Structures Showing Negative Correlations of Signal Intensity with Postnatal Age on T 1 -weighted Imaging of the Brain of Newborns and Infants.

Purpose: Although the neonatal and infantile brain typically shows sequential T-1 shortening according to gestational age as a result of myelination, several structures do not follow this rule. We evaluated the relationship between the signal intensity of various structures in the neonatal and infantile brain on T-1-weighted imaging (T1WI) and either postnatal or gestational age. Materials and Methods: We examined magnetic resonance images from 120 newborns and infants without any abnormalities in the central nervous system. Written informed consent was obtained from all parents and the institutional review board approved the study. Gestational age at examination ranged from 35 weeks, 3 days to 46 weeks, 6 days, and postnatal age ranged from 7 days to 127 days. Signal intensity on T1WI was evaluated on a scale from Grade 1 (indistinguishable from surrounding structures) to Grade 4 (higher than cortex and close to fat). We evaluated relationships between the T-1 signal grades of various structures in the neonatal brain and postnatal or gestational age using Spearman's correlation analysis. Results: Significant positive correlations were identified between T-1 signal grade and gestational age in the pyramidal tract (P < 0.001). Conversely, significant negative correlations were evident between T-1 signal grade and postnatal age (P < 0.001), in structures including the stria medullaris thalami, fornix cerebellar vermis, dentate nucleus and anterior pituitary gland. Conclusion: Significant negative correlations exist between signal intensity on T1WI and postnatal age in some structures of the neonatal and infantile brain. Some mechanisms other than myelination might play roles in the course of signal appearance.