Boundary Distance Loss for Intra-/Extra-meatal Segmentation of Vestibular Schwannoma

TL;DR

This paper introduces a two-stage MRI segmentation method for Vestibular Schwannoma, utilizing a novel Boundary Distance Loss to improve intra-/extra-meatal boundary accuracy, achieving significant performance gains over baseline models.

Contribution

The study proposes a new Boundary Distance Loss and a two-stage segmentation approach for better delineation of intra-/extra-meatal regions in Vestibular Schwannoma from MRI data.

Findings

Achieved higher Dice scores for intra-/extra-meatal segmentation compared to baseline.

Boundary Distance Loss significantly improves boundary accuracy.

Two-stage approach enhances overall segmentation performance.

Abstract

Vestibular Schwannoma (VS) typically grows from the inner ear to the brain. It can be separated into two regions, intrameatal and extrameatal respectively corresponding to being inside or outside the inner ear canal. The growth of the extrameatal regions is a key factor that determines the disease management followed by the clinicians. In this work, a VS segmentation approach with subdivision into intra-/extra-meatal parts is presented. We annotated a dataset consisting of 227 T2 MRI instances, acquired longitudinally on 137 patients, excluding post-operative instances. We propose a staged approach, with the first stage performing the whole tumour segmentation and the second stage performing the intra-/extra-meatal segmentation using the T2 MRI along with the mask obtained from the first stage. To improve on the accuracy of the predicted meatal boundary, we introduce a task-specific loss which we call Boundary Distance Loss. The performance is evaluated in contrast to the direct intrameatal extrameatal segmentation task performance, i.e. the Baseline. Our proposed method, with the two-stage approach and the Boundary Distance Loss, achieved a Dice score of 0.8279+-0.2050 and 0.7744+-0.1352 for extrameatal and intrameatal regions respectively, significantly improving over the Baseline, which gave Dice score of 0.7939+-0.2325 and 0.7475+-0.1346 for the extrameatal and intrameatal regions respectively.