The normal neonatal brain: MR imaging, diffusion tensor imaging, and 3D MR spectroscopy in healthy term neonates

Abstract

Background and purpose: There is a lack of normative diffusion tensor imaging (DTI) and 3D MR spectroscopy (MRS) data in the early neonatal period. We report quantitative values from a cohort of healthy term neonates to serve as baseline data for studies assessing brain development and injury.

Materials and methods: Sixteen healthy term neonates (median age, 7 days) were studied with spin-echo T1- and T2-weighted MR imaging, DTI, and 3D point-resolved spectroscopy sequence (PRESS) MRS without sedation on a 1.5 T scanner. Average diffusivity (D(av)), fractional anisotropy (FA), eigenvalues (EV), and metabolite ratios (N-acetylaspartate [NAA]/choline, lactate/choline) were calculated by automated processing in 7 brain regions. Neurodevelopment was assessed by blinded and validated neuromotor examinations and the Bayley II test at 3 and 14 months.

Results: Two neonates were excluded from the cohort: one had brain injury on T2-weighted imaging, and the other, who had normal MR imaging, showed mildly delayed cognition at 14 months. The mean DTI values of the remaining 14 neonates were between these ranges: D(av)=0.98-1.48 10(-3) mm(2)/s, FA=0.14-0.30, EV1=1.21-1.88, EV2=0.95-1.46, and EV3=0.77-1.24 (all x 10(-3) mm(2)/s). The NAA/choline ratio ranged between 0.58 and 0.73, and minimal lactate/choline (<0.15) could be detected in each neonate. All neonates exhibited clinically normal neuromotor status.

Conclusions: Our study demonstrates the feasibility of obtaining high-quality quantifiable MR data in nonsedated healthy term neonates that can be used to study normal early brain development and as control data in studies of perinatal brain injury.

Figures

Fig 1.

Locations of regions of interest for MRS and DTI measurements are marked by rectangles as follows:) basal ganglia (1), thalami (2), calcarine cortex (3), optic radiations (4), corticospinal tracts (5), posterior white matter (6), frontal white matter (7). A, Squares showing region of interest locations from which proton spectra ratios were acquired and calculated by automated processing after the MR study of every neonate. B, Squares showing the regions of interest from which Dav, FA, and eigenvalues were calculated by automated processing.

Fig 2.

3D MR spectroscopy imaging on a single plane at the level of the basal ganglia illustrates the variation in maturity of metabolites in different regions of a healthy term neonate. Note that the thalami have the most mature spectra, with lowest choline and highest NAA peaks, and the frontal white matter has the least mature spectra.