Fractional anisotropy values of brain matter among healthy children: cohort study

Abstract

INTRODUCTION: Diffusion-tensor magnetic resonance imaging (DT-MRI) is currently a well studied and applied in clinical practice technique. An important advantage of this technique is the measurement of fractional anisotropy (FA) values, which make it possible to quantify changes in brain matter. The authors are aware of publications on the study of FА values among children in small groups including only a part of ages. This work presents study of FA among large amount of examined children and notes values of FA for most of the significant structures of the brain in subjects from 4 months to 18 years of age.OBJECTIVE: Analysis of the FА values of the anatomical structures of the brain in children of different age groups who did not reveal changes in the brain matter during multiparametric MRI, in order to further study the processes of development and myelination of brain structures, as well as the use of these values in clinical practice as reference values in the analysis of pathology.MATERIALS AND METHODS: 153 patients aged from 4 months to 18 years were examined. MRI of brain was performed on the recommendation of the attending physician in accordance with clinical indications in case of suspected infection in the paranasal sinuses and neurological complaints, without focal symptoms. Distribution of examined children by age groups was: up to 1 year (infant age) — 6 children (3.9%); from 1 year to 3 years (early childhood) — 14 children (9.15%); from 3 to 7 years old (preschool age) — 39 children (25.5%); older than 7 years (school age and older) — 94 children (61.45%). Distribution of the examined by gender: male children — 82 (53.6%); female — 71 (46.4%). DT-MRI was applied to all patients with measurement of diffusion in 15 directions, and then FА values were measured in 21 areas of the white and gray matter of the brain. The regions of interest (ROI) were arranged in accordance with the zones of the ASPECTS and PC-ASPECTS scales adapted for the purposes of this study. Statistics: processing of the received data was carried out using application programs: Microsoft Excel, Statistica 10 with an assessment of the normality of the distribution of values and the use of parametric and nonparametric criteria.RESULTS: The highest mean numerical values of FA for all groups of children were found in the white matter along neural pathways: 0.66±0.04 for the internal capsule; 0.68±0.05 — in the white matter of the midbrain; 0.64±0.08 — at the level of the pons; 0.69±0.04 — in the cerebellar peduncles. The FA indices in the white matter of other anatomical regions are slightly lower: 0.50±0.08 — for white matter at the M4 level according to ASPECTS; 0.52±0.08 — in the occipital lobe at the level of the basal ganglia; 0.54±0.05 — in the temporal lobe. The lowest FA values appeared in the gray matter: 0.16±0.04 — in the caudate nucleus; 0.12±0.04 — in the gray matter at the M4 level according to ASPECTS. The most pronounced differences in FA in children of early childhood and school age appeared in the ROI located in the white matter of the cerebral cortex: in the area of M5 0.46±0.05 versus 0.54±0.05, respectively; in the area of M1 0.43±0.06 versus 0.51±0.06, respectively. At the same time, differences in FA in children of early childhood and school age in ROI located in the white matter at the level of stem structures are less pronounced: at the level of the pons 0.6±0.07 versus 0.64±0.07, respectively; at the level of the cerebellar peduncles 0.68±0.04 versus 0.69±0.04, respectively. These numerical indicators illustrate and additionally confirm the known ideas about the development and formation of neural pathways and about the processes of their myelination. They also reflect the known data on the structural and functional differences between the gray and white matter of the brain. A significant increase of the FА values in children older than 7 years was determined in comparison with groups of younger children in the white matter of the cortical structures of the brain. At the same time, there are no significant age-related differences of FА in the region of brainstem. It was also found that in preschoolers, compared with children from 1 to 3 years old, white matter FА increases in the region of the caudate nucleus and midbrain.CONCLUSION: The obtained normative values of FА can later be widely used in clinical practice as reference ones when performing DT-MRI and assessing neuroinfectious and other pathological changes in the brain matter in children. The revealed differences in age groups indicate an earlier development of brainstem structures, while the subcortical-cortical areas of the cerebral hemispheres develop and myelinate over a longer time.