Cortical Depth Dependent Microstructural Variations in Aging using Diffusion Tensor Imaging
Poster No:
1177
Submission Type:
Abstract Submission
Authors:
Yutong Sun1, Jordan Chad2, J. Jean Chen1
Institutions:
1Medical Biophysics, University of Toronto, Toronto, Ontario, 2Rotman Research Institute, Baycrest Health Sciences, Toronto, Ontario
First Author:
Co-Author(s):
Introduction:
Although the utilization of diffusion-tensor imaging (DTI) in cortical gray matter (GM) is limited, previous findings have demonstrated an increased GM mean diffusivity (MD) and fractional anisotropy (FA) with aging1,2. However, their interpretations remain unclear. Since the cyto- and myelo-architecture vary along the cortical laminae3, we hypothesize that age effects in DTI parameters also vary across cortical layers. In this study, using a recently published approach6, we investigate the cortical depth dependence of DTI age effects.
Methods:
700 subjects were taken from the UK Biobank, with 100 subjects of balanced sex ratio in each quinquennial. Data were collected using a Skyra 3T scanner with 50x b=1000 and 50 2000s/mm2, voxel resolution=2mm3. We applied eddy-current and susceptibility-induced distortions using EDDY, as well as 3D gradient distortion correction. The b=1000 data was used to calculate MD. The norm of anisotropy (NA) was calculated using the orthogonal-tensor decomposition method to measure anisotropy without bias from MD5. For MD and NA, age effects (%change/year) were projected onto the FreeSurfer cortical surface. These were sampled between projfrac of 0.0 (representing the WM boundary) and 1.0 (representing the pial surface) at step of 0.1.
Results:
We found a positive association between MD and age across the cortex, and both positive and negative age-associations in NA.
Stronger MD-age effects on the pial surface (Fig. 1): This is true in most cortical regions, whereby for most regions showing a strong positive NA-age association, it was stronger on the pial surface. There was no such preference for the negative NA-age associations.
Stronger MD-age effects on the WM surface (Fig. 2): MD-age effects were stronger on the WM surface for the right entorhinal, right isthmus cingulate, as well as the parahippocampal gyrus. NA-age effects displayed different depth dependencies across hemispheres. For instance, the parahippocampal and left entorhinal regions showed a negative NA-age association stronger on the WM surface, whereas the negative association in the right entorhinal region was stronger on the pial surface. Lastly, a positive NA-age association was only found in the right but not the left isthmus cingulate, being stronger on the WM surface.
The few regions (e.g. left isthmus cingulate) without cortical depth dependence for MD-age associations also lacked it for NA-age associations.
Stronger MD-age effects on the pial surface (Fig. 1): This is true in most cortical regions, whereby for most regions showing a strong positive NA-age association, it was stronger on the pial surface. There was no such preference for the negative NA-age associations.
Stronger MD-age effects on the WM surface (Fig. 2): MD-age effects were stronger on the WM surface for the right entorhinal, right isthmus cingulate, as well as the parahippocampal gyrus. NA-age effects displayed different depth dependencies across hemispheres. For instance, the parahippocampal and left entorhinal regions showed a negative NA-age association stronger on the WM surface, whereas the negative association in the right entorhinal region was stronger on the pial surface. Lastly, a positive NA-age association was only found in the right but not the left isthmus cingulate, being stronger on the WM surface.
The few regions (e.g. left isthmus cingulate) without cortical depth dependence for MD-age associations also lacked it for NA-age associations.
Conclusions:
For the dominant trend of MD-age effects being positive and stronger on the pial surface, negative NA-age associations greater on the pial surface may suggest increasing partial-volume effects with cerebrospinal fluid (CSF), resulting from cortical atrophy (Fig.1a, b). Positive NA-age associations stronger on the pial surface may suggest selective degeneration of crossing fibres in the superficial cortical layers (Fig. 1c, d). Positive NA-age associations stronger on the WM surface may indicate the co-existence of cortical atrophy and selective degeneration of crossing fibres in the base cortical layers (Fig. 1e, f). Negative NA-age associations stronger at the WM surface may be driven by a co-existence of atrophy and demyelination in the base cortical layers (Fig. 1g, h).
With positive MD-age associations stronger on the WM boundary, a concurrent positive NA-age associations stronger on the WM surface (Fig. 2c, d) could suggest selective degeneration of crossing fibres in the base cortical layers. A negative NA-age association stronger at the pial surface (Fig. 2a, b) could suggest the tensor shape is becoming more isotropic but disproportionate to demyelination. Lastly, a negative NA-age association stronger on the WM boundary (Fig. 2b) could suggest demyelination potentially accompanied loss of WM packing density in the base cortical layers.
Stronger MD-age effects on the WM boundary versus the pial surface likely suggests different stages of degeneration.
With positive MD-age associations stronger on the WM boundary, a concurrent positive NA-age associations stronger on the WM surface (Fig. 2c, d) could suggest selective degeneration of crossing fibres in the base cortical layers. A negative NA-age association stronger at the pial surface (Fig. 2a, b) could suggest the tensor shape is becoming more isotropic but disproportionate to demyelination. Lastly, a negative NA-age association stronger on the WM boundary (Fig. 2b) could suggest demyelination potentially accompanied loss of WM packing density in the base cortical layers.
Stronger MD-age effects on the WM boundary versus the pial surface likely suggests different stages of degeneration.
Lifespan Development:
Aging 1
Neuroanatomy, Physiology, Metabolism and Neurotransmission:
Cortical Cyto- and Myeloarchitecture 2
Novel Imaging Acquisition Methods:
Diffusion MRI
Keywords:
Aging
Cortical Layers
1|2Indicates the priority used for review
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3. Zilles, K., Palomero-Gallagher, N., & Amunts, K. (2015). Cytoarchitecture and maps of the human cerebral cortex.
4. UK Biobank - UK Biobank. (2022) [cited 2022Nov6]. Available from: https://www.ukbiobank.ac.uk/
5. Chad, J. A., Pasternak, O., & Chen, J. J. (2021). Orthogonal moment diffusion tensor decomposition reveals age-related degeneration patterns in complex fiber architecture. Neurobiology of Aging, 101, 150-159.
6. Truong, T. K., Guidon, A., & Song, A. W. (2014). Cortical depth dependence of the diffusion anisotropy in the human cortical gray matter in vivo. PloS one, 9(3), e91424.