1Image Sciences Institute, University Medical Center Utrecht, Utrecht, The Netherlands; 2Department of Otorhinolaryngology and Head & Neck Surgery, University Medical Center Utrecht, Utrecht, The Netherlands; 3Brain Center Rudolf Magnus, University Medical Center Utrecht, Utrecht, The Netherlands; and 4Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands.
Ear Hear. 2017 Nov/Dec;38(6):e376-e384. doi: 10.1097/AUD.0000000000000438.
Determining the exact location of cochlear implant (CI) electrode contacts after implantation is important, as it helps quantifying the relation between CI positioning and hearing outcome. Unfortunately, localization of individual contacts can be difficult, because the spacing between the electrode contacts is near the spatial resolution limit of high-resolution clinical computed tomography (CT) scanners. This study introduces and examines a simple, automatic method for the localization of intracochlear electrode contacts. CI geometric specifications may provide the prior knowledge that is essential to accurately estimate contact positions, even though individual contacts may not be visibly resolved.
The prior knowledge in CI geometry is used to accurately estimate intracochlear electrode contact positions in high-resolution CT scans of seven adult patients implanted with a CI (Cochlear Ltd.). The automatically detected electrode contact locations were verified against locations marked by two experienced observers. The interobserver errors and the errors between the averaged locations and the automatically detected locations were calculated. The estimated contact positions were transformed to a cylindrical cochlear coordinate system, according to an international consensus, in which the insertion angles and the radius and elevation were measured.
The linear correlation of the automatically detected electrode contact positions with the manually detected locations was high (R = 0.98 for the radius, and R = 1.00 for the insertion angle). The errors in radius and in insertion angle between the automatically detected locations and the manually detected locations were 0.12 mm and 1.7°. These errors were comparable to the interobserver errors. Geometrical measurements were in line with what is usually found in human cochleae. The mean insertion angle of the most apical electrode was 410° (range: 316° to 503°). The mean radius of the electrode contacts in the first turn of the cochlear spiral was 3.0 mm, and the mean radius of the remainder in the second turn was 1.7 mm.
With implant geometry as prior knowledge, automatic analysis of high-resolution CT scans enables accurate localization of CI electrode contacts. The output of this method can be used to study the effect of CI positioning on hearing outcomes in more detail.
确定植入后耳蜗植入物（CI）电极触点的确切位置很重要，因为它有助于量化 CI 定位与听力结果之间的关系。不幸的是，由于电极触点之间的间距接近高分辨率临床计算机断层扫描（CT）扫描仪的空间分辨率极限，因此单个触点的定位可能很困难。本研究介绍并检验了一种用于定位耳蜗内电极触点的简单、自动方法。CI 的几何规格可以提供先验知识，即使个别触点无法清晰分辨，这对于准确估计触点位置也是必不可少的。
在对 7 名植入 CI（Cochlear Ltd.）的成年患者的高分辨率 CT 扫描中，使用 CI 几何形状的先验知识来准确估计耳蜗内电极触点的位置。自动检测到的电极触点位置与两位经验丰富的观察者标记的位置进行了验证。计算了观察者间误差和平均位置与自动检测位置之间的误差。根据国际共识，将估计的触点位置转换到圆柱耳蜗坐标系中，其中测量插入角度和半径以及高程。
自动检测到的电极触点位置与手动检测到的位置之间的线性相关性很高（半径的 R = 0.98，插入角度的 R = 1.00）。自动检测位置与手动检测位置之间的半径和插入角度误差分别为 0.12mm 和 1.7°。这些误差与观察者间误差相当。几何测量与通常在人耳蜗中发现的一致。最顶点电极的平均插入角度为 410°（范围：316°至 503°）。耳蜗螺旋第一圈电极触点的平均半径为 3.0mm，第二圈其余部分的平均半径为 1.7mm。
利用植入物的几何形状作为先验知识，对高分辨率 CT 扫描进行自动分析可以实现 CI 电极触点的精确定位。该方法的输出可用于更详细地研究 CI 定位对听力结果的影响。
