MRI Scans Acquisition and Quantification

MRI scans were obtained with a 3T scanner (Ingenia CX, Philips, the Netherlands) at the neuroimaging unit at Barcelonaβeta Brain Research Center. The MRI protocol was identical for all participants and included a high-resolution 3-dimensional T1-weighted turbo field echo sequence (voxel size 0.75 × 0.75 × 0.75 mm³, repetition time/echo time 9.90/4.6 milliseconds, flip angle 8°).

T1-weighted images were automatically segmented, and cortical thickness was measured in the regions from the Desikan-Killiany cortical atlas using FreeSurfer version 6.0.³⁵ Segmentation results were visually quality controlled by an expert. The cortical AD signature was then estimated for each participant from the thickness of the following areas: entorhinal, inferior temporal, middle temporal, and fusiform. The signature was calculated as the mean thickness across these regions weighted by their surface area, as previously proposed.^36,37 Cortical thickness was calculated for the whole signature and for all the individual regions.