Poster E12, Thursday, August 22, 2019, 3:45 – 5:30 pm, Restaurant Hall
Investigating white matter tissue properties in dyslexia: A combined analysis of DTI and myelin water imaging
Maria Economou1, Thanh Vân Phan1,2, Thibo Billiet2, Jolijn Vanderauwera3, Jan Wouters1, Pol Ghesquière3, Maaike Vandermosten1;1Experimental Oto-rhino-laryngology, Department of Neurosciences, KU Leuven, 2icometrix, Research and Development, Leuven, 3Parenting and Special Education Research Unit, Faculty of Psychology and Educational Sciences, KU Leuven
Structural organization of white matter (WM) plays a crucial role in the development of the reading network. Previous research has revealed WM differences in dyslexic individuals, mainly in left temporo-parietal connections. These findings were recently extended to pre-reading children, emphasizing the role of early white matter organization on the development of reading trajectories. Although the use of diffusion MRI (dMRI) has been invaluable in this domain, it does not provide sufficient information to characterize tissue-specific properties. This is primarily because dMRI indices such as fractional anisotropy (FA) are sensitive, but not specific to several tissue changes including myelination and axonal growth. In this study, we aim to address this limitation by combining information from dMRI as well as myelin water imaging (MWI), to elucidate the potential specific contribution of myelin. MWI allows the quantification of myelin water fraction (MWF) in the brain, an index that can be used as a proxy for myelin content. We hypothesize that combining MWF with typical diffusion indices such as FA will be more informative than FA alone. We tested this on a group of 69 children (9-10 years old) of whom 27 were dyslexics. All children underwent an MRI session (at 3T using a 32-channel coil) as well as a behavioral assessment, where various reading-related and perception skills were tested. The MWI dataset was acquired using a 3D GraSE sequence. Using the non-negative least squares algorithm to derive values per voxel, MWF parameter maps were calculated. The DWI dataset was acquired using a b-value of 1300 s/mm2, 60 non-collinear directions, and 6 non-diffusion-weighted images. Following appropriate pre-processing and corrections, the tensor model was fitted to the data and whole-brain tractography was conducted, followed by manual delineations of bilateral white matter tracts. We chose to focus on the direct segment of the arcuate fasciculus (AF) and the inferior fronto-occipital fasciculus (IFOF) given their previous implication in the reading network. Preliminary results revealed no significant group differences in neither FA nor MWF in dyslexic readers compared to their peers. Post-hoc correlations showed some weak associations between vocabulary scores and WM metrics in the left IFOF of typical readers (FA: rs=0.453, p=0.018; MWF: rs=0.395, p=0.041), which however did not survive appropriate testing corrections. This lack of significant findings could suggest that if group differences in white matter FA are observed in dyslexics, these are less likely to be driven by myelination. Nevertheless, given the dynamic changes in myelination in early development, this conclusion cannot be made with certainty from the present sample. Overall, we describe a novel multi-modal approach to characterize WM in children with (a)typical reading ability. Although we were unable to replicate previous WM findings in dyslexics, the analysis employed here and the use of MWI is an important contribution to understanding the neurobiological basis of typical and atypical reading. We aim to extend our analyses by looking at how different reading growth profiles might relate to MWF, and how this integrated approach can be used to study WM organization prior to reading onset.
Themes: Disorders: Developmental, Reading
Method: White Matter Imaging (dMRI, DSI, DKI)