Assessing Quantitative MRI Techniques using Multimodal Comparisons

The study of brain change in neuroscience studies is commonly conducted using macroscopic morphological measures of the brain such as regional volume or cortical thickness, providing little insight into the microscopic mechanisms underlying brain disease. In contrast, quantitative MRI allows the monitoring of microscopic brain change non-invasively in-vivo, and provides normative values for comparisons between tissues, regions, and individuals. To support the development and common use of qMRI for cognitive neuroscience, we analysed a set of qMRI metrics (R1, R2*, Magnetization Transfer saturation, Proton Density saturation, Fractional Anisotropy, Mean Diffusivity) in 101 healthy young adults. Here we provide a comprehensive descriptive analysis of these metrics and their linear relationships to each other in grey and white matter to develop a more complete understanding of the relationship to tissue microstructure. Furthermore, we provide evidence that combinations of metrics may uncover informative microstructural cortical gradients across the brain by showing that dimensionality reduction through PCA provides cortical gradients that were hidden in individual metrics. We discuss these results and their links to microstructural and physiological neuroscience research. ### Competing Interest Statement The authors have declared no competing interest.