRI and [11C]PIB PET scans were acquired. Target-to-cerebellum ratios 40min to 60min post injection were used as outcome measures. Regional read outs for grey matter target regions were generated for both routes. Based on a composite neocortical, frontal, posterior cingulate, combined posterior cingulate and frontal cortical regions, scans were categorised into either 'PIB negative' (PIB-) or 'PIB positive' (PIB+) using previously reported cut-off target-to-cerebellar ratios of 1.41, 1.5 and 1.6, respectively. Results: Target-to-cerebellum ratios were greater when defined with a [11C]PIB PET template than with individual MRIs for all cortical regions regardless of diagnosis. This difference was highly significant for controls (p