@article{KossenHirzelMadaietal., author = {Kossen, Tabea and Hirzel, Manuel A. and Madai, Vince I. and Boenisch, Franziska and Hennemuth, Anja and Hildebrand, Kristian and Pokutta, Sebastian and Sharma, Kartikey and Hilbert, Adam and Sobesky, Jan and Galinovic, Ivana and Khalil, Ahmed A. and Fiebach, Jochen B. and Frey, Dietmar}, title = {Towards Sharing Brain Images: Differentially Private TOF-MRA Images with Segmentation Labels Using Generative Adversarial Networks}, series = {Frontiers in Artificial Intelligence}, journal = {Frontiers in Artificial Intelligence}, doi = {https://doi.org/10.3389/frai.2022.813842}, abstract = {Sharing labeled data is crucial to acquire large datasets for various Deep Learning applications. In medical imaging, this is often not feasible due to privacy regulations. Whereas anonymization would be a solution, standard techniques have been shown to be partially reversible. Here, synthetic data using a Generative Adversarial Network (GAN) with differential privacy guarantees could be a solution to ensure the patient's privacy while maintaining the predictive properties of the data. In this study, we implemented a Wasserstein GAN (WGAN) with and without differential privacy guarantees to generate privacy-preserving labeled Time-of-Flight Magnetic Resonance Angiography (TOF-MRA) image patches for brain vessel segmentation. The synthesized image-label pairs were used to train a U-net which was evaluated in terms of the segmentation performance on real patient images from two different datasets. Additionally, the Fr{\´e}chet Inception Distance (FID) was calculated between the generated images and the real images to assess their similarity. During the evaluation using the U-Net and the FID, we explored the effect of different levels of privacy which was represented by the parameter ϵ. With stricter privacy guarantees, the segmentation performance and the similarity to the real patient images in terms of FID decreased. Our best segmentation model, trained on synthetic and private data, achieved a Dice Similarity Coefficient (DSC) of 0.75 for ϵ = 7.4 compared to 0.84 for ϵ = ∞ in a brain vessel segmentation paradigm (DSC of 0.69 and 0.88 on the second test set, respectively). We identified a threshold of ϵ <5 for which the performance (DSC <0.61) became unstable and not usable. Our synthesized labeled TOF-MRA images with strict privacy guarantees retained predictive properties necessary for segmenting the brain vessels. Although further research is warranted regarding generalizability to other imaging modalities and performance improvement, our results mark an encouraging first step for privacy-preserving data sharing in medical imaging.}, language = {en} } @article{NohadaniSharma, author = {Nohadani, Omid and Sharma, Kartikey}, title = {Optimization under Connected Uncertainty}, series = {INFORMS Journal on Optimization}, volume = {4}, journal = {INFORMS Journal on Optimization}, number = {3}, doi = {10.1287/ijoo.2021.0067}, pages = {326 -- 346}, abstract = {Robust optimization methods have shown practical advantages in a wide range of decision-making applications under uncertainty. Recently, their efficacy has been extended to multiperiod settings. Current approaches model uncertainty either independent of the past or in an implicit fashion by budgeting the aggregate uncertainty. In many applications, however, past realizations directly influence future uncertainties. For this class of problems, we develop a modeling framework that explicitly incorporates this dependence via connected uncertainty sets, whose parameters at each period depend on previous uncertainty realizations. To find optimal here-and-now solutions, we reformulate robust and distributionally robust constraints for popular set structures and demonstrate this modeling framework numerically on broadly applicable knapsack and portfolio-optimization problems.}, language = {en} } @article{KevinMartinBaermannBraunetal., author = {Kevin-Martin, Aigner and B{\"a}rmann, Andreas and Braun, Kristin and Liers, Frauke and Pokutta, Sebastian and Schneider, Oskar and Sharma, Kartikey and Tschuppik, Sebastian}, title = {Data-driven Distributionally Robust Optimization over Time}, series = {INFORMS Journal on Optimization}, volume = {5}, journal = {INFORMS Journal on Optimization}, number = {4}, doi = {10.1287/ijoo.2023.0091}, pages = {376 -- 394}, abstract = {Stochastic optimization (SO) is a classical approach for optimization under uncertainty that typically requires knowledge about the probability distribution of uncertain parameters. Because the latter is often unknown, distributionally robust optimization (DRO) provides a strong alternative that determines the best guaranteed solution over a set of distributions (ambiguity set). In this work, we present an approach for DRO over time that uses online learning and scenario observations arriving as a data stream to learn more about the uncertainty. Our robust solutions adapt over time and reduce the cost of protection with shrinking ambiguity. For various kinds of ambiguity sets, the robust solutions converge to the SO solution. Our algorithm achieves the optimization and learning goals without solving the DRO problem exactly at any step. We also provide a regret bound for the quality of the online strategy that converges at a rate of O(log T/T--√), where T is the number of iterations. Furthermore, we illustrate the effectiveness of our procedure by numerical experiments on mixed-integer optimization instances from popular benchmark libraries and give practical examples stemming from telecommunications and routing. Our algorithm is able to solve the DRO over time problem significantly faster than standard reformulations.}, language = {en} } @article{KruserSharmaHolletal., author = {Kruser, Jacqueline M. and Sharma, Kartikey and Holl, Jane L. and Nohadani, Omid}, title = {Identifying Patterns of Medical Intervention in Acute Respiratory Failure: A Retrospective Observational Study}, series = {Critical Care Explorations}, volume = {5}, journal = {Critical Care Explorations}, number = {10}, doi = {10.1097/CCE.0000000000000984}, pages = {p e0984}, language = {en} } @inproceedings{SharmaHendrychBesanconetal., author = {Sharma, Kartikey and Hendrych, Deborah and Besan{\c{c}}on, Mathieu and Pokutta, Sebastian}, title = {Network Design for the Traffic Assignment Problem with Mixed-Integer Frank-Wolfe}, series = {Proceedings of INFORMS Optimization Society Conference}, booktitle = {Proceedings of INFORMS Optimization Society Conference}, language = {en} } @inproceedings{WaeldchenSharmaTuranetal., author = {W{\"a}ldchen, Stephan and Sharma, Kartikey and Turan, Berkant and Zimmer, Max and Pokutta, Sebastian}, title = {Interpretability Guarantees with Merlin-Arthur Classifiers}, series = {Proceedings of International Conference on Artificial Intelligence and Statistics}, booktitle = {Proceedings of International Conference on Artificial Intelligence and Statistics}, abstract = {We propose an interactive multi-agent classifier that provides provable interpretability guarantees even for complex agents such as neural networks. These guarantees consist of lower bounds on the mutual information between selected features and the classification decision. Our results are inspired by the Merlin-Arthur protocol from Interactive Proof Systems and express these bounds in terms of measurable metrics such as soundness and completeness. Compared to existing interactive setups, we rely neither on optimal agents nor on the assumption that features are distributed independently. Instead, we use the relative strength of the agents as well as the new concept of Asymmetric Feature Correlation which captures the precise kind of correlations that make interpretability guarantees difficult. We evaluate our results on two small-scale datasets where high mutual information can be verified explicitly.}, language = {en} }