. Comparison of cerebral metabolism using the PALZ tool in clinically unimpaired elderly and MCI subjects with and without amyloid deposition. Human Amyloid Imaging 2011 Meeting Abstracts. 2011 Jan 15;

Abstract:

Background: Lowered cerebral metabolism, using [18F]fluoro-2-deoxy-D-glucose (FDG), has long been associated with AD pathogenesis. One method for identification of gAD-likeh FDG scans is the PALZ tool. Using Pittsburgh Compound-B (PiB), several have reported ~25% of clinically unimpaired, elderly controls (NC) and ~60% of Mild Cognitive Impairment (MCI) subjects display increased PiB. The present studies compared cerebral metabolism in MCI and NC with and without amyloid deposition.

Methods: Subjects underwent PiB and FDG PET imaging. Tissue ratios were calculated for cortical regionsof- interest (ROI) and normalized to cerebellum (SUVR). The FDG PET data were analyzed using the PALZ tool, which implements automatic Alzheimer discrimination methods developed by Herholz et al. A t-sum >11,090 is considered AD-like, but values over 6,000 may be associated with more subtle abnormalities.

Results: Among both MCI and NC subjects, those identified as PiB(+) at baseline displayed significantly higher (i.e. more abnormal) PALZ score (p 6,000). Of the 16 PiB(-) MCI, 1 had an AD-like PALZ score and 4 had an elevated PALZ score (>6,000). Of 75 NC, 21 were PiB(+), of these, 4 had an AD-like PALZ score and 4 had an elevated PALZ score (>6,000). Of the 54 PiB(-) NC, 2 had an AD-like PALZ score and all others had PALZ scores under 6,000. A Fisher exact test revealed in both MCI and NC a significant difference between the proportion of PiB(+) and PiB(-) with abnormal PALZ scores (p>0.05).

Conclusions: Among both MCI and NC subjects, it appears that increased PiB is associated with cortical hypometabolism, measured by PALZ. It will be of great interest to follow the four categories of subjects: PiB(+)/ PALZ(+), PiB(-)/PALZ(-), PiB(+)/PALZ(-) and PiB(-)/PALZ(+) to determine the eventual clinical outcome.

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