Unwrapping cochlear implants by spiral CT

• Published in: IEEE transactions on biomedical engineering Vol. 43; no. 9; pp. 891 - 900
• Main Authors: Ge Wang, Vannier, M.W., Skinner, M.W., Kalender, W.A., Polacin, A., Ketten, D.R.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.09.1996; Institute of Electrical and Electronics Engineers
• Subjects: Algorithms; Auditory implants; Biological and medical sciences; Cochlea - diagnostic imaging; Cochlear Implants; Computed tomography; Deafness; Ear; Electrodes; Electrodes, Implanted; Feasibility Studies; Head and neck surgery. Maxillofacial surgery. Dental surgery. Orthodontics; Hearing aids; Humans; Image Processing, Computer-Assisted; In vitro; Length measurement; Medical sciences; Prosthesis Design; Spirals; Surface Properties; Surgery (general aspects). Transplantations, organ and tissue grafts. Graft diseases; Surgery of the ear, the auditive nerve and the facial nerve; Tomography, X-Ray Computed; Test objet; Volumetric analysis; Radiodiagnosis; Prosthesis; Auditory disorder; Image reconstruction; Hearing loss; Biomedical data processing; Surgical implantation; Algorithm performance; Spiral structure; Speech recognition; Cochlea; Position measurement; ENT disease; Computerized axial tomography; Multielectrode device
• ISSN: 0018-9294; 1558-2531
• DOI: 10.1109/10.532123

Multielectrode, intracochlear implants were designed for individuals with profound sensorineural hearing loss who derive little or no benefit from acoustic hearing aids. Determination of each electrode's position in a patient's inner ear may improve speech processor programming to maximize speech recognition. In this paper, an approach is described to use as input a volumetric spiral computed tomography (CT) image of the Nucleus electrode array (Cochlear Pty. Ltd, Lane Cove, NSW, Australia) to unwrap it, and to measure its implanted length given starting and end points. Representative curvilinear structures were digitally synthesized in image volumes of isotropic 0.1-mm voxels. The electrode array was spirally CT-scanned in vitro and in vivo, and reconstructed on an isotropic grid in 0.1-mm steps. Two algorithms were constructed to track and measure these curvilinear structures. The first algorithm is Karhunen-Loeve (K-L)-transform based, in which the K-L transform is locally applied at a current main aids position to determine the eigenvectors of the main axis voxels, the next main axis position is estimated from the current position along the principal eigendirection, adjusted to the mass center of the orthogonal cross section passing through the estimated position, and then scaled to have a prespecified step. The second algorithm is similar to the first one but avoids use of the K-L transform, in the second algorithm, the next position is directly estimated along the local direction and then processed with the same correction and scaling operations. With user-specified starting and end points as well. As a local direction at the starting point, a curvilinear structure can be automatically tracked using either of the algorithms. The first algorithm is more robust, while the second one is more efficient. In the numerical and in vitro studies, the lengths of the curvilinear structures were accurately measured. Given local directions determined in the tracking process, an electrode array image can be unwrapped into a linear array with the central electrode axis as the abscissa. The unwrapping approach allows longitudinally and cross-sectionally accurate measurement and better visualization of cochlear implant images. With preimplantation knowledge of length, width, and center electrode distance, the position of individual electrodes can be estimated after unwrapping.