Longitudinal Structural Brain Imaging

MR images were obtained on a 1.5-T GE Signa MRI scanner (GE Healthcare, Waukesha, WI, USA). T1-weighted images were acquired using a three-dimensional (3D) spoiled gradient recall (SPGR) with imaging parameters: repetition time (TR)=24ms, echo time (TE)=5ms, flip angle=40°, thickness=1.5mm, slices=124, plane=coronal, field-of-view (FOV)=20cm, matrix=256×256. Processing of T1-weighted images was performed with the software Freesurfer (http://freesurfer.net) (version 5.3) using the recon-all pipeline^{38 –39 (link)}. Details regarding image processing can be found in a previous publication^{24 (link)}. In short, we performed automatic cortical surface parcellation and subcortical structures segmentation, with cortical volume changes calculated using Freesurfer’s processing stream for longitudinal images^{40 (link)}. Once both baseline and follow-up scans were longitudinally processed, the change in volume between time points normalized to the baseline evaluation ((TP₂-TP₁)/TP₁) was calculated. Aside from calculations of prospective development, baseline volumes also underwent GT investigations in order to study possible associations to neurocognitive measures. Baseline volumes were obtained from the longitudinally processed data.