MR assessment of the brain maturation during the perinatal period: quantitative T 2 MR study in premature newborns

Abstract

The purpose of our study is to trace in vivo and during the perinatal period, the brain maturation process with exhaustive measures of the T 2 relaxation time values. We also compared regional myelination progress with variations of the relaxation time values and of brain signal. T 2 relaxation times were measured in 7 healthy premature newborns at the post-conceptional age of 37 weeks, using a Carr-Purcell-Meiboom-Gill sequence (echo time 60 to 150 ms), on a 2.35 Tesla Spectro-Imaging MR system. A total of 62 measures were defined for each subject within the brain stem, the basal ganglia and the hemispheric gray and white matter. The mean and standard deviation of the T 2 values were calculated for each location. Regional T 2 values changes and brain signal variations were studied. In comparison to the adult ones, the T 2 relaxation time values of both gray and white matter were highly prolonged and a reversed ratio between gray and white matter was found. The maturational phenomena might be regionally correlated with a T 2 value shortening. Significant T 2 variations in the brainstem ( p < 0.02), the mesencephalon ( p < 0.05), the thalami ( p < 0.01), the lentiform nuclei ( p < 0.01) and the caudate nuclei ( p < 0.02) were observed at an earlier time than they were visible on T 2-weighted images. In the cerebral hemispheres, T 2 values increased from the occipital white matter to parietal, temporal and frontal white matter ( p < 0.05) and in the frontal and occipital areas from periventricular to subcortical white matter ( p < 0.01). Maturational progress was earlier and better displayed with T 2 measurements and T 2 mapping. During the perinatal period, the measurements and analysis of T 2 values revealed brain regional differences not discernible with T 2-weighted images. It might be a more sensitive indicator for assessment of brain maturation.