Co-Registration of pre- and post-Operative images after cochlear Implantation: A proposed technique to Improve cochlear visualization and localization of cochlear electrodes

Abstract

Background and Purpose After cochlear implantation, metallic artifact can obscure nearby structures on CT images, which is problematic in patients with facial nerve stimulation (FNS). This study evaluated the usefulness of co-registered pre- and post-operative examinations to evaluate the cochlear implant and adjacent structures. Materials and Methods A retrospective review was completed of consecutive patients that underwent CT imaging of the temporal bone before and after placement of a cochlear implant. Two blinded neuroradiologists independently reviewed all available examinations. All examinations were assessed for the presence or absence of dehiscence of the osseous ridge between the cochlea and facial nerve canal (FNC). Pre-operative and fused pre- and post-operative examinations were compared in their ability to visualize the osseous ridge using a 5-point Likert scale (ranging from 1 = unfused images were substantially superior to 5 = fused images were substantially superior). The electrode closest to the FNC were noted. Results Of 34 included patients, 13 (38.2%) were female and 21 (61.8%) were male; average age was 72.2. Seven patients (20.6%) had frank dehiscence between the cochlea and FNC. Fused images were superior to the post-operative study alone for assessing the integrity of the osseous partition between the cochlea and FNC and for reducing artifact from the electrode array (average Likert scores for both reviewers were 4.4 and 4.7). There was good agreement between reviewers in noting electrode closest to the FNC (concordance correlation coefficient=0.82). Conclusions Following cochlear implantation, co-registered pre- and post-operative CT images are superior to conventional images in assessing the anatomic relationship between the cochlea and FNC.

Postoperative Impedance-Based Estimation of Cochlear Implant Electrode Insertion Depth

“…For preoperative cochlear landmark and postoperative electrode contact labeling, the open-source software 3D Slicer ( Fedorov et al 2012 ) was used. The postoperative CT scans were co-registered to the preoperative CT scans using a rigid transform and mutual information metric ( Klein et al 2009 ) to reduce landmark labeling errors that could result from electrode array artifacts ( Benson et al 2022 ). Subsequently, we measured the cochlear base length and width ( Rathgeb et al 2019 ) and labeled the electrodes using maximum intensity projection.…”

“…array artifacts (Benson et al 2022). Subsequently, we measured the cochlear base length and width (Rathgeb et al 2019) and labeled the electrodes using maximum intensity projection.…”

Improved cochlear implant electrode localization using coregistration of pre‐ and postoperative CT

“…This method of coregistration for artifact reduction has been previously described by Benson et al. for use in assessing the anatomic relationship between the cochlea and facial nerve canal, 6 which is unique from our study that is artifact reduction for localization of the CI electrodes. Prior articles have also discussed some main alternative methods for artifact reduction in CI evaluation, such as fusion of preoperative MRI with postoperative MDCT, 8,9 fusion of preoperative MRI with postoperative CBCT, 10 CBCT/DVT alone, 11 and MDCT/HRCT alone 12 .…”

“…Benson et al previously described this method for artifact reduction; however, this was to assess the anatomic relationship between the cochlea and the facial nerve canal. 6 Skinner et al previously described the use of coregistration of pre-and postoperative temporal bone CT images for evaluating CI implant position; however, they used ANALYZE software with a very different, more timeintensive methodology that will be further discussed later. 7 Additional previously described methods for artifact reduction include fusion of preoperative MRI with postoperative MDCT, 8,9 fusion of preoperative MRI with postoperative cone beam CT (CBCT), 10 CBCT/digital volume tomography (DVT) alone, 11 and MDCT alone.…”

“…Benson et al. previously described this method for artifact reduction; however, this was to assess the anatomic relationship between the cochlea and the facial nerve canal 6 . Skinner et al.…”