Class imbalance is a critical challenge in medical image classification, particularly in gastroscopy, where accurately detecting underrepresented pathological conditions is essential for clinical decision-making. This paper investigates algorithm-level techniques’ effectiveness in addressing severe class imbalance in gastroscopy image classification. A curated data set comprising four clinically relevant categories was constructed: normal, esophagitis, Barrett’s esophagus, and gastric polyps by consolidating and reclassifying samples from two open-access sources: the HyperKvasir and GastroVision datasets. The resulting dataset exhibits a pronounced imbalance ratio of approximately \( \rho \approx 73 \) , closely reflecting real-world diagnostic scenarios. To mitigate the adverse effects of imbalance, we evaluate the performance of two algorithm-level methods: Focal Loss and a cost-sensitive learning strategy (CoSen). These methods were integrated into deep learning pipelines based on a convolutional neural network and transformer architectures. Experimental results demonstrate that both approaches substantially improve the F1-score, particularly for the minority polyp class. The best model achieved a 40.4% increase in F1 score for one class compared to the baseline, underscoring the value of algorithmic imbalance mitigation strategies for gastrocopy image classification.

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Classification of Gastroscopy Images Under Extreme Class Imbalance: A Deep Learning Pipeline

  • Adrian Krenzer,
  • Tobias Friedetzki,
  • Max Dietsch,
  • Frank Puppe

摘要

Class imbalance is a critical challenge in medical image classification, particularly in gastroscopy, where accurately detecting underrepresented pathological conditions is essential for clinical decision-making. This paper investigates algorithm-level techniques’ effectiveness in addressing severe class imbalance in gastroscopy image classification. A curated data set comprising four clinically relevant categories was constructed: normal, esophagitis, Barrett’s esophagus, and gastric polyps by consolidating and reclassifying samples from two open-access sources: the HyperKvasir and GastroVision datasets. The resulting dataset exhibits a pronounced imbalance ratio of approximately \( \rho \approx 73 \) , closely reflecting real-world diagnostic scenarios. To mitigate the adverse effects of imbalance, we evaluate the performance of two algorithm-level methods: Focal Loss and a cost-sensitive learning strategy (CoSen). These methods were integrated into deep learning pipelines based on a convolutional neural network and transformer architectures. Experimental results demonstrate that both approaches substantially improve the F1-score, particularly for the minority polyp class. The best model achieved a 40.4% increase in F1 score for one class compared to the baseline, underscoring the value of algorithmic imbalance mitigation strategies for gastrocopy image classification.