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

Abstract

Background and Purpose Artifact from cochlear implant electrodes degrades image resolution on CT. Here, we describe the use of coregistered pre‐ and postoperative CT images to reduce metallic artifact from the electrodes to assess its position more accurately within the cochlear lumen. Methods Pre‐ and postoperative CTs were reviewed after coregistration/overlay of both exams. Images were evaluated by two neuroradiologists for scalar location of electrodes tip (± scalar translocation), tip fold over, and angular depth of insertion. Results Thirty‐four patients were included in the final cohort. Transscalar migration was present in three (8.8%) cases (one case demonstrated tip fold over), with initial disagreement regarding transscalar migration in 1 out of 34 patients (2.9%). Agreement regarding depth of insertion was present in 31 (91.1%) cases. Five‐point Likert scales were used to compare the ability to resolve the proximity of electrodes to the lateral/outer cochlear wall without and with overlay, which is a qualitative measure of artifact from the array. Likert scores showed definitive benefit of metal artifact reduction using overlayed images with an average score of 4.34. Conclusion This study demonstrates a novel technique of using fused coregistration of pre‐ and postoperative CTs for the purpose of artifact reduction/electrode localization. It is anticipated that this technique will permit more accurate localization of the electrodes for improvement in surgical technique and electrode array design.

Evaluation of a Radiological Tool for Semiautomatic Scalar Translocation Detection After Cochlear Implantation

“…For scalar translocation detection of the complete electrode array, Jia et al (29) reported agreement between expert judgments on intraoperative cone beam CT to be as low as 43 to 53%. Farnsworth et al (13) found Cohen's κ of 0.78 for translocation agreement between experts in a relatively small study with three translocations in 34 patients. This means that differences between manual and semiautomatic scalar position assessments in our study are not necessarily errors from the tools, but could also be due to interobserver variability.…”

“…Because the contacts of a lateral wall array are located further away from the modiolar axis, a certain absolute localization difference will lead to a smaller difference in AID compared with precurved arrays. For example, one study found an interobserver ICC of 0.96 for manual AID measurement of straight arrays (28), whereas another found an ICC of 0.67 for patients implanted with a precurved array (13). Our results show that the tool leads to consistent AID measurements that are comparable to manual measurements.…”

“…The criterion standard for diagnosis of scalar translocation is histopathology, but because this is not possible in vivo, computed tomography (CT) is considered the criterion standard in a clinical setting, using either conventional CT or cone beam CT (8). However, manual determination of scalar translocation from CT is time-consuming and prone to intraobserver and interobserver variability (13,14). Therefore, (semi)automatic analysis of CT images would be a preferred method for detection of scalar translocation from CT images, with the added benefit of being able to provide more detailed information than manual determination.…”