195 research outputs found

    A tract-specific approach to assessing white matter in preterm infants.

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    Diffusion-weighted imaging (DWI) is becoming an increasingly important tool for studying brain development. DWI analyses relying on manually-drawn regions of interest and tractography using manually-placed waypoints are considered to provide the most accurate characterisation of the underlying brain structure. However, these methods are labour-intensive and become impractical for studies with large cohorts and numerous white matter (WM) tracts. Tract-specific analysis (TSA) is an alternative WM analysis method applicable to large-scale studies that offers potential benefits. TSA produces a skeleton representation of WM tracts and projects the group's diffusion data onto the skeleton for statistical analysis. In this work we evaluate the performance of TSA in analysing preterm infant data against results obtained from native space tractography and tract-based spatial statistics. We evaluate TSA's registration accuracy of WM tracts and assess the agreement between native space data and template space data projected onto WM skeletons, in 12 tracts across 48 preterm neonates. We show that TSA registration provides better WM tract alignment than a previous protocol optimised for neonatal spatial normalisation, and that TSA projects FA values that match well with values derived from native space tractography. We apply TSA for the first time to a preterm neonatal population to study the effects of age at scan on WM tracts around term equivalent age. We demonstrate the effects of age at scan on DTI metrics in commissural, projection and association fibres. We demonstrate the potential of TSA for WM analysis and its suitability for infant studies involving multiple tracts

    Diffusion tensor imaging: application to the study of the developing brain

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    pre-printObjective: To provide an overview of diffusion tensor imaging (DTI) and its application to the study of white matter in the developing brain, in both healthy and clinical samples. Method: The development of DTI and its application to brain imaging of white matter tracts is discussed. 48 studies using DTI to examine diffusion properties of the developing brain are reviewed in the context of the structural magnetic resonance imaging (MRI) literature. Reports of how brain diffusion properties are affected in pediatric clinical samples and how they relate to cognitive and behavioral phenotypes are reviewed. Results: DTI has been successfully used to describe white matter development in pediatric samples. Changes in white matter diffusion properties are consistent across studies, with anisotropy increasing and overall diffusion decreasing with age. Diffusion measures in relevant white matter regions correlate with behavioral measures in healthy children and in clinical pediatric samples. Conclusions: DTI is an important tool for providing a more detailed picture of developing white matter than can be obtained with conventional MRI alone. Keywords: brain, development, white matter, diffusion tensor imaging, magnetic resonance imaging

    Diffusion Tensor Imaging as a Diagnostic and Research Tool: A Study on Preterm Infants

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    Diffusion tensor imaging (DTI) is an advanced magnetic resonance imaging (MRI) technique. DTI is based on free thermal motion (diffusion) of water molecules. The properties of diffusion can be represented using parameters such as fractional anisotropy, mean diffusivity, axial diffusivity, and radial diffusivity, which are calculated from DTI data. These parameters can be used to study the microstructure in fibrous structure such as brain white matter. The aim of this study was to investigate the reproducibility of region-of-interest (ROI) analysis and determine associations between white matter integrity and antenatal and early postnatal growth at term age using DTI. Antenatal growth was studied using both the ROI and tract-based spatial statistics (TBSS) method and postnatal growth using only the TBSS method. The infants included to this study were born below 32 gestational weeks or birth weight less than 1,501 g and imaged with a 1.5 T MRI system at term age. Total number of 132 infants met the inclusion criteria between June 2004 and December 2006. Due to exclusion criteria, a total of 76 preterm infants (ROI) and 36 preterm infants (TBSS) were accepted to this study. The ROI analysis was quite reproducible at term age. Reproducibility varied between white matter structures and diffusion parameters. Normal antenatal growth was positively associated with white matter maturation at term age. The ROI analysis showed associations only in the corpus callosum. Whereas, TBSS revealed associations in several brain white matter areas. Infants with normal antenatal growth showed more mature white matter compared to small for gestational age infants. The gestational age at birth had no significant association with white matter maturation at term age. It was observed that good early postnatal growth associated negatively with white matter maturation at term age. Growth-restricted infants seemed to have delayed brain maturation that was not fully compensated at term, despite catchup growth.Diffuusiotensorikuvaus diagnostisena ja tutkimustyökaluna keskostutkimuksessa Diffuusiotensorikuvaus (DTI) on magneettikuvauksen erikoistekniikka. DTI perustuu veden vapaaseen lämpöliikkeeseen (diffuusioon). Diffuusion ominaisuuksia voidaan esittää DTI-datasta laskettavien parametrien avulla. Tällaisia parametreja ovat esimerkiksi fraktionaalinen anisotropia, keskimääräinen diffusiviteetti, aksiaalinen ja radiaalinen diffusiviteetti. Näitä parametrejä voidaan käyttää säikeisten rakenteiden esimerkiksi aivojen valkoisen aineen tutkimiseen. Tässä tutkimuksessa selvitettiin keskosten aivojen diffuusiotensorikuvista tehtyjen mielenkiintoalueisiin (ROI) perustuvien mittausten toistettavuutta sekä tutkittiin valkoisen aineen kypsyyden ja raskauden aikaisen sekä varhaisen postnataalisen kasvun välistä yhteyttä. Raskauden aikaisen kasvun vaikutusta tutkittiin käyttäen sekä ROI- että TBSS-tekniikoita. Postnataalista kasvua tarkasteltiin ainoastaan TBSS-tekniikalla. Tähän tutkimukseen otettiin mukaan keskoset, jotka syntyivät ennen 32 raskausviikkoa tai joiden syntymäpaino oli alle 1,501 g sekä MRI kuvaus oli tehty lasketunajan kohdalla. Tutkimukseen hyväksyttiin kesäkuun 2004 ja joulukuun 2006 välillä 132 keskosta. Poissulkukriteerien takia 76 keskosta (ROI) ja 36 (TBSS) hyväksyttiin tähän tutkimukseen. ROI-analyysi osoittautui melko toistettavaksi lasketun ajan iässä. Toistettavuus vaihteli sekä valkoisen aineen rakenteiden että diffuusioparametrien välillä. Normaali raskauden aikainen kasvu liittyi hyvään valkoisen aineen kehitykseen lasketunajan kohdalla. ROI-tekniikalla yhteys havaittiin corpus callosumin alueella. TBSS-menetelmä puolestaan näytti yhteyden usealla eri valkoisen aineen alueella. Syntymähetken gestaatioiällä ei havaittu yhteyttä valkoisen aineen kehitysasteeseen lasketun ajan kohdalla. Hyvän varhaisen vaiheen postnataalisen kasvun havaittiin liittyvän heikompaan valkoisen aineen kehitysasteeseen lasketunajan kohdalla. Saavutuskasvu ei ollut korjannut raskauden aikaisen kasvuhäiriön vaikutusta aivojen kypsyyteen laskettuun aikaan mennessä.Siirretty Doriast

    PRETERM BIRTH RESULTS IN ALTERATIONS IN NEURAL CONNECTIVITY AT AGE 16 YEARS

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    Very low birth weight preterm (PT) children are at high risk for brain injury. This study investigates microstructural differences in the brains of PT adolescents relative to term control subjects using diffusion tensor imaging (DTI), as well as studying their neurodevelopmental outcomes. Forty-four PT subjects (600 - 1250 grams birth weight) without neonatal brain injury and 41 term controls were evaluated at age 16 years with DTI, the Wechsler Intelligence Scale for Children - III (WISC), the Peabody Picture Vocabulary Test - Revised (PPVT), and the Comprehensive Test of Phonological Processing (CTOPP). PT subjects scored lower than term subjects on WISC full scale (p = 0.002), verbal (p = 0.027), and performance IQ tests (p = 0.001), as well as CTOPP phonological awareness (p = 0.005), but scored comparably to term subjects on PPVT and CTOPP Rapid Naming tests. PT subjects had lower fractional anisotropy (FA) values, suggestive of white matter disorganization, in multiple regions including bilateral uncinate fasciculi (left: p = 0.004; right: p = 0.002), bilateral external capsules (left: p \u3c 0.0001; right: p = 0.001), the splenium of the corpus callosum (p = 0.014), and white matter serving the inferior frontal gyrus bilaterally (left: p \u3c 0.0001; right: p = 0.005). FA values in both the left and right uncinate fasciculi correlated with PPVT scores (a semantic language task) in the PT subjects (left: R = 0.314, p = 0.038; right: R = 0.336, p = 0.026). FA values in the left and right arcuate fasciculi correlated with CTOPP Rapid Naming scores (a phonologic task) in the PT subjects (left: R = 0.424, p = 0.004; right: R = 0.301, p = 0.047). These data support for the first time that the recently proposed concept of dual pathways underlying language function are present in PT adolescents. These include a left-sided dorsal pathway associated with phonological and articulatory processing (arcuate fasciculus), and a bilateral ventral pathway for semantic, receptive language processing (uncinate fasciculus). The striking bilateral dorsal correlations for the PT group suggest that prematurely born subjects rely more heavily on the right hemisphere than typically developing adolescents for performance of phonological language tasks. These findings may represent either a delay in maturation or the engagement of alternative neural pathways for language in the developing PT brain

    Early postnatal development of corpus callosum and corticospinal white matter assessed with quantitative tractography

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    pre-printBACKGROUND AND PURPOSE: The early postnatal period is perhaps the most dynamic phase of white matter development. We hypothesized that the early postnatal development of the corpus callosum and corticospinal tracts could be studied in unsedated healthy neonates by using novel approaches to diffusion tensor imaging (DTI) and quantitative tractography. MATERIALS AND METHODS: Isotropic 2 x 2 x 2 mm3 DTI and structural images were acquired from 47 healthy neonates. DTI and structural images were coregistered and fractional anisotropy (FA), mean diffusivity (MD), and normalized T1-weighted (T1W) and T2-weighted (T2W) signal intensities were determined in central midline and peripheral cortical regions of the white matter tracts of the genu and splenium of the corpus callosum and the central midbrain and peripheral cortical regions of the corticospinal tracts by using quantitative tractography. RESULTS: We observed that central regions exhibited lower MD, higher FA values, higher T1W intensity, and lower T2W intensity than peripheral cortical regions. As expected, MD decreased, FA increased, and T2W signal intensity decreased with increasing age in the genu and corticospinal tract, whereas there was no significant change in T1W signal intensity. The central midline region of the splenium fiber tract has a unique pattern, with no change in MD, FA, or T2W signal intensity with age, suggesting different growth trajectory compared with the other tracts. FA seems to be more dependent on tract organization, whereas MD seems to be more sensitive to myelination. CONCLUSIONS: Our novel approach may detect small regional differences and age-related changes in the corpus callosum and corticospinal white matter tracts in unsedated healthy neonates and may be used for future studies of pediatric brain disorders that affect developing white matter

    Multimodality evaluation of the pediatric brain: DTI and its competitors

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    The development of the human brain, from the fetal period until childhood, happens in a series of intertwined neurogenetical and histogenetical events that are influenced by environment. Neuronal proliferation and migration, cell aggregation, axonal ingrowth and outgrowth, dendritic arborisation, synaptic pruning and myelinisation contribute to the ‘plasticity of the developing brain'. These events taken together contribute to the establishment of adult-like neuroarchitecture required for normal brain function. With the advances in technology today, mostly due to the development of non-invasive neuroimaging tools, it is possible to analyze these structural events not only in anatomical space but also longitudinally in time. In this review we have highlighted current ‘state of the art' neuroimaging tools. Development of the new MRI acquisition sequences (DTI, CHARMED and phase imaging) provides valuable insight into the changes of the microstructural environment of the cortex and white matter. Development of MRI imaging tools dedicated for analysis of the acquired images (i) TBSS and ROI fiber tractography, (ii) new tissue segmentation techniques and (iii) morphometric analysis of the cortical mantle (cortical thickness and convolutions) allows the researchers to map the longitudinal changes in the macrostructure of the developing brain that go hand-in-hand with the acquisition of cognitive skills during childhood. Finally, the latest and the newest technologies, like connectom analysis and resting state fMRI connectivity analysis, today, for the first time provide the opportunity to study the developing brain through the prism of maturation of the systems and networks beyond individual anatomical areas. Combining these methods in the future and modeling the hierarchical organization of the brain might ultimately help to understand the mechanisms underlying complex brain structure function relationships of normal development and of developmental disorder

    Cerebello-cerebral connectivity in the developing brain

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    Disrupted cerebellar development and injury is associated with impairments in both motor and non-motor domains. Methods to non-invasively characterize cerebellar afferent and efferent connections during early development are lacking. The aim of this study was to assess the feasibility of delineating cortico-ponto-cerebellar (CPC) and cerebello-thalamo-cortical (CTC) white matter tracts during brain development using high angular resolution diffusion imaging (HARDI). HARDI data were obtained in 24 infants born between 24+6 and 39 weeks gestational age (median 33+4 weeks) and scanned between 29+1 and 44 weeks postmenstrual age (PMA) (median 37+1 weeks). Probabilistic tractography of CPC and CTC fibers was performed using constrained spherical deconvolution. Connections between cerebellum and contralateral cerebral hemisphere were identified in all infants studied. Fractional anisotropy (FA) values of CTC and CPC pathways increased with increasing PMA at scan (p < 0.001). The supratentorial regions connecting to contralateral cerebellum in most subjects, irrespective of PMA at scan, included the precentral cortex, superior frontal cortex, supplementary motor area, insula, postcentral cortex, precuneus, and paracentral lobule. This study demonstrates the feasibility of assessing CTC and CPC white matter connectivity in vivo during the early stages of development. The ability to assess cerebellar connectivity during this critical developmental period may help improve our understanding of the role of the cerebellum in a wide range of neuromotor and neurocognitive disorders

    Fractional anisotropy in white matter tracts of very-low-birth-weight infants

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    Background: Advances in neonatal intensive care have not yet reduced the high incidence of neurodevelopmental disability among very-low-birth-weight (VLBW) infants. As neurological deficits are related to white-matter injury, early detection is important. Diffusion tensor imaging (DTI) could be an excellent tool for assessment of white-matter injury. Objective: To provide DTI fractional anisotropy (FA) reference values for white-matter tracts of VLBW infants for clinical use. Materials and methods: We retrospectively analysed DTI images of 28 VLBW infants (26-32 weeks gestational age) without evidence of white-matter abnormalities on conventional MRI sequences, and normal developmental outcome (assessed at age 1-3 years). For DTI an echoplanar sequence with diffusion gradient (b = 1,000 s/mm2) applied in 25 non-collinear directions was used. We measured FA and apparent diffusion coefficient (ADC) of different white-matter tracts in the first 4 days of life. Results: A statistically significant correlation was found between gestational age and FA of the posterior limb of the internal capsule in VLBW infants (r = 0.495, P<0.01). Conclusion: Values of FA and ADC were measured in white-matter tracts of VLBW infants. FA of the pyramidal tracts measured in the first few days after birth is related to gestational age

    Diffusion magnetic resonance imaging assessment of regional white matter maturation in preterm neonates

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    PURPOSE: Diffusion 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. METHODS: Thirty-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. RESULTS: PMA 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.). CONCLUSION: We 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

    Data quality in diffusion tensor imaging studies of the preterm brain: a systematic review

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    Background: To study early neurodevelopment in preterm infants, evaluation of brain maturation and injury is increasingly performed using diffusion tensor imaging, for which the reliability of underlying data is paramount. Objective: To review the literature to eva
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