Mr750 scanner

Lumbar scans were performed on a 3T GE MR750 scanner and sequences included standard clinical T1- and T2-weighted MRI sequences and advanced sequences used for cartilage endplate detection (high-resolution 3D ultrashort echo time, UTE^{25 (link)} and fat fraction measurement (Iterative Decomposition of water and fat with Echo Asymmetry and Least-Squares Estimation, IDEAL^{26 (link)} (Figure 1). Specifications for the UTE sequence included TE=0.075 ms, TR=10 ms, voxel size of 0.22×0.22×0.80 mm³, and fat suppression. Specifications for the IDEAL sequence included TR=7ms, TE=2.1ms, flip angle=3°, rBW=±83.3kHz, FoV=22cm, in-plane resolution=1.3mm, and slice thickness=4mm).

[¹⁸F]-FEPPA was synthesized as previously described.^{15 (link)} All subjects underwent one [¹⁸F]-FEPPA PET scan and one MRI scan. The MRI scans of 14 healthy control subjects were acquired with a General Electric (Milwaukee, WI, USA) Signa 1.5 Tesla MRI scanner. The other 7 control subjects and all participants with AD had the T₁ weighted images acquired on a 3-Tesla General Electric MR750 scanner. MRI acquisition parameters for both scanners have been described in detail elsewhere.^{45 (link)} The PD-weighted and T₂ FLAIR scans were visually inspected for evidence of focal and vascular lesions including the presence of white matter hyperintensities, which was determined by following established criteria.^{46 (link)}The PET images were obtained for 125 min following the injection of [¹⁸F]-FEPPA using a 3D high-resolution research tomograph brain tomograph (CS/Siemens, Knoxville, TN, USA) as previously described.^{16 (link)} A dose of 181±15 mBq of intravenous [¹⁸F]-FEPPA was administered as a bolus for the PET scan. Blood samples were collected for genotyping of TSPO rs6971 polymorphism and for obtaining the arterial input function used for the kinetic analysis of [¹⁸F]FEPPA, as previously described.^{16 (link)}

MRI scans were acquired on a 3T GE MR750 scanner with an 8-channel head-coil at the Duke-UNC Brain Imaging and Analysis Center. High-resolution T1-weighted images were collected using a 3D fast spoiled-gradient-recalled sequence (TR/TE=8.2/3.22ms; FA=12°; FOV=240×240×166mm²; matrix size=256×256×166; slice thickness=1mm). Functional images during the MIST were acquired using a spiral-in sensitivity encoding interleaved sequence (TR/TE=2000/30ms, FA=60°, FOV=24cm, acquisition matrix=64×64, slice thickness=4mm, 34 slices) (31 (link)).

Imaging was conducted on a 3.0 Tesla General Electric MR750 scanner (gehealthcare.com) using an 8-channel head coil. fMRI scans used a spiral in/out pulse sequence [46 (link)] with the following parameters: 30 axial slices (3mm thick, 1mm skip) parallel to the AC-PC line and covering the whole brain. TR=2000 msec, TE=30msec, flip angle=90°, FOV=22cm², 64×64 matrix, in-plane spatial resolution of 3.125mm. Shimming reduced blurring and signal loss from field inhomogeneities.
We conducted image pre-processing using FMRIB Software Library (FSL), www.fmrib.ox.ac.uk/fsl. This included motion correction, skull stripping, spatial smoothing of 5mm full-width/half-maximum Gaussian kernel, mean-based intensity normalization of all volumes by the same factor, and high-pass temporal filtering with 60s cutoff. We did not utilize slice-timing correction in order to avoid interpolation of data. We coregistered functional images of each participant to corresponding structural images in native space (2-step registration, which included a high-resolution T1-weighted 3D inversion recovery spoiled gradient-recalled acquisition scan, as well as a matched-bandwidth Tl-weighted image collected in the same plane as the functional scans), and registered structural images to structural standard images, defined by the Montreal Neurological Institute averaged 152 standard brain.

MRI data were acquired on a 3-Tesla General Electric MR750 scanner with a 32-channel head coil. A high-resolution, T1-weighted fast spoiled gradient echo sequence was acquired in the sagittal plane (TR = 7.1 ms; TE = min full; inversion time [TI] = 500 ms; flip angle = 11°; 176 slices; 1.0 mm slice thickness; field of view [FOV] = 25 cm; inplane resolution = 1.0 by 1.0 mm). All images were visually inspected for motion artifacts and ghosting, resulting in the exclusion of 15 participants’ MRI data from analyses. There was no manual editing of imaging data that passed quality control procedures.