Söderqvist Samuel, Sivonen Ville, Huber Alexander, Sinkkonen Saku T, Sijgers Leanne
Department of Otorhinolaryngology - Head and Neck Surgery and Tauno Palva Laboratory, Head and Neck Center, Helsinki University Hospital and University of Helsinki, Helsinki, Finland; Department of Otorhinolaryngology - Head and Neck Surgery, Turku University Hospital, Turku, Finland.
Department of Otorhinolaryngology - Head and Neck Surgery and Tauno Palva Laboratory, Head and Neck Center, Helsinki University Hospital and University of Helsinki, Helsinki, Finland.
Hear Res. 2025 Aug 4;466:109382. doi: 10.1016/j.heares.2025.109382.
Stimulation of cochlear implant electrodes generates intracochlear electric potentials. The local electric potentials can be assessed using e.g. transimpedance matrix (TIM) and four-point impedance (Z). Both of these measurements are dependent on the cochlear dimensions and the distance between the electrode and the medial wall of the scala tympani (d). In a recent temporal bone study, a model based on electric potential measurements gave good predictions of scalar cross-sectional area (A) and d. The purpose of this study was to further improve this model and evaluate its clinical usefulness. To this end, the intraoperative TIM and Z measurements from cochlear implant patients were used as independent variables in the model to predict their A and d at each electrode contact, which were then compared to those measured from postoperative cone-beam computed tomography (CBCT) images.
In an earlier study, six cadaveric temporal bones were sequentially implanted with three different electrode arrays: a lateral-wall electrode array, Slim Straight, and two precurved perimodiolar electrode arrays, Contour Advance and Slim Modiolar (Cochlear Ltd, Sydney, Australia). The TIM and Z measurements were performed alongside CBCT imaging, from which the A and d at each electrode contact were measured. From the TIM measurements, the peak amplitudes and decay rate of the electric potentials (EP) were computed. In this follow-up study, the statistical modeling of the ex vivo measurements was refined to better account for individual characteristics by employing mixed-effect models to predict the As and ds. Then, in vivo recordings from thirteen patients, of which six were implanted with the Slim Straight and seven with the Contour Advance electrode arrays, were retrospectively analyzed. The As and ds were measured from their postoperative CBCT images in a similar manner to the temporal bones. To validate the mixed-effects models developed with the temporal bone data, the patients' intraoperative TIM and Z measurements were used as independent parameters in the models to predict their As and ds. Finally, the TIM and Z parameters measured in vivo and ex vivo and the measured and predicted As and ds were compared using t-tests. Also, Pearson's correlation coefficients were computed between the measured and predicted in vivo As and ds.
Both the amplitudes, indicating electric potential peaks, and Zs, reflecting local potential differences, were lower in vivo than ex vivo (790 vs. 1090 Ω and 253 vs. 270 Ω, respectively, p < 0.001 for both), but no differences were detected in the decay of the electric potentials. In addition, the in vivo Zs were lower, and the electric potential decay was slower with the lateral wall (Slim Straight) compared to perimodiolar (Contour Advance) array (234 vs. 284 Ω and -94 vs. -160 Ω/mm, p < 0.001 for both). The mixed effects models with and without random effects explained 73 % and 51 % of the variance, respectively, for A. The mean absolute error between measured and predicted As was 12 %. For ds, the corresponding percentages were 65 %, 50 %, and 51 %. The correlations between the patients' measured and predicted As and ds were r = 0.60 and r = 0.48 (p < 0.001, for both). When compared in the basal, middle, and apical sections, the predicted As differed significantly from the measured values only in the middle section of the array (4.0 ± 0.48 mm vs 3.50 ± 0.36 mm, p < 0.001). For ds, the model gave too large estimates in the apical section of the array (1.04 ± 0.49 mm vs. 1.52 ± 0.48, p < 0.001).
The A at each electrode contact can be estimated using the TIM and Z measurements, which may help verify the correct alignment of the electrode array during the surgery. While the measured and predicted ds correlated with each other, there were significant differences between their absolute values. Given the large variation in ds for different array types, electrode-specific ds models could improve the accuracy of the predictions.
人工耳蜗电极的刺激会产生耳蜗内电势。局部电势可通过例如跨阻抗矩阵（TIM）和四点阻抗（Z）进行评估。这两种测量都取决于耳蜗尺寸以及电极与鼓阶内侧壁之间的距离（d）。在最近的一项颞骨研究中，基于电势测量的模型对标量横截面积（A）和d给出了良好的预测。本研究的目的是进一步改进该模型并评估其临床实用性。为此，将人工耳蜗植入患者术中的TIM和Z测量值用作模型中的自变量，以预测每个电极触点处的A和d，然后将其与术后锥形束计算机断层扫描（CBCT）图像测量值进行比较。
在早期研究中，对六个尸体颞骨依次植入三种不同的电极阵列：一个侧壁电极阵列Slim Straight，以及两个预弯曲的蜗轴周围电极阵列Contour Advance和Slim Modiolar（澳大利亚悉尼科利耳有限公司）。在进行CBCT成像的同时进行TIM和Z测量，从中测量每个电极触点处的A和d。根据TIM测量值，计算电势（EP）的峰值幅度和衰减率。在这项后续研究中，通过采用混合效应模型来更好地考虑个体特征，对离体测量的统计模型进行了改进，以预测A和d。然后，对13名患者的体内记录进行回顾性分析，其中6名植入了Slim Straight电极阵列，7名植入了Contour Advance电极阵列。以与颞骨类似的方式从他们的术后CBCT图像中测量A和d。为了验证利用颞骨数据开发的混合效应模型，将患者术中的TIM和Z测量值用作模型中的独立参数来预测他们的A和d。最后，使用t检验比较体内和离体测量的TIM和Z参数以及测量和预测的A和d。此外，计算体内测量和预测的A和d之间的Pearson相关系数。
体内的电势峰值幅度和反映局部电位差的Z值均低于离体值（分别为790 vs. 1090 Ω和253 vs. 270 Ω，两者p < 0.001），但电势衰减未检测到差异。此外，与蜗轴周围（Contour Advance）阵列相比，侧壁（Slim Straight）阵列的体内Z值更低，电势衰减更慢（234 vs. 284 Ω和 -94 vs. -160 Ω/mm，两者p < 0.001）。有随机效应和无随机效应的混合效应模型分别解释了A的73%和51%的方差。测量和预测的A之间的平均绝对误差为12%。对于d，相应的百分比分别为65%、50%和51%。患者测量和预测的A和d之间的相关性分别为r = 0.60和r = 0.48（两者p < 0.001）。在基底部、中部和顶部进行比较时，预测的A仅在阵列中部与测量值有显著差异（4.0 ± 0.48 mm vs 3.50 ± 0.36 mm，p < 0.001）。对于d，该模型在阵列顶部的估计值过大（1.04 ± 0.49 mm vs. 1.52 ± 0.48，p < 0.001）。
可使用TIM和Z测量来估计每个电极触点处的A，这可能有助于在手术期间验证电极阵列的正确对齐。虽然测量和预测的d相互相关，但其绝对值之间存在显著差异。鉴于不同阵列类型的d差异很大，特定电极的d模型可以提高预测的准确性。
