3t system

PCA patients, as well as a group of 30 age- and gender-matched healthy subjects (CTRL, men/women: 14/16; mean age = 61.5; standard deviation = 8.4; age range = 45–79), underwent the MRI protocol. Brain MRI were acquired with a 3 T system (Siemens, Erlangen, Germany) at the Center for Magnetic Resonance Research (CENIR), Brain and Spine Institute (ICM), Paris. A high-resolution structural volume was acquired using a T1-weighted 3D magnetization prepared rapid gradient echo (MPRAGE) sequence (160 sagittal images; thickness 1 mm; FOV 256 × 256 mm²; matrix size 256 × 256). Eight PCA patients (two PCA-tAD, four PCA-aAD and two PCA-nonAD) were scanned with compatible parameters but on a different MRI machine. The type of MRI machine was therefore added as a control covariate in our statistical analyses.

Brain MRI scans were acquired with a 3T system (Siemens, Erlangen, Germany) at the Center for Magnetic Resonance Research (CENIR), Brain and Spine Institute (ICM), Paris. A high-resolution structural volume was acquired using a T1-weighted 3D magnetization prepared rapid gradient echo (MP-RAGE) sequence (160 sagittal images; thickness 1 mm; field of view 256×256 mm²; matrix size 256×256). The functional images were acquired at rest by T2*-weighted fast echo planar imaging (flip angle = 90◦, echo time = 30 ms, repetition time = 2.26 s, 45 interleaved axial slices, gap = 0.3 mm, voxel size = 3 × 3 × 3 mm³, acquisition time=8 min=). During RS fMRI scanning, subjects were instructed to remain motionless, to keep their eyes closed, and to not think about anything in particular. Fat saturation was performed to avoid chemical shift artifacts. All slices were positioned to run parallel to a line that joins the most inferoanterior and inferoposterior parts of the corpus callosum.

All MR imaging were performed on the 3T system (Siemens, Erlangen, Germany). All participants underwent structural T-1 weighted, axial fluid attenuation inversion recovery (FLAIR), and susceptibility weighted imaging. FLAIR images were acquired with TR (repetition time) =9000ms, TE (echo time) =99 ms and TI (inversion time) =2500 ms; FA (flip angle) 130^O, slice thickness: 3.3 mm, FOV (field of view) 220 mm, matrix=256x192 reconstructed as 30 256×256 images (See Figure 1).Figure 1

Examples of different severity of white matter lesions in study subjects. (A) None (65 year old European American female). (B) Thought present (66 year old African American male). (C) Pronounced (70 year old European American female).

WMH was graded from 0 to 3 on the Fazekas scale.22 (link) Periventricular (PWMH) and deep white matter hyperintensities (DWMH) were graded separately and summed to create the total load (possible score 0–6). Severe WMH was defined as a total (summed) score ≥4. We analyzed and calculated the following imaging markers:

Any DWMH (Fazekas 1–3), Any PWMH (Fazekas 1–3) and Any WMH Total (Fazekas score 1–6)

Severe DWMH (Score≥2), Severe PWMH (Score≥2), and Severe WMH (Score≥4)

MEG data were recorded using a MEG scanner with 151 axial gradiometers (Omega-151; CTF, Coquitlam, BC, Canada) in a magnetically shielded room at the Hospital for Sick Children (sampling rate: 600 Hz, filters: 0–150 Hz, third-order spatial gradient noise cancellation). Head position was continuously recorded by coils placed on three fiducial points on the subject’s head (nasion, left and right pre-auricular points). After the MEG session, T₁-weighted MRI scans were acquired in all participants on a Siemens 3T system; fiducial points from the MEG session were recorded on MRI images to allow precise MEG/MRI co-registration.