Interobserver regional variability of left ventricular endocardium and epicardium delineation in echocardiography imaging
Authors: Garcia-Mato D , Giraldo Del Viejo E , Berto A , Garcia-Sineriz I , Garcia-Elcano L , Diez-Lopez C , Cabrera J A , Bossa M N , Corral Acero J 
Published: January 2025

Abstract

Introduction
Accurate delineation of the left ventricle (LV) endocardium and epicardium remains a significant challenge in echocardiography due to low image quality and tissue contrast, leading to a compromised reproducibility of LV border tracing [1]. Whereas the global variability in echocardiography segmentation is extensively discussed in the literature [2], there is still a substantial gap in understanding the distribution of border delineation error across the different regions of LV.

Purpose
This study aims to extensively analyse discrepancies in the echocardiography delineation of LV endocardial and epicardial borders at global and regional levels by considering a large cohort of annotation experts.

Methods
LV endocardial and epicardial borders were independently delineated by 35 sonographers from multiple institutions in apical 4-chamber (A4C) and 2-chamber (A2C) echocardiography sequences at end-diastole (ED) and end-systole (ES) in a cohort of 10 patients, totalling 80 annotations per observer. The ES and ED frames were preselected, and their ground truth was determined by a clinical committee. LV sections were obtained via standard Simpson’s rule [3], yielding 82 reference points along the epicardium and endocardium, grouped into 4 regions (septal, lateral, anterior, inferior) across 3 levels (basal, mid, apical) plus the apex, resulting in 13 segments. Global segmentation error was quantified using the Dice Similarity Coefficient (DSC) and Hausdorff 95% distance (HD95). Regional error was estimated as the minimum Euclidean distance from each of the 82 ground truth reference points to the segmentation border, averaged across LV segments and patients. Statistical significance was assessed via paired t-test.

Results
The average DSC was 0.87±0.03 and 0.92±0.02, and the average HD95 was 6.0±1.4 and 5.8±1.1 mm for endocardium and epicardium, respectively (Figure 1). Segmentation error was significantly lower at ED compared to ES (p=0.003) and in A4C compared to A2C (p=0.001). In line with the latter, the error in the septal region was significantly the lowest (Figure 2). A positive error trend base-to-apex is observed, with the error significantly the smallest at the basal level. Errors were more prominent in the apical lateral endocardial segment in A4C and in the apical anterior segment in A2C. These errors can be explained by the higher LV curvature in these segments [4]. Epicardium apex error could have been slightly underestimated due to some of the contours falling outside of the field of view in this region.

Conclusion
This work introduces a reproducible method to analyse global and regional variability in LV border tracing in echocardiography. The study identifies compromised segments that can be targeted via enhanced training and standardised protocols to effectively reduce interobserver variability, leading to consistent and accurate interpretations, ultimately benefiting patient care.