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Co-Registration of Cone Beam CT and Pre-operative MRI for Electrode Localisation Following Cochlear Implantation
Dragovic A1, Stringer AK1, Campbell L2, O’Leary S2, Briggs R2
1 Department of Otolaryngology, The Royal Victorian Eye and Ear Hospital, East Melbourne
2 Department of Otolaryngology, University of Melbourne
Background:
Scala placement is one of the factors that predict outcome in cochlear implantation, furthermore, post-operative imaging for scalar localization of Cochlear Implant (CI) electrodes is shown to identify errors in technique that results in improved outcomes. This study aimed to determine whether co-registration of pre-operative MRIs with post-operative Cone Beam CTs (CBCT) was feasible in terms of time efficiency and beneficial to the surgeons and trainees that would be interpreting electrode localisation.
Method:
In a retrospective review of 20 randomly-selected patients, pre-operative MRI and post-operative CBCT images were co-registered using the image analysis software, AmiraTM. The time taken for each co-registration was recorded from two investigators. Using an internet survey program, ENT consultants and trainees were asked to decide in which scala they considered the electrode to be and then rank how easy or difficult they found each image set to interpret.
Results:
After an initial learning curve, the time to co-registration plateaued at a mean 10.83 min, with a significant improvement after the first 5 for each investigator (p<0.05). Both ENT consultants and trainees ranked the co-registered images as being easier to interpret (p < 0.05). Consultant otologists could predict scalar vestibuli location from CBCT alone with 100% sensitivity and 71% specificity.
Conclusion:
After a short learning curve, co-registration of MRI and CBCT can be performed time-efficiently. CBCT scans with suspicion of ST/SV translocation should be co-registered with the preoperative MRI to confirm placement.
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