Addressing multi‐site functional MRI heterogeneity through dual‐expert collaborative learning for brain disease identification

Several studies employ multi‐site rs‐fMRI data for major depressive disorder (MDD) identification, with a specific site as the to‐be‐analyzed target domain and other site(s) as the source domain. But they usually suffer from significant inter‐site heterogeneity caused by the use of different scanners and/or scanning protocols and fail to build generalizable models that can well adapt to multiple target domains. In this article, we propose a dual‐expert fMRI harmonization (DFH) framework for automated MDD diagnosis. Our DFH is designed to simultaneously exploit data from a single labeled source domain/site and two unlabeled target domains for mitigating data distribution differences across domains. Specifically, the DFH consists of a domain‐generic student model and two domain‐specific teacher/expert models that are jointly trained to perform knowledge distillation through a deep collaborative learning module. A student model with strong generalizability is finally derived, which can be well adapted to unseen target domains and analysis of other brain diseases. To the best of our knowledge, this is among the first attempts to investigate multi‐target fMRI harmonization for MDD diagnosis. Comprehensive experiments on 836 subjects with rs‐fMRI data from 3 different sites show the superiority of our method. The discriminative brain functional connectivities identified by our method could be regarded as potential biomarkers for fMRI‐related MDD diagnosis.