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Lung cancer is the leading cause of cancer death worldwide, and adenocarcinoma (LUAD) is the most common subtype. Exploiting the potential value of the histopathology images can promote precision medicine in oncology. Tissue segmentation is the basic upstream task of histopathology image analysis. Existing deep learning models have achieved superior segmentation performance but require sufficient pixel-level annotations, which is time-consuming and expensive. To enrich the label resources of LUAD and to alleviate the annotation efforts, we organize this challenge WSSS4LUAD to call for the outstanding weakly-supervised semantic segmentation (WSSS) techniques for histopathology images of LUAD. Participants have to design the algorithm to segment tumor epithelial, tumor-associated stroma and normal tissue with only patch-level labels. This challenge includes 10,091 patch-level annotations (the training set) and over 130 million labeled pixels (the validation and test sets), from 87 WSIs (67 from GDPH, 20 from TCGA). All the labels were generated by a pathologist-in-the-loop pipeline with the help of AI models and checked by the label review board. Among 532 registrations, 28 teams submitted the results in the test phase with over 1,000 submissions. Finally, the first place team achieved mIoU of 0.8413 (tumor: 0.8389, stroma: 0.7931, normal: 0.8919). According to the technical reports of the top-tier teams, CAM is still the most popular approach in WSSS. Cutmix data augmentation has been widely adopted to generate more reliable samples. With the success of this challenge, we believe that WSSS approaches with patch-level annotations can be a complement to the traditional pixel annotations while reducing the annotation efforts. The entire dataset has been released to encourage more researches on computational pathology in LUAD and more novel WSSS techniques.

Tissue-level semantic segmentation is a vital step in computational pathology. Fully-supervised models have already achieved outstanding performance with dense pixel-level annotations. However, drawing such labels on the giga-pixel whole slide images is extremely expensive and time-consuming. In this paper, we use only patch-level classification labels to achieve tissue semantic segmentation on histopathology images, finally reducing the annotation efforts. We proposed a two-step model including a classification and a segmentation phases. In the classification phase, we proposed a CAM-based model to generate pseudo masks by patch-level labels. In the segmentation phase, we achieved tissue semantic segmentation by our proposed Multi-Layer Pseudo-Supervision. Several technical novelties have been proposed to reduce the information gap between pixel-level and patch-level annotations. As a part of this paper, we introduced a new weakly-supervised semantic segmentation (WSSS) dataset for lung adenocarcinoma (LUAD-HistoSeg). We conducted several experiments to evaluate our proposed model on two datasets. Our proposed model outperforms two state-of-the-art WSSS approaches. Note that we can achieve comparable quantitative and qualitative results with the fully-supervised model, with only around a 2\% gap for MIoU and FwIoU. By comparing with manual labeling, our model can greatly save the annotation time from hours to minutes. The source code is available at: \url{https://github.com/ChuHan89/WSSS-Tissue}., Comment: 15 pages, 10 figures, journal

In this paper, two kinds of occurrence mechanism on the phenomenon of concentration and the formation of delta shock waves are analyzed and identified in the flux approximation limit of Riemann solutions to the extended Chaplygin gas equations with Coulomb-like friction, whose special case can also be seen as the model of the magnetogasdynamics with Coulomb-like friction. Firstly, by introducing a transformation, the Riemann problem for the extended Chaplygin gas equations with Coulomb-like friction is solved completely. Secondly, we rigorously show that, as the pressure vanishes, any two-shock Riemann solution to the nonhomogeneous extended Chaplygin gas equations tends to a {\delta}-shock solution to the corresponding nonhomogeneous transportation equations, and the intermediate density between the two shocks tends to a weighted {\delta}-measure that forms the {\delta}-shock; any two-rarefaction-wave Riemann solution to the nonhomogeneous extended Chaplygin gas equations tends to a two-contact-discontinuity solution to the correspongding nonhomogeneous transportation equations, and the nonvacuum intermediate state between the two rarefaction waves tends to a vacuum state. At last, we also show that, as the pressure approaches the generalized Chaplygin pressure, any two-shock Riemann solution to the nonhomogeneous extended Chaplygin gas equations tends to a delta-shock solution to the correspongding nonhomogeneous generalized Chaplygin gas equations. In a word, we have generalized all the results about the vanishing pressure limit now available for homogeneous equations to the nonhomogeneous case., Comment: arXiv admin note: substantial text overlap with arXiv:1707.05153

In this paper, the Riemann problem for the pressureless Euler equations with a discontinuous source term is considered. The delta shock wave solution is obtained by combining the generalized Rankine-Hugoniot conditions together with the method of characteristics for different situations, which reflects the impact of the source term on the delta shock front. Moreover, during the construction process of the Riemann solution, some interesting phenomena are also observed, such as the disappearance of the delta shock wave and the occurrence of the vacuum state, etc.

In this paper, two kinds of occurrence mechanism on the phenomenon of concentration and the formation of delta shock wave in the flux approximation limit of Riemann solutions to the extended Chaplygin gas equations are analyzed and identified. Firstly, the Riemann problem of the extended Chaplygin gas equations is solved completely. Secondly, we rigorously show that, as the pressure vanishes, any two-shock Riemann solution to the extended Chaplygin gas equations tends to a $\delta$-shock solution to the transport equations, and the intermediate density between the two shocks tends to a weighted $\delta$-measure that forms the $\delta$-shock; any two-rarefaction-wave Riemann solution to the extended Chaplygin gas equations tends to a two-contact-discontinuity solution to the transport equations, and the nonvacuum intermediate state between the two rarefaction waves tends to a vacuum state. At last, we also show that, as the pressure approaches the generalized Chaplygin pressure, any two-shock Riemann solution tends to a delta-shock solution to the generalized Chaplygin gas equations., Comment: arXiv admin note: text overlap with arXiv:1503.08382 by other author

We study the stability of Riemann solutions to pressureless Euler equations with Coulomb-like friction under the nonlinear approximation of flux functions with one parameter. The approximated system can be seen as the generalized Chaplygin pressure Aw-Rascle model with Coulomb-like friction, which is also equivalent to the nonsymmetric system of Keyfitz-Kranzer type with generalized Chaplygin pressure and Coulomb-like friction. Compared with the original system, The approximated system is strictly hyperbolic, which has one eigenvalue genuinely nonlinear and the other linearly degenerate. Hence, the structure of its Riemann solutions is much different from the ones of the original system. However, it is proven that the Riemann solutions for the approximated system converge to the corresponding ones to the original system as the perturbation parameter tends to zero, which shows that the Riemann solutions to nonhomogeneous pressureless Euler equations is stable under such kind of flux approximation. The result in this paper generalizes the stability of Riemann solutions with respect to flux perturbation from the well-known homogeneous case to the nonhomogeneous case., Comment: arXiv admin note: substantial text overlap with arXiv:1612.08533

The Riemann solution to the Chaplygin pressure Aw-Rascle model with Coulomb-like friction is constructed explicitly and its vanishing pressure limit is analyzed precisely. It is shown that the delta shock wave appears in the Riemann solutions in some certain situations. The generalized Rankine-Hugoniot conditions of the delta shock wave are established and the exact position, propagation speed and strength of the delta shock wave are given explicitly, which enables us to see the influence of the Coulomb-like friction on the Riemann solution to the Chaplygin pressure Aw-Rascle model clearly. It is shown that the Coulomb-like friction term makes contact discontinuities and delta shock waves bend into parabolic shapes and the Riemann solutions are not self-similar anymore. Finally, the occurrence mechanism on the phenomenon of concentration and cavitation and the formation of delta shock wave and vacuum in the process of vanishing pressure limit are analyzed and identified in detail. Moreover, we show the Riemann solutions to the nonhomogeneous Chaplygin pressure Aw-Rascle model converge to the Riemann solutions to the transportation equations with the same source term as the pressure vanishes. These two results generalize those obtained in [7,38] for homogeneous equations to nonhomogeneous equations and are also applicable to the nonsymmetric system of Keyfitz-Kranzer type with the same Chaplygin pressure and Coulomb-like friction.