Thesis defense Jeroen Mollink (Donders series 381)

25 June 2019

Promotors: prof. dr. L.T. Kozicz, prof. dr. K.L. Miller (University of Oxford, UK)
Co-promotors: dr. A.M. van Cappellen van Walsum, dr. M. Kleinnijenhuis (University of Oxford, UK)

Multiscale imaging of white matter microstructure

To address the title of this thesis – Multiscale imaging of white matter microstructure – we can think of the brain at various scales. Length scales range from the microscale at the level of individual neurons up to the macroscale where large white matter bundles connect distant brain areas with each other. Diffusion MRI is spanning a large fraction of these length scales. It is not able to image individual neurons, but it does provide microscopic sensitivity to features much smaller than the imaging resolution. Using microscopy, we aimed to ameliorate the interpretation of diffusion MRI at the microscale. A very different kind of scale is that of study size, which can range from individuals to populations. Both ends at the scales of people are important in different contexts; ultrahigh-resolution microscopy is generally limited to individuals due manual labour involved, but provides exquisite detail of the brain. At the other end, by studying populations we can establish normative descriptions that enables us to classify individuals (e.g., outliers may identify who is at risk for a disease). MRI is very suitable for studying populations, once standardized acquisition – and processing-protocols have been established. Having MRI data from a large cohort, we can make inferences from, for example microstructure and study its effect on brain function, lifestyle, behaviour, disease, aging or genetics. Throughout this thesis, we adopt this multiscale approach by combining microscopy with dMRI (spatial scale) and studying large amounts data from participants in the UK Biobank (population scale).