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Preterm birth has been associated with altered microstructural properties of the white matter and lower cognitive ability in childhood and adulthood. Due to methodological limitations of the diffusion tensor model, it is not clear whether alterations in myelination or variation in fibre orientation are driving these differences. Novel models applied to multi‐shell diffusion imaging have been used to disentangle these effects, but to date this has not been used to study the preterm brain in adulthood. This study investigated whether novel advanced diffusion MRI metrics such as microscopic anisotropy and orientation dispersion are altered in adults born preterm, and whether this was associated with cognitive performance. Seventy‐two preterm born participants (<37 weeks gestational age) were recruited from a 1982–1984 cohort (33 males, mean age 33.5 ± 1.0 years). Seventy‐two term born (>37 weeks gestational age) controls (34 males, mean age 30.9 ± 4.0 years) were recruited from the general population. Tensor FA was calculated with FSL, while microscopic FA and orientation dispersion entropy (ODE) were estimated using the Spherical Mean Technique (SMT). Estimated Full Scale IQ (FSIQ), Verbal Comprehension Index (VCI) and Perceptual Reasoning Index (PRI) were obtained from the WASI‐II (abbreviated) IQ test. Voxel‐wise comparisons using FSL's tract‐based spatial statistics were performed to test between‐group differences in diffusion MRI metrics as well as within‐group associations of diffusion MRI metrics and IQ outcomes. The preterm group had significantly lower FSIQ, VCI and PRI scores. Preterm subjects demonstrated widespread decreases in ODE reflecting increased fibre dispersion, but no differences in microscopic FA. Tensor FA was increased in a small area in the anterior corona radiata. Lower FA values in the preterm population were associated with lower FSIQ and PRI scores. An increase in fibre dispersion in white matter and lower IQ scores after preterm birth exist in adulthood. Advanced diffusion MRI metrics such as the orientation dispersion entropy can be used to monitor white matter alterations across the lifespan in preterm born individuals. Although not significantly different between preterm and term groups, tensor FA values in the preterm group were associated with cognitive outcome. [ABSTRACT FROM AUTHOR]

The growth hormone-insulin-like growth factor-1 axis plays a role in normal brain growth but little is known of the effect of growth hormone deficiency on brain structure. Children with isolated growth hormone deficiency (peak growth hormone less than 6.7 [micro]g/l) and idiopathic short stature (peak growth hormone greater than 10 [micro]g/l) underwent cognitive assessment, diffusion tensor imaging and volumetric magnetic resonance imaging prior to commencing growth hormone treatment. Total brain, corpus callosal, hippocampal, thalamic and basal ganglia volumes were determined using Freesurfer. Fractional anisotropy (a marker of white matter structural integrity) images were aligned and tract-based spatial statistics performed. Fifteen children (mean 8.8 years of age) with isolated growth hormone deficiency [peak growth hormone less than 6.7 [micro]g/l (mean 3.5 [micro]g/l)] and 14 controls (mean 8.4 years of age) with idiopathic short stature [peak growth hormone greater than 10 [micro]g/l (mean 15 [micro]g/l) and normal growth rate] were recruited. Compared with controls, children with isolated growth hormone deficiency had lower Full-Scale IQ (P less than 0.01), Verbal Comprehension Index (P less than 0.01), Processing Speed Index (P less than 0.05) and Movement-Assessment Battery for Children (P less than 0.008) scores. Verbal Comprehension Index scores correlated significantly with insulin-like growth factor-1 (P less than 0.03) and insulin-like growth factor binding protein-3 (P less than 0.02) standard deviation scores in isolated growth hormone deficiency. The splenium of the corpus callosum, left globus pallidum, thalamus and hippocampus (P less than 0.01) were significantly smaller; and corticospinal tract (bilaterally; P less than 0.045, P less than 0.05) and corpus callosum (P less than 0.05) fractional anisotropy were significantly lower in the isolated growth hormone deficiency group. Basal ganglia volumes and bilateral corticospinal tract fractional anisotropy correlated significantly with Movement-Assessment Battery for Children scores, and corpus callosum fractional anisotropy with Full-Scale IQ and Processing Speed Index. In patients with isolated growth hormone deficiency, white matter abnormalities in the corpus callosum and corticospinal tract, and reduced thalamic and globus pallidum volumes relate to deficits in cognitive function and motor performance. Follow-up studies that investigate the course of the structural and cognitive deficits on growth hormone treatment are now required to confirm that growth hormone deficiency impacts significantly on brain structure, cognitive function and motor performance.

Since the invention of diffusion magnetic resonance imaging (dMRI), currently the only established method for studying white matter connectivity in a clinical environment, there has been a great deal of interest in the effects of various pathologies on the connectivity of the brain. As methods for in vivo tractography have been developed, it has become possible to track and segment specific white matter structures of interest for particular study. However, the consistency and reproducibility of tractography-based segmentation remain limited, and attempts to improve them have thus far typically involved the imposition of strong constraints on the tract reconstruction process itself. In this work we take a different approach, developing a formal probabilistic model for the relationships between comparable tracts in different scans, and then using it to choose a tract, a posteriori, which best matches a predefined reference tract for the structure of interest. We demonstrate that this method is able to significantly improve segmentation consistency without directly constraining the tractography algorithm. Index Terms--Brain, diffusion, magnetic resonance imaging, model, probabilistic, tractography, segmentation, white matter.