Learning to quantify emphysema extent: What labels do we need?

TL;DR

This study investigates machine learning methods to accurately quantify emphysema extent from CT scans, comparing models trained on presence versus extent labels, and finds that presence labels suffice for high performance.

Contribution

The paper demonstrates that learning from emphysema presence labels can achieve comparable accuracy to learning from extent labels, simplifying data annotation.

Findings

Models trained on presence labels achieve correlation coefficients around 0.90.

Performance with presence labels is comparable to extent labels, with agreement rates of 78-79%.

Inter-rater agreement among human raters is 83%.

Abstract

Accurate assessment of pulmonary emphysema is crucial to assess disease severity and subtype, to monitor disease progression and to predict lung cancer risk. However, visual assessment is time-consuming and subject to substantial inter-rater variability and standard densitometry approaches to quantify emphysema remain inferior to visual scoring. We explore if machine learning methods that learn from a large dataset of visually assessed CT scans can provide accurate estimates of emphysema extent. We further investigate if machine learning algorithms that learn from a scoring of emphysema extent can outperform algorithms that learn only from a scoring of emphysema presence. We compare four Multiple Instance Learning classifiers that are trained on emphysema presence labels, and five Learning with Label Proportions classifiers that are trained on emphysema extent labels. We evaluate performance on 600 low-dose CT scans from the Danish Lung Cancer Screening Trial and find that learning from emphysema presence labels, which are much easier to obtain, gives equally good performance to learning from emphysema extent labels. The best classifiers achieve intra-class correlation coefficients around 0.90 and average overall agreement with raters of 78% and 79% on six emphysema extent classes versus inter-rater agreement of 83%.