![]() ![]() For example, for voxel-level analyses, this usually requires images to be registered to a common template space. The ComBat harmonization requires the imaging data to be represented in a matrix where rows are the imaging features (for instance voxels, ROIs or connectome edges) and columns are the participants. We recommend to use the ComBat harmonization method after imaging processing before downstream statistical analyses. We also showed that ComBat was robust to unbalanced studies, in which the biological covariate of interest is not balanced across sites. We showed that ComBat performs well for multi-site imaging studies that only have a few participants per site. In two recent papers ( harmonization of DTI data and harmonization of cortical thickness measurements) we have shown that ComBat, a popular batch-effect correction tool used in genomics, succesffuly removes inter-site technical variability while preserving inter-site biological variability. To maximize statistical power, post-processing data harmonization is a powerful technique to remove unwanted variation when combining data across scanners and sites. This includes common imaging modalities, such as MRI, fMRI and DTI, as well as measurements derived from those modalities, for instance ROI volumes, RAVENS maps, cortical thickness measurements, connectome matrices, etc. ![]() Imaging data suffer from technical between-scanner variation that hinders comparisons of images across imaging sites, scanners and over time. Evan Johnson and Cheng Li, Adjusting batch effects in microarray expression data using empirical Bayes methods. ![]() Original ComBat paper for gene expression array Harmonization of cortical thickness measurements across scanners and sites. Cook, Phil Adams, Crystal Cooper, Maurizio Fava, Patrick J. Jean-Philippe Fortin, Nicholas Cullen, Yvette I. NeuroImage, 161, 149-170, 2017ĬomBat for multi-site cortical thickness measurements Harmonization Of Multi-Site Diffusion Tensor Imaging Data. Jean-Philippe Fortin, Drew Parker, Birkan Tunc, Takanori Watanabe, Mark A Elliott, Kosha Ruparel, David R Roalf, Theodore D Satterthwaite, Ruben C Gur, Raquel E Gur, Robert T Schultz, Ragini Verma, Russell T Shinohara. References: If you are using ComBat for the harmonization of multi-site imaging data, please cite the following papers: Maintainer: Jean-Philippe Fortin, R code: Artistic 2.0 License ComBatHarmonization Harmonization of multi-site imaging data with ComBat ![]()
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