Structural, Functional, and Diffusion MRI Analysis in ELBW Infants

Structural, diffusion, and resting-state functional MRIs were acquired on a Siemens 3T Trio Tim scanner using a 24-channel phased-array head coil. Diffusion tensor imaging and resting-state functional MRI scans were obtained with the same scanner using an identical protocol for all participants during a single visit. The Tracts Constrained by Underlying Anatomy (TRACULA) tool within FreeSurfer 7.1²⁴ was used for diffusion tensor imaging data processing and tractography to estimate the posterior probability of the 18 major white matter tracts. Among the 18 tracts, there were 5 tracts with segments that showed significant differences in both fractional anisotropy (FA) and mean diffusivity (MD) among the ELBW group (with or without PGF): the forceps major of the corpus callosum (Fmajor), right anterior thalamic radiation (RATR), left inferior longitudinal fasciculus, left superior longitudinal fasciculus–parietal bundle (LSLFP), and left superior longitudinal fasciculus–temporal bundle (Figure 1). The CONN toolbox²⁵ was used for the seed-based functional connectivity analysis.^{26 (link)} To select the region of interest as a seed, the multivoxel–multivariate pattern analysis method was used, which showed group differences in 4 regions: the precuneus, the left and right superior lateral occipital cortex (sLOC), and the posterior cingulate cortex (PCC) (eFigure 2 in Supplement 1). A seed-based functional connectivity analysis was performed for whole-brain regions with the selected 4 regions of interest in the multivoxel–multivariate pattern analysis. Functional connectivity strength values were extracted from the brain regions of the preterm infants (uncorrected height threshold of P < .001 and cluster-level false discovery rate–corrected P < .05). The diffusion metrics of the selected tracts and the FCS values were used in the correlational analysis with clinical and neuropsychological measures. Details are provided in the eMethods in Supplement 1.