The impact of different 18FDG PET healthy subject scans for comparison with single patient in SPM analysis.

Background: Statistical Parametric Mapping (SPM) has been applied for single-subject evaluation of [18F]FDG uptake in Alzheimer Disease (AD). In a single-subject framework, the patient is compared to a dataset of [18F]FDG PET images from healthy subjects (HS) evaluating brain metabolic abnormalities. No studies exist that assess the effects on SPM analysis of HS [18F]FDG PET datasets acquired from different subjects and using different PET scanners including the same or different PET scanners than those used for patients. This work aims to elucidate this issue from a methodological perspective.

Methods: We considered six different [18F]FDG PET datasets, from different HS populations, acquired by different PET scanners. We applied SPM5 procedures for single-subject comparison with each of the six HS datasets in 10 probable AD patients showing the typical [18F]FDG pattern. We also implemented the same comparison in 3 probable AD patients and in 7 patients with a clinical diagnosis of Mild Cognitive Impariment (MCI), showing subtle changes on visual inspection of [18F]FDG distribution.

Results: Considering the 10 patients with the typical [18F]FDG pattern, the results were comparable for all the SPM maps. In the 3 probable AD patients with subtle changes in [18F]FDG distribution, no significant AD pattern emerged when a small number (<20) of HS was used, whereas a significant AD pattern appeared when a large (>50) HS image set was used. In the 7 considered MCI patients the use of a large (>50) HS image set allowed to assess significant hypometabolic patterns related to a probable neurodegenerative pathology.

Conclusions: The use of large HS datasets of PET scans (>50) is recommended for single-subject SPM analysis. On condition that appropriate preprocessing steps are provided, large HS datasets can include HS images acquired with different PET systems, not including images from the same scanner of that used for patients.