Computational protocol: FDG PET and MRI in Logopenic Primary Progressive Aphasia versus Dementia of the Alzheimer’s Type

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Protocol publication

[…] Voxel-level comparisons were performed for both MPRAGE and FDG-PET using SPM5 . All MPRAGE scans were spatially normalized to a customized template and segmented into gray matter (GM), white matter (WM) and cerebrospinal fluid using the unified segmentation model , followed by the hidden Markov random field clean up step . All GM images were modulated and smoothed with an 8 mm full width-at-half maximum (FWHM) smoothing kernel. FDG uptake images were co-registered to the subject’s MPRAGE using 6 degrees-of-freedom registration. An in-house modified version of the automated anatomical labeling (AAL) atlas, containing pons, was propagated to native MPRAGE space and all voxels in the FDG-PET image were divided by median uptake of the pons to form FDG uptake ratio images. Native space GM and WM segmentations were then combined to form a brain tissue probability mask. The masks were re-sampled to the resolution of the PET images, smoothed at 6 mm FWHM, and used to perform a 2-compartment partial volume correction (PVC) on the FDG uptake ratio images. Both the non-PVC corrected and the PVC corrected images were analyzed. The FDG images were then normalized to the customized template using the normalization parameters from the MPRAGE normalization and smoothed at 8 mm FWHM.Voxel-level comparisons were performed between lvPPA and controls, DAT and controls, and lvPPA and DAT, using two-sided T-tests in SPM5. Differences between disease groups and controls were assessed at p<0.0005, after correction for multiple comparisons using the false discovery rate (FDR) correction, with an extent threshold of 100 voxels. Differences between lvPPA and DAT were assessed uncorrected for multiple comparisons at p<0.001 with an extent threshold of 100 voxels. Age and gender were included in all analyses as covariates, with total intracranial volume (TIV) included as an additional covariate in the GM comparisons, and time from onset to scan (disease duration) included as a covariate in the comparisons between lvPPA and DAT. Total intracranial volume was measured in SPM5 by propagating a template-drawn TIV mask to subject space, and then performing an erosion step to remove border voxels. […]

Pipeline specifications

Software tools SPM, AAL
Application Magnetic resonance imaging
Diseases Alzheimer Disease, Brain Diseases, Dementia, Epilepsy, Temporal Lobe