Learning Generalized Medical Image Representation by Decoupled Feature Queries.

Medical images are usually collected from multiple clinical centers with various types of scanners. When confronted with such significant cross-domain distribution discrepancy, a deep network tends to capture similar patterns by multiple channels, while different cross-domain patterns are also allowed to rest in the same channel. Such channel redundancy limits the expressive capability of a representation, resulting in less preferable generalization ability. To address this fundamental yet challenging issue, we propose a novel decoupled feature as query (DFQ) framework for domain generalized medical image representation learning. Its general idea is to leverage the channel-wise decoupled deep features as queries. Particularly, a deep instance whitening transform with restricted isometry is proposed, which enforces each channel orthogonal to the rest channels after decoupling. Besides, the long-range dependency between decoupled deep and shallow features is implicitly constrained to minimize channel redundancy throughout training. Extensive experiments show its state-of-the-art performance on three medical domain generalization tasks with four modalities.