SSEGEP: Small SEGment Emphasized Performance evaluation metric for medical image segmentation

TL;DR

This paper introduces SSEGEP, a new evaluation metric for medical image segmentation that emphasizes smaller segments, improving accuracy in detecting clinically significant small regions across various medical imaging datasets.

Contribution

The paper proposes SSEGEP, a novel segmentation performance metric that assigns higher importance to smaller segments, addressing limitations of traditional metrics like DSC.

Findings

SSEGEP is 30% closer to expert opinion scores than DSC.

Statistical tests show significant improvement with SSEGEP (p-value ~10^{-18}).

SSEGEP performs better on images with multiple segments for a single label.

Abstract

Automatic image segmentation is a critical component of medical image analysis, and hence quantifying segmentation performance is crucial. Challenges in medical image segmentation are mainly due to spatial variations of regions to be segmented and imbalance in distribution of classes. Commonly used metrics treat all detected pixels, indiscriminately. However, pixels in smaller segments must be treated differently from pixels in larger segments, as detection of smaller ones aid in early treatment of associated disease and are also easier to miss. To address this, we propose a novel evaluation metric for segmentation performance, emphasizing smaller segments, by assigning higher weightage to smaller segment pixels. Weighted false positives are also considered in deriving the new metric named, "SSEGEP"(Small SEGment Emphasized Performance evaluation metric), (range : 0(Bad) to 1(Good)). The experiments were performed on diverse anatomies(eye, liver, pancreas and breast) from publicly available datasets to show applicability of the proposed metric across different imaging techniques. Mean opinion score (MOS) and statistical significance testing is used to quantify the relevance of proposed approach. Across 33 fundus images, where the largest exudate is 1.41%, and the smallest is 0.0002% of the image, the proposed metric is 30% closer to MOS, as compared to Dice Similarity Coefficient (DSC). Statistical significance testing resulted in promising p-value of order 10^{-18} with SSEGEP for hepatic tumor compared to DSC. The proposed metric is found to perform better for the images having multiple segments for a single label.