Practicable Assessment of Cochlear Size and Shape from Clinical CT Images

Abstract

There is considerable interpersonal variation in the size and shape of the human cochlea, with evident consequences for cochlear implantation. The ability to characterize a specific cochlea, from pre-operative computed tomography (CT) images, would allow the clinician to personalize the choice of electrode, surgical approach and post-operative programming. In this study, we present a fast, practicable and freely available method for estimating cochlear size and shape from clinical CT. The approach taken is to fit a template surface to the CT data, using either a statistical shape model (SSM) or a locally affine deformation (LAD). After fitting, we measure cochlear length, mean lumen area and a novel measure of basal turn non-planarity, which is expected to correlate with the risk of insertion trauma. Gold-standard measurements from a convenience sample of 18 micro-CT scans are compared with the same quantities estimated from low resolution, noisy, pseudo-clinical data synthesized from the same micro-CT scans. The results show that the LAD method outperforms the SSM method, with an expected error of around 11% of the gold-standard sample range for non-planarity and cochlear length. Results for lumen area are significantly worse, reflecting the difficulty of detecting the cochlear inner wall in clinical CT.