Brain MRI Volumetric Analysis Protocol

Magnetic resonance imaging (MRI) of the brain was also completed at Emory University (3.0-T Trio MRI scanner; Siemens Medical Solutions). High-resolution T1-weighted images were acquired using a magnetization-prepared rapid gradient-echo imaging sequence with field of view of 256 × 256 mm²; 176 sagittal slices; isotropic voxel resolution, 1.0 mm³; repetition time, 2300 milliseconds; echo time, 2.89 milliseconds; inversion time, 800 milliseconds; flip angle, 8°; and scan duration, 8 minutes 37 seconds. Quality checks included head motion detection and/or correction, atlas registration confirmation, and visual inspection of images.
Hippocampal volume and other volumetric measurements were calculated using the FreeSurfer package, version 6.0.0, with manual supervision. Quality checks were performed for each scan. Left and right hippocampal volumes were obtained and combined to derive the total hippocampal volume. Intracranial volume was also derived from this analysis. Volumetric measurements using FreeSurfer have been shown to provide similar estimates to a fully manual procedure.^{16 (link)} We used intracranial volume–adjusted hippocampal volume to reflect the degree of neurodegeneration for each participant.^{4 (link)}