From preoperative computed tomography to postmastoidectomy mesh construction: mastoidectomy shape prediction for cochlear implant surgery.

Abstract

Purpose: Cochlear implant (CI) surgery treats severe hearing loss by inserting an electrode array into the cochlea to stimulate the auditory nerve. An important step in this procedure is mastoidectomy, which removes part of the mastoid region of the temporal bone to provide surgical access. Accurate mastoidectomy shape prediction from preoperative imaging improves presurgical planning, reduces risks, and enhances surgical outcomes. Despite its importance, there are limited deep-learning-based studies regarding this topic due to the challenges of acquiring ground-truth labels. We address this gap by investigating self-supervised and weakly-supervised learning models to predict the mastoidectomy region without human annotations.

Approach: We propose a hybrid self-supervised and weakly-supervised learning framework to predict the mastoidectomy region directly from preoperative CT scans, where the mastoid remains intact. Our self-supervised learning approach reconstructs the postmastoidectomy 3D surface from preoperative imaging, aiming to align with the corresponding intraoperative microscope views for future surgical navigation-related applications. Postoperative CT scans are used in the self-supervised learning model to assist training procedures despite additional challenges such as metal artifacts and low signal-to-noise ratios introduced by them. To further improve the accuracy and robustness, we introduce a Mamba-based weakly-supervised model that refines mastoidectomy shape prediction by using 3D T-distribution loss function, inspired by the student- $t$ distribution. Weak supervision is achieved by leveraging segmentation results from the prior self-supervised framework, eliminating the manual data labeling process.

Results: Our hybrid method achieves a mean Dice score of 0.72 when predicting the complex and boundary-less mastoidectomy shape, surpassing state-of-the-art approaches and demonstrating strong performance. The method provides groundwork for constructing 3D postmastoidectomy surfaces directly from the corresponding preoperative CT scans.

Conclusion: To our knowledge, this is the first work that integrates self-supervised and weakly-supervised learning for mastoidectomy shape prediction, offering a robust and efficient solution for CI surgical planning while leveraging 3D T-distribution loss in weakly-supervised medical imaging.