Individual fibre inclination segmentation from X-ray computed tomography using principal component analysis

This study presents a holistic segmentation procedure, which can be used to obtain individual fibre inclination angles from X-ray computed tomography. The segmentation approach is based on principal component analysis and was successfully applied for a unidirectional and an air-textured glass fibre–reinforced composite profile. The inclination results show a weighted mean fibre inclination of 2.1° and 8.0° for the unidirectional and air-textured profile, respectively. For the air-textured composite, fibre inclinations of up to 55° were successfully segmented. The results were verified by comparative analysis with equivalent results obtained from structure tensor analysis – showing no notable deviation. The comparable characteristics in combination with the distinct differences of the two material systems make this case study ideal for verification and validation of idealized models. It is shown how this approach can provide fast, accurate and repeatable inclination estimates with a high degree of automation.

Long-term development of white matter fibre density and morphology up to 13 years after preterm birth

BackgroundIt is well documented that infants born very preterm (VP) are at risk of brain injury and altered brain development in the neonatal period, however there is a lack of long-term, longitudinal studies on the effects of VP birth on white matter development over childhood. Most previous studies were based on voxel-averaged, non-fibre-specific diffusion magnetic resonance imaging (MRI) measures, such as fractional anisotropy. In contrast, the novel diffusion MRI analysis framework, fixel-based analysis (FBA), enables whole-brain analysis of microstructural and macrostructural properties of individual fibre populations at a sub-voxel level. We applied FBA to investigate the long-term implications of VP birth and associated perinatal risk factors on fibre development in childhood and adolescence.MethodsDiffusion images were acquired for a cohort of VP (born <30 weeks’ gestation) and full-term (FT, ≥37 weeks’ gestation) children at two ages: mean (SD) 7.6 (0.2) years (n=138 VP and 32 FT children) and 13.3 (0.4) years (n=130 VP and 45 FT children). 103 VP and 21 FT children had images at both ages for longitudinal analysis. At every fixel (individual fibre population within an image voxel) across the white matter, we compared FBA metrics (fibre density (FD), cross-section (FC) and a combination of these properties (FDC)) between VP and FT groups cross-sectionally at each age, and longitudinally between ages. We also examined associations between perinatal risk factors and FBA metrics in the VP group.ResultsCompared with FT children, VP children had lower FD, FC and FDC throughout the white matter, particularly in the corpus callosum, tapetum, inferior fronto-occipital fasciculus, fornix and cingulum at ages 7 and 13 years, as well as the motor pathways at age 13 years. VP children also had slower FDC development in the corpus callosum and corticospinal tract between ages 7 and 13 years compared with FT children. Within VP children, earlier gestational age at birth, lower birth weight z-score, and neonatal brain abnormalities were associated with lower FD, FC and FDC throughout the white matter at both ages.ConclusionsVP birth and concomitant perinatal risk factors are associated with fibre tract-specific alterations to axonal development in childhood and adolescence.