IN-VIVO MEASURES OF COCHLEAR LENGTH AND INSERTION DEPTH OF NUCLEUS COCHLEAR IMPLANT ELECTRODE ARRAYS

Three-dimensional cochlear canal lengths, electrode array intracochlea r insertion depths, and characteristic frequency ranges were estimated for 20 Nucleus implant recipients on the basis of in vivo computed to mography (CT) scans. Ultra-high resolution images were reconstructed f rom 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 arra y insertion depths estimated by 3-dimensional (3-D) spiral calculation s (mean 20.19 mm: SD 2.86) and by a computerized array tracking algori thm (mean 20.36 mm; SD 2.66) were not significantly different. Estimat es from surgical observations were significantly longer (mean 21.03 mm ; SD 2.31) because array compressions were not detectable. Characteris tic frequencies at apical electrodes estimated from Greenwood's equati ons ranged from 387 Hz to 2,596 Hz. The results show that significant variations in cochlear anatomy and array distribution among implant pa tients that may impact implant performance can be reliably detected an d quantified by using in vivo high-resolution CT and 3-D reconstructio ns.