Radiation dose reduction in postoperative computed position control of cochlear implant electrodes in lambs – An experimental study

• Postoperative CI electrode position control was achieved with reduced radiation dose.
• Tube current–time product and tube voltage can be reduced by 50%.
• Our lamb model supports future low-dose CT protocols in children.

ObjectiveCochlear implants (CI) are standard treatment for prelingually deafened children and postlingually deafened adults. Computed tomography (CT) is the standard method for postoperative imaging of the electrode position. CT scans accurately reflect electrode depth and position, which is essential prior to use. However, routine CT examinations expose patients to radiation, which is especially problematic in children. We examined whether new CT protocols could reduce radiation doses while preserving diagnostic accuracy.MethodsTo investigate whether electrode position can be assessed by low-dose CT protocols, a cadaveric lamb model was used because the inner ear morphology is similar to humans. The scans were performed at various volumetric CT dose-indexes CTDIvol)/kV combinations. For each constant CTDIvol the tube voltage was varied (i.e., 80, 100, 120 and 140 kV). This procedure was repeated at different CTDIvol values (21 mGy, 11 mGy, 5.5 mGy, 2.8 mGy and 1.8 mGy). To keep the CTDIvol constant at different tube voltages, the tube current values were adjusted. Independent evaluations of the images were performed by two experienced and blinded neuroradiologists. The criteria diagnostic usefulness, image quality and artifacts (scaled 1–4) were assessed in 14 cochlear-implanted cadaveric lamb heads with variable tube voltages.ResultsResults showed that the standard CT dose could be substantially reduced without sacrificing diagnostic accuracy of electrode position. The assessment of the CI electrode position was feasible in almost all cases up to a CTDIvol of 2–3 mGy. The number of artifacts did not increase for images within this dose range as compared to higher dosages. The extent of the artifacts caused by the implanted metal-containing CI electrode does not depend on the radiation dose and is not perceptibly influenced by changes in the tube voltage.Summarizing the evaluation of the CI electrode position is possible even at a very low radiation dose.ConclusionsCT imaging of the temporal bone for postoperative electrode position control of the CI is possible with a very low and significantly radiation dose. The tube current–time product and voltage can be reduced by 50% without increasing artifacts. Low-dose postoperative CT scans are sufficient for localizing the CI electrode.