In the early 2000s, several ambitious studies built cohorts numbering thousands of subjects. Several recent brain imaging studies are aiming to image tens of thousands of subjects, including the Maastricht Study (n=10,000)49, the German National Cohort (n=30,000)50 and the Rhineland Study (n=30,000). In addition to having even larger numbers, UK Biobank will benefit from the breadth of organ systems imaged, the highly multi-modal brain protocol, and the existing rich phenotyping. A longitudinal component is planned for a subset of the UK Biobank imaging participants (n=10,000), as in the Rhineland and GNC studies. Most of these studies use identical MRI scanners at a small number of dedicated sites, with the goal of maximizing data homogeneity within study. A future challenge to further leveraging these large datasets is to develop analysis tools that can harmonize data across these studies for combined analyses, where there could be considerable impact in focusing on harmonization of a few very large cohorts.
