Semi-automated evaluation of high resolution MRI for preoperative cochlear implant screening

The success of cochlear implants requires a functioning auditory nerve. An accurate non-invasive method of screening cochlear implant candidates for quantitative measurement of auditory nerve viability would allow physicians to better determine the efficacy of the procedure. To investigate the relationship between auditory nerve size and its functionality, we made morphological measurements of the auditory and facial nerves and correlated these measurements with audiologic test results. The study included 11 cochlear implant candidates. Non-invasive high-resolution bilateral MR images were acquired from 3T and 1.5T scanners. A semi-automated segmentation technique was developed which allows effective segmentation of multiple slices of MRI data. Segmentation involved morphological processing of the original filtered image to isolate the auditory and facial nerves. The volumes of both nerves were computed from segmented continuous saggital slices, and their ratios were computed. This technique is promising and should allow accurate, reproducible and rapid segmentation of the auditory and facial nerves for accurate volume measurements. Correlation of the anatomic measurements of the subjects with the functional findings of collaborating audiologists was carried out. Preliminary results suggest that there is a minimum threshold of ratios, which is indicative of a degenerated nerve, and consequently a higher risk for unsuccessful cochlear implant.