Abstract
Cochlear implant surgery is a hearing restoration procedure for patients with profound hearing loss. In this surgery, an
electrode is inserted into the cochlea to stimulate the auditory nerve and restore the patient’s hearing. Clinical computed
tomography (CT) images are used for planning and evaluation of electrode placement, but their low resolution limits the
visualization of internal cochlear structures. Therefore, high resolution micro-CT images are used to develop atlas-based
segmentation methods to extract these nonvisible anatomical features in clinical CT images. Accurate registration of the
high and low resolution CT images is a prerequisite for reliable atlas-based segmentation. In this study, we evaluate and
compare different non-rigid B-spline registration parameters using micro-CT and clinical CT images of five cadaveric
human cochleae. The varying registration parameters are cost function (normalized correlation (NC), mutual information
and mean square error), interpolation method (linear, windowed-sinc and B-spline) and sampling percentage (1%, 10%
and 100%). We compare the registration results visually and quantitatively using the Dice similarity coefficient (DSC),
Hausdorff distance (HD) and absolute percentage error in cochlear volume. Using MI or MSE cost functions and linear or
windowed-sinc interpolation resulted in visually undesirable deformation of internal cochlear structures. Quantitatively,
the transforms using 100% sampling percentage yielded the highest DSC and smallest HD (0.828±0.021 and 0.25±0.09mm
respectively). Therefore, B-spline registration with cost function: NC, interpolation: B-spline and sampling percentage:
moments 100% can be the foundation of developing an optimized atlas-based segmentation algorithm of intracochlear
structures in clinical CT images.
