Abstract
PurposeDiffusion magnetic resonance imaging (dMRI) studies report altered white matter (WM) development in preterm infants. Neurite orientation dispersion and density imaging (NODDI) metrics provide more realistic estimations of neurite architecture in vivo compared with standard diffusion tensor imaging (DTI) metrics. This study investigated microstructural maturation of WM in preterm neonates scanned between 25 and 45 weeks postmenstrual age (PMA) with normal neurodevelopmental outcomes at 2 years using DTI and NODDI metrics.MethodsThirty-one neonates (n = 17 male) with median (range) gestational age (GA) 32+1 weeks (24+2–36+4) underwent 3 T brain MRI at median (range) post menstrual age (PMA) 35+2 weeks (25+3–43+1). WM tracts (cingulum, fornix, corticospinal tract (CST), inferior longitudinal fasciculus (ILF), optic radiations) were delineated using constrained spherical deconvolution and probabilistic tractography in MRtrix3. DTI and NODDI metrics were extracted for the whole tract and cross-sections along each tract to assess regional development.ResultsPMA at scan positively correlated with fractional anisotropy (FA) in the CST, fornix and optic radiations and neurite density index (NDI) in the cingulum, CST and fornix and negatively correlated with mean diffusivity (MD) in all tracts. A multilinear regression model demonstrated PMA at scan influenced all diffusion measures, GA and GAxPMA at scan influenced FA, MD and NDI and gender affected NDI. Cross-sectional analyses revealed asynchronous WM maturation within and between WM tracts.).ConclusionWe describe normal WM maturation in preterm neonates with normal neurodevelopmental outcomes. NODDI can enhance our understanding of WM maturation compared with standard DTI metrics alone.
Highlights
The incidence of preterm birth is increasing, impacting around 12–13% of all live births in the United States of America (USA) and 5–9% in other developed countries [1]
We investigated how diffusion tensor imaging (DTI) and Neurite orientation dispersion and density imaging (NODDI) metrics changed with postmenstrual age (PMA) at scan, the relationship between DTI and NODDI metrics, factors that influenced diffusion measures within the tract and regional differences in white matter (WM) maturation
Increasing PMA at scan was associated with decreasing mean diffusivity (MD) and increasing fractional anisotropy (FA) and neurite density index (NDI)
Summary
The incidence of preterm birth is increasing, impacting around 12–13% of all live births in the United States of America (USA) and 5–9% in other developed countries [1]. Survivors of preterm birth have a high prevalence of neurodevelopmental impairments, including cognitive deficits, developmental coordination disorder and behavioural problems [2, 3]. Diffusion magnetic resonance imaging (dMRI) studies have identified altered white matter (WM) development in preterm infants [4, 5], which is associated with neurodevelopmental impairments [6, 7]. Increasing our understanding of WM microstructural development between birth and term equivalent age in preterm infants with normal neurodevelopment in early childhood may be Neuroradiology (2021) 63:573–583 informative to identify early markers of abnormal WM development and those at risk of adverse neurodevelopmental outcomes. WM development begins in the foetal brain around 13– 18 weeks post-conception with limbic, projection and commissural pathways, followed by thalamocortical and association pathways around 24–32 weeks and continues to rapidly develop during the first 2 years of life [8]. Histological studies have identified several distinct stages of WM development: axonal formation, neuronal and synaptic overproduction (preserving neuronal plasticity), elimination and pruning (creating more organised and streamlined networks), pre-myelination (the maturation of oligodendrocytes forming the myelin sheath) and myelination (the ensheathment of oligodendroglial processes around the axons to provide rapid and efficient conduction of nervous impulses improving brain connectivity) [9,10,11]
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