On the accuracy of cochlear duct length measurement in computed tomographic images
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Patient specific selection of cochlear implants would benefit from pre-operative knowledge of cochlear length. Several methods for its measurement or estimation have been described in literature. This study focused on the achievable accuracy in clinically available imaging.
Five simplified cochlea models milled into porcine bone were scanned in water using clinical cone beam computed tomography. Due to their well-known dimensions these phantoms served as gold standard for the length measurements. Each phantom was measured ten times using the custom software Comet. In addition, cochleae in ten image datasets taken indiscriminately from clinical routine were measured ten times each to test the precision under realistic conditions. The results were also compared to estimations based on the diameter of the basal turn (A value) as described in literature.
Measurement accuracy of the phantoms’ lengths was high (average error: − 0.2 mm; standard deviation: 0.3 mm). The pooled standard deviation for the measurements in clinical datasets was 0.6 mm. Errors resulted mainly from problems locating the helicotrema. The estimations differed on average − 1.7 to + 0.4 mm from the manual measurements and had standard deviations between 0.5 and 0.6 mm depending on the algorithm.
The program Comet was successfully used to accurately measure the length of the cochlea models in clinically available imaging. The lower image quality of patient scans reduced the precision of the measurement. Estimations using the A value are a quicker alternative for averagely sized cochleae in cases where the lack of accuracy is tolerable.
KeywordsCochlear implant In-vitro verification Midmodiolar view
The presented work was supported by the German Research Foundation (DFG) through the cluster of excellence “Hearing4all” EXC 1077/1 and by the German Federal Ministry of Education and Research (BMBF, FKZ 13GW0019E). Responsibility for the contents of this publication lies with the authors.
Compliance with ethical standards
Conflict of interest
G. Jakob Lexow, Marcel Kluge, Nils-Claudius Gellrich, Thomas Lenarz, Omid Majdani and Thomas S. Rau declare that they have no conflict of interest.
This article does not contain any studies with human participants or animals performed by any of the authors.
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