Verification of computed tomographic estimates of cochlear implant array position: a micro-CT and histologic analysis

Abstract

Objective: To determine the efficacy of clinical computed tomographic (CT) imaging to verify postoperative electrode array placement in cochlear implant (CI) patients.

Study design: Nine fresh cadaver heads underwent clinical CT scanning, followed by bilateral CI insertion and postoperative clinical CT scanning. Temporal bones were removed, trimmed, and scanned using micro-CT. Specimens were then dehydrated, embedded in either methyl methacrylate or LR White resin, and sectioned with a diamond wafering saw. Histology sections were examined by 3 blinded observers to determine the position of individual electrodes relative to soft tissue structures within the cochlea. Electrodes were judged to be within the scala tympani, scala vestibuli, or in an intermediate position between scalae.

Results: The position of the array could be estimated accurately from clinical CT scans in all specimens using micro-CT and histology as a criterion standard. Verification using micro-CT yielded 97% agreement, and histologic analysis revealed 95% agreement with clinical CT results.

Conclusion: A composite, 3-dimensional image derived from a patient's preoperative and postoperative CT images using a clinical scanner accurately estimates the position of the electrode array as determined by micro-CT imaging and histologic analyses. Information obtained using the CT method provides valuable insight into numerous variables of interest to patient performance such as surgical technique, array design, and processor programming and troubleshooting.

FIG. 1

Clinical CT method. Our clinical method to determine the position of electrodes is illustrated. A preoperative CT scan is combined with the postoperative scan with the electrode array in place, allowing accurate registration without interference from blooming artifact. A 3-dimensional reconstruction is made, referencing to an atlas made from a cochlea sectioned by OPFOS, allowing the scalar position of each electrode to be determined.

FIG. 2

Verification methods. Clinical CT (top) and micro-CT (bottom) through the same section of the temporal bone with the implant in place.

FIG. 3

Verification methods. Histologic section (top) and micro-CT image (bottom) through the same section of the temporal bone. Micro-CT scan reformatted to match the section of the histologic slice.

FIG. 4

Correlation of micro-CT, histology, and clinical CT. We tabulated the position of each part of the electrode array in the histologic sections and depicted them with arrowheads in this figure. The position of each electrode was determined by clinical CT scanning and depicted them with circles. The position of each is shown as depicted in the figure.

FIG. 5

The 3 possible positions of the electrode array are depicted: within the SV (A), in an intermediate position (in this instance, displacing the basilar membrane apically) (B), and within the ST (C).