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Automatic Quantification of COVID-19 Pulmonary Edema by Self-supervised Contrastive Learning
Zhaohui Liang1, Zhiyun Xue1, Sivaramakrishnan Rajaraman1
1Computational Health Research Branch, National Library of Medicine, National Institutes of Health, Bethesda, MD, USA.
Summary
A new self-supervised machine learning model accurately rates pulmonary edema severity on chest X-rays using the mRALE score. This AI approach shows superior performance compared to traditional methods, aiding in COVID-19 pneumonia assessment.
Area of Science:
- Artificial Intelligence
- Medical Imaging
- Machine Learning
Background:
- Pulmonary edema assessment on chest X-rays (CXR) is crucial for diagnosing conditions like COVID-19 pneumonia.
- Automated scoring systems can improve efficiency and consistency in evaluating lung edema severity.
Purpose of the Study:
- To develop and evaluate a self-supervised machine learning method for automated pulmonary edema severity rating using the modified radiographic assessment of lung edema (mRALE) scoring system on frontal CXRs.
- To compare the performance of the proposed model against non-pretrained and from-scratch trained comparators.
Main Methods:
- A self-supervised contrastive learning approach utilizing a Siamese network (SimSiam) architecture with a pre-trained ResNet-50 backbone was employed.
- The model generated 2048-dimension embeddings for a downstream deep neural network to predict mRALE scores.
- Performance was evaluated using 5-fold cross-validation on 2,599 frontal CXRs and external validation.
Main Results:
- The proposed model achieved superior performance with a mean absolute error (MAE) of 5.05, mean squared error (MSE) of 66.67, and Spearman's correlation coefficient (Spearman ρ) of 0.77 compared to comparators (P<0.01).
- External validation demonstrated a prediction probability concordance of 0.811 and quadratic weighted kappa of 0.739.
- Comparator models showed no statistically significant difference in MSE and Spearman ρ (P>0.05).
Conclusions:
- Self-supervised contrastive learning is an effective strategy for automated mRALE scoring.
- The developed method offers a novel approach to enhance machine learning performance in quantitative medical image analysis.
- This technique minimizes the need for extensive expert knowledge in learning patterns from medical images.

