Abstract
BackgroundAxonal myelination is an important maturation process in the developing brain. Increasing myelin content correlates with the longitudinal relaxation rate (R1=1/T1) in magnetic resonance imaging (MRI).ObjectiveBy using magnetization-prepared 2 rapid acquisition gradient echoes (MP2RAGE) on a 3-T MRI system, we provide R1 values and myelination rates for infants and young children.Materials and methodsAverage R1 values in white and grey matter regions in 94 children without pathological MRI findings (age range: 3 months to 6 years) were measured and fitted by a saturating-exponential growth model. For comparison, R1 values of 36 children with different brain pathologies are presented. The findings were related to a qualitative evaluation using T2, magnetization-prepared rapid acquisition gradient echo (MP-RAGE) and MP2RAGE.ResultsR1 changes rapidly in the first 16 months of life, then much slower thereafter. R1 is highest in pre-myelinated structures in the youngest subjects, such as the posterior limb of the internal capsule (0.74–0.76±0.04 s−1) and lowest for the corpus callosum (0.37–0.44±0.03 s−1). The myelination rate is fastest in the corpus callosum and slowest in the deep grey matter. R1 is decreased in hypo- and dysmyelination disorders. Myelin maturation is clearly visible on MP2RAGE, especially in the first year of life.ConclusionMP2RAGE permits a quantitative R1 mapping method with an examination time of approximately 6 min. The age-dependent R1 values for children without MRI-identified brain pathologies are well described by a saturating-exponential function with time constants depending on the investigated brain region. This model can serve as a reference for this age group and to search for indications of subtle pathologies. Moreover, the MP2RAGE sequence can also be used for the qualitative assessment of myelinated structures.
Highlights
Myelination is a highly regulated process, primarily taking place in early childhood but continuing at a slower pace in older children and adolescents [1, 2]
We measured R1 values in the white and deep grey matter of magnetic resonance imaging (MRI)-negative children using a high-resolution magnetization-prepared 2 rapid acquisition gradient echoes (MP2RAGE) sequence with the aim of describing the change in R1 in young children as a result of increasing myelination, and evaluating a quantitative R1 mapping method that is applicable in the clinical practice
We found that the myelination rate in the corpus callosum is faster than that in the centrum semiovale
Summary
Myelination is a highly regulated process, primarily taking place in early childhood but continuing at a slower pace in older children and adolescents [1, 2]. The assessment of myelination is an integral part of any magnetic resonance imaging (MRI) examination in young children in order to detect myelination disorders and to evaluate potential secondary injuries in the brain. This is performed by qualitatively comparing predefined white matter. The agedependent R1 values for children without MRI-identified brain pathologies are well described by a saturating-exponential function with time constants depending on the investigated brain region. This model can serve as a reference for this age group and to search for indications of subtle pathologies. The MP2RAGE sequence can be used for the qualitative assessment of myelinated structures
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