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In vivo measures of cochlear length and insertion depth of nucleus cochlear implant electrode arrays.
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1998
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NeurotologyBiomedical EngineeringOrthopaedic SurgeryVivo MeasuresSocial SciencesSpiral CalculationsHearing AidsNucleus Implant RecipientsAuditory ScienceCochlear Implant CommunicationRadiologyHealth SciencesInsertion DepthMedical ImagingCochlear NucleiAudiologyAuditory ResearchHuman HearingApical ElectrodesHearing LossNeurophysiologyBioelectronicsCochlear Implant NeuroscienceCochlear PhysiologyAuditory PhysiologyElectrophysiologyNeuroscienceCochlear ImplantCochlear LengthCochlear Implantation
The study used ultra‑high‑resolution spiral CT scans with 0.1‑mm slices and expanded attenuation scales to reconstruct 3‑D cochlear canal lengths, electrode insertion depths, and characteristic frequency ranges via 3‑D spiral calculations, a computerized array‑tracking algorithm, and Greenwood’s equations. Canal lengths averaged 33.01 mm, matching normal temporal bone data, while electrode insertion depths averaged ~20.2 mm by 3‑D calculations and ~20.4 mm by tracking, with surgical observations overestimating depth by ~1 mm; these findings demonstrate that in‑vivo high‑resolution CT and 3‑D reconstructions reliably detect clinically relevant variations in cochlear anatomy and array placement that could affect implant performance.
Three-dimensional cochlear canal lengths, electrode array intracochlear insertion depths, and characteristic frequency ranges were estimated for 20 Nucleus implant recipients on the basis of in vivo computed tomography (CT) scans. Ultra-high resolution images were reconstructed from spiral CT data with 0.1-mm slicing and expanded attenuation scales. Canal length estimates (mean 33.01 mm; SD 2.31) were consistent with previous findings for normal human temporal bones. Intracochlear array insertion depths estimated by 3-dimensional (3-D) spiral calculations (mean 20.19 mm; SD 2.86) and by a computerized array tracking algorithm (mean 20.36 mm; SD 2.66) were not significantly different. Estimates from surgical observations were significantly longer (mean 21.03 mm; SD 2.31) because array compressions were not detectable. Characteristic frequencies at apical electrodes estimated from Greenwood's equations ranged from 387 Hz to 2,596 Hz. The results show that significant variations in cochlear anatomy and array distribution among implant patients that may impact implant performance can be reliably detected and quantified by using in vivo high-resolution CT and 3-D reconstructions.