OptTTA:
Learnable Test-Time Augmentation for Source-Free Medical Image Segmentation Under Domain Shift

Devavrat Tomar      Guillaume Vray      Jean-Philippe Thiran      Behzad Bozorgtabar
EPFL
CIBM
UNIL
CHUV
paper | code
MIDL 2022 (Oral)


Abstract

As distribution shifts are inescapable in realistic clinical scenarios due to inconsistencies in imaging protocols, scanner vendors, and across different centers, well-trained deep models incur a domain generalization problem in unseen environments. Despite a myriad of model generalization techniques to circumvent this issue, their broad applicability is impeded as (i) source training data may not be accessible after deployment due to privacy regulations, (ii) the availability of adequate test domain samples is often impractical, and (iii) such model generalization methods are not well-calibrated, often making unreliable overconfident predictions. This paper proposes a novel learnable test-time augmentation, namely OptTTA, tailored specifically to alleviate large domain shifts for the source-free medical image segmentation task. OptTTA enables efficiently generating augmented views of test input, resembling the style of private source images and bridging a domain gap between training and test data. Our proposed method explores optimal learnable test-time augmentation sub-policies that provide lower predictive entropy and match the feature statistics stored in the BatchNorm layers of the pretrained source model without requiring access to training source samples. Thorough evaluation and ablation studies on challenging multi-center and multi-vendor MRI datasets of three anatomies have demonstrated the performance superiority of OptTTA over prior-arts test-time augmentation and model adaptation methods. Additionally, the generalization capabilities and effectiveness of OptTTA are evaluated in terms of aleatoric uncertainty and model calibration analyses.


OptTTA Results

Below, we show related plots for the evolution of the top sub-policy on sample test images per dataset, reliability diagrams for pixel-wise predictions, and a comparison of the segmentation confidence and uncertainty of OptTTA against other test-time augmentation baselines on the Prostate dataset, respectively.


Try our code

We released PyTorch code and pre-trained models of the OptTTA for your use.

[GitHub]


Paper

D. Tomar, G. Vray, J.P. Thiran, B. Bozorgtabar
OptTTA: Learnable Test-Time Augmentation for Source-Free Medical Image Segmentation Under Domain Shift.
In MIDL, 2022 (Oral). OpenReview

BibTeX

@inproceedings{tomar2021opttta,
  title={OptTTA: Learnable Test-Time Augmentation for Source-Free Medical Image Segmentation Under Domain Shift},
  author={Tomar, Devavrat and Vray, Guillaume and Thiran, Jean-Philippe and Bozorgtabar, Behzad},
  booktitle={Medical Imaging with Deep Learning (MIDL)},
  year={2022}
}



Acknowledgements

We thank Taesung Park for his project page template.