Age-related changes in the pediatric brain: quantitative MR evidence of maturational changes during adolescence.

PURPOSE: To determine whether a quantitative MR imaging method to map spin-lattice relaxation time (T1) can be used to characterize maturational changes in the normal human brain.
METHODS: An inversion-recovery technique was used to map T1 transversely at the level of the basal ganglia in a study population of 19 healthy children (4 to 10 years old) and 31 healthy adolescents (10 to 20 years old), and in a normative population of 20 healthy adults (20 to 30 years old).
RESULTS: Nonparametric analysis of variance showed that T1 decreases with age in the genu, frontal white matter, caudate, putamen, anterior thalamus, pulvinar nucleus, optic radiation, cortical gray matter (all P < .0001), and occipital white matter. There was a significant reduction in T1 between childhood (mean age, 7.1 +/- 1.4) and adolescence (mean age, 13.5 +/- 2.6) in all brain structures, but there was also a significant reduction in T1 between adolescence (mean age, 13.5 +/- 2.6) and adulthood (mean age, 26.5 +/- 3.4) in all brain structures except occipital white matter. Regression shows that T1 declines to within the range (mean +/- 2 SD) of young adult T1 values by about 2 years in the occipital white matter, by about 4 years in the genu, by 11 years in the cortical gray matter, by 11 years in the frontal white matter, and by 13 years in the thalamus.
CONCLUSION: Brain structures mature at strikingly different rates, yet the ratio of gray matter T1 to white matter T1 does not change significantly with age. Thus, conventional MR imaging methods based on inherent contrast are insensitive to these changes. Age-related changes tend to reach completion sooner in white matter than in gray matter tracts. Such normative data are essential for studies of specific pediatric disorders and may be useful for assessing brain maturation in cases of developmental delay.