Andreas Pomschar MD, Presenter: Equipment support, MED-EL GmbH

Melvin D'Anastasi, Abstract Co-Author: Nothing to Disclose

Ullrich Kisser, Abstract Co-Author: Nothing to Disclose

Denise Steffinger RT, Abstract Co-Author: Nothing to Disclose

Maximilian F. Reiser MD, Abstract Co-Author: Nothing to Disclose

John Martin Hempel, Abstract Co-Author: Nothing to Disclose

Joachim Mueller, Abstract Co-Author: Nothing to Disclose

Birgit Betina Ertl-Wagner MD, Abstract Co-Author: Scientific Advisory Board, Koninklijke Philips Electronics NV Consultant, Bracco Group Travel support, Siemens AG

To investigate the feasibility and accuracy of length measurements of the cochlear implant (CI) electrode by high-resolution computed tomography (HR-CT) using CI electrodes of a predefined length in human temporal bone specimens.

Eight human temporal bone specimens were surgically prepared analogous to a regular CI surgery for the study. The round window was opened and the cochleae were then injected with a physiologic saline solution to avoid air bubbles, which could interfere with CT scanning. Dummy-electrodes by MED-EL with two markers in a predefined distance of 20 mm were inserted and fixated in the round window. Two temporal bones at a time were inserted into both sides of a plastic head phantom and HR-CT imaging was performed with a dual source CT (Somatom FLASH, Siemens). The data were reconstructed with a slice thickness of 0.4 mm, an increment of 0.1 mm in a maximum-intensity-projection technique (MIP). For data analysis OsiriX (version 4.1, 64-bit) was applied using a 3D-curved MPR technique. Readings were performed by 4 M.D.s of differing experience (Reader 1: otolaryngology resident, Reader 2: junior radiology resident, Reader 3: senior radiology resident, Reader 4: head and neck staff radiologist). Mean values and standard deviation for time and measured length were calculated.For statistical analysis we performed a linear mixed effects model for modeling the deviations from the true value (20 mm) where the raters are treated as random effects. Intraclass correlation 0.133)

The mean measurement error from 20 mm over all specimens and readers was 0.9 mm ±0. 9 (reader 1 to 4: 1.2mm ±1.2 ; 0.8mm ±0.8; 1.0mm ±0.8; 0.7 mm ± 2.3, respectively). The time needed to measure one electrode was similar for all readers with an average of 6.06 min ±3.40min. Electrode markers were reliably identified by all readers in all specimen. The average bias was 0.032cm and statistically not significant (p = 0.71))

Our results show that CT based measurement of cochlear implant length is highly accurate and can be done in a limited time. This may aid in the post-operative assessment of electrode positioning.

As CI electrode length measurements by HRCT were highly accurate in this experimental setting, post-operative assessments of inserted electrode length with curved MPR-techniques appear feasible.

Pomschar, A, D'Anastasi, M, Kisser, U, Steffinger, D, Reiser, M, Hempel, J, Mueller, J, Ertl-Wagner, B, Accuracy of CT-based Length Assessments of Cochlear Implant (CI) Electrodes in Human Temporal Bone Specimens.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12038187.html