Shape-related characteristics of age-related differences in subcortical structures

ABSTRACT

Objectives: With an increasing aging population, it is important to understand biological markers of aging. Subcortical volume is known to differ with age; additionally considering shape-related characteristics may provide a better index of age-related differences. Fractal dimensionality is more sensitive to age-related differences, but is borne out of mathematical principles, rather than neurobiological relevance. We considered four distinct measures of shape and how they relate to aging and fractal dimensionality: surface-to-volume ratio, sphericity, long-axis curvature, and surface texture.

Methods: Structural MRIs from a combined sample of over 600 healthy adults were used to measure age-related differences in the structure of the thalamus, putamen, caudate, and hippocampus. For each, volume and fractal dimensionality were calculated, as well as four distinct shape measures. These measures were examined for their utility in explaining age-related variability in brain structure.

Results: The four shape measures were able to account for 80%–90% of the variance in fractal dimensionality. Of the distinct shape measures, surface-to-volume ratio was the most sensitive biomarker.

Conclusion: Though volume is often used to characterize inter-individual differences in subcortical structures, our results demonstrate that additional measures can be useful complements. Our results indicate that shape characteristics are useful biological markers of aging.

KEYWORDS:

• Structural MRI
• brain morphology
• fractal dimensionality
• volume
• thalamus
• caudate
• radiomics

Acknowledgments

I would like to thank Elizabeth Kensinger for feedback on an earlier version of the manuscript.

MRI data used in the preparation of this article were obtained from several sources, data were provided in part by: (1) the Open Access Series of Imaging Studies (OASIS; Marcus et al., 2007); and (2) wave 1 of the Dallas Lifespan Brain Study (DLBS) led by Dr. Denise Park, and distributed through INDI (Mennes et al., 2013) and NITRC (Kennedy et al., 2016).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by a fellowship from the Canadian Institutes of Health Research [grant number FRN-146793].