Objectives: The need to intraoperatively confirm correct placement of the active electrode of a cochlear implant may occur in various clinical settings. These include a malformed cochlea, difficulty with insertion, or suboptimal or abnormal electrical responses (impedance or evoked action potentials) obtained during intraoperative testing. Frustration with inconsistent images using portable x-ray machines prompted this study to determine the technique needed to reliably image the electrode within the cochlea. Our objective was to establish a radiology protocol that would be reproducible and reliable across institutions.
Methods: Prospective cadaveric imaging study. Access to the round window via the facial recess was established using cadaver heads. Electrodes provided by three cochlear implant manufacturers were inserted into the cochlea. The position of the head, angle of the x-ray tube, and beam settings were varied. A compendium of electrode images was obtained and analyzed by neurotologists and a head and neck radiologist to reach a consensus on an optimal imaging protocol.
Results: The optimal position for intraoperative x-ray confirmation of cochlear implant electrode placement is obtained by turning the head 45 degrees toward the contralateral ear. The portable digital x-ray machine and central ray was angled 15 degrees (aiming cephalic) from vertical with exposure settings of 32 mAs at 70 kVp and the digital radiography image receptor was positioned under the mattress of the operating table.
Conclusion: A protocol for patient and beam source positioning and exposure using a portable digital x-ray unit can provide reliable imaging for intraoperative confirmation of cochlear implant electrode positioning.