Artifacts of the electrode in cochlea implantation and limits in analysis of deep insertion in cone beam tomography (CBT)

Abstract

Until now more than 250,000 cochlea implantations have been performed worldwide. The surgical procedure is well standardized. A discussion about the kind of postoperative radiological control has started since cone beam tomography (CBT) has been established in ENT and hearing preservation operations have come more into the focus. Further research has been concentrated on the role of CBT and the insertion of the basal turn. The aim of this study was to look for the possibilities of CBT and deep insertion. The second aim was to analyze the artifacts of cochlea implants in CBT. Three human cadaver ears were implanted with a flex soft electrode of MedEl© in a standard operation procedure with round window insertion and a full insertion. Afterwards 72 CBT sets per ear were performed with different X-ray-tube currents (2-10 mA), voltages (72-90 kV), and exposure times (9 and 17 s). On each data set, the radiological diameter of the electrode 9 (basal), electrode 2 (apical), the diameter of the cable next to the electrodes 9 and 2, and the associated diameter of the cochlea next to the electrodes 9 and 2 were evaluated. Additionally, a comparison to the real diameter was done. The mean radiological diameters of the measure point at electrode 9 were: electrode = 1.19 mm; cable = 0.65 mm; cochlea = 1.77 mm. Results for measure point at electrode 2 were: electrode = 0.98 mm; cable = 0.48 mm; cochlea = 1.21 mm. The real diameters were at electrode 9 in lateral view 0.58 mm and in top view 0.63 mm and at electrode 2 in lateral view 0.36 mm and in top view 0.50 mm. Differences between the diameters of the electrode 9 and 2 were highly significant. Interestingly, the real diameter of the electrode is half in comparison to the radiological one. Also in comparison to the diameter of the cable and the associated electrode is nearly half. Nearly 50% artifact exists on radiologic evaluation of the diameter of the electrode. Varying the X-ray adjustments did not lead to optimized results. The difficulties in evaluating a cochlea electrode with CBT could be shown. The high rate of artifacts (50%) makes it extremely difficult to predict the inserted scale, especially when evaluating the intracochlear position in the medial and apical turn of the cochlea. In conclusion, until now CBT allows a relatively safe evaluation of the electrode in the basal turn, whereas in deep insertion it is not really a useful tool to answer the question of insertion trauma, implanted scale, or scale displacements.

Cone Beam and Micro-Computed Tomography Validation of Manual Array Insertion for Minimally Invasive Cochlear Implantation

“…Furthermore, CBCT has reduced radiation exposure compared with conventional multislice CT imaging [Cushing et al, 2012;Kurzweg et al, 2010]. The imaging resolution is, however, insufficient for the assessment of intracochlear trauma, and the radiologically measured electrode array diameter is exaggerated due to imaging artifacts [Güldner et al, 2012]. We observed that the CBCT scans provided a sufficient image resolution and quality for estimation of the implanted scala in all cases imaged ( table 1 ).…”

Prospective evaluation of reliability of cone‐beam computed tomography in detecting different position of vibroplasty middle ear implants

“…The use of cone‐beam CT for the imaging of the head and neck, especially at the anterior and lateral skull base, has been described before . Cone‐beam CT is also a useful tool for the imaging of cochlear implants for quality control and for detecting the intracochlear position of the electrode . Controversy still exists regarding the dosage of cone‐beam CT in comparison with conventional CT for the imaging of the anterior and lateral skull base.…”

“…Therefore, an intraoperative cone‐beam computed tomography (CT) or conventional CT is currently considered the best solution. Intraoperative imaging in ENT surgery is presently dependent on cone‐beam CT, because of lower radiation exposure and lower artefacts . The use of imaging along with VSB has been limited.…”

Micro-CT scan, electron microscopy and optical microscopy study of insertional traumas of cochlear implants

“…The images do not enable evaluation of the atraumatic nature of the implantation or the preservation of residual hearing. The recent development of the Cone Beam provides new information, and the advantages of this technique in evaluating cochlear trauma are currently being verified in histological samples and in patients [4,8,9].…”