Cochlear duct length along the outer wall vs organ of corti: Which one is relevant for the electrode array length selection and frequency mapping using Greenwood function?

Cochlear duct length (CDL) measurement or estimation is a hot topic for various research groups in the cochlear implant (CI) field as of today.Getting the CDL along the outer wall (LW) and organ of corti (OC) is possible but considering the clinical application especially in the selection of the electrode array length and applying Greenwood's frequency function,we need to have a clear understanding on the CDL in general and as well on the Greenwood's frequency function.It is very clear from the histology images of the cochlea with straight electrode inside,that the electrode locates itself right under the basilar membrane.Also the Greenwood's frequency function involves a variable that corresponds to the CDL at the basilar membrane/organ of corti level This brings us to conclude that the CDL at the OC is relevant for the selection of electrode array length and in applying Greenwood's frequency function.The ratio between CDL (LW) and CDL (OC) is 0.9 which is a very important number that needs to be remembered when converting CDL (LW) to CDL (OC).

The rationale for FLEX (cochlear implant) electrode with varying array lengths

With cochlear implantation(CI)being the standard of care for profoundly deaf cases,more and more patients with low frequency residual hearing are currently being treated with CI.In view of preserving the residual hearing,the ultimate aim of both the surgeons and the CI companies is to achieve zero-degree of electrode insertion trauma.Variations in the size and shape of cochlea,cross-sectional dimensions of ST,electrode insertion techniques with and without metal stylet rod and the experience level of the operating surgeons,all play a role in the electrode array related insertion trauma.An effective electrode design must include flexible array to accommodate the cochlear shape variation,electrode with variety of array lengths to support the concept of cochlear size specific electrode array and finally smaller cross-sectional dimensions of electrode array in matching the cross-sectional dimensions of ST.As per published reports,FLEX electrode array design offers minimal degree of electrode insertion trauma along with the possibility of patient specific electrode array length matching their cochlear size.Looking at the cross-sectional dimensions of FLEX electrode array along with its volume,it appear to be highly safe to the cochlea by not taking too much volume inside the ST.To offer additional support,otological pre-planning software tool like OTOPLAN is now clinically available in measuring the cochlear size in finding the best electrode array match along with the possibilities of anatomy based post-operative speech processor fitting.

Research software in cochlear duct length estimation,Greenwood frequency mapping and CI electrode array length simulation

Background and objective:The size of the cochlea varies a lot among the human population bringing the necessity for electrode arrays to be available in various lengths irrespective of the cochlear implant(CI)brand.This research software helps in the estimation of the patient’s cochlear duct length(CDL)which is then used for the simulation of the correct length electrode array matching the patient’s cochlear size and as well in getting the patient specific cochlear frequency map.Methods:Visual Studio Express 2012 for Windows Desktop is used in the architecture of this research software.The basal turn diameter of the cochlea("A"value)needs to be measured from the pre-operative computed tomography(CT)image of the patient’s temporal bone.This"A"will be taken as the input for the CDL equations proposed by Alexiades et al for estimating the CDL along the basilar membrane for various insertion depths.Greenwood’s equation is then used in combination with the CDL for the full length of the cochlea in getting the patient specific frequency map.Results:The research software with the help of the"A"value as input,with few button clicks,gives the patient specific CDL for various insertion depths and the Greenwood’s frequency map.The users have the choice to select any electrode array of their choice and place it under the frequency map to see how good it fits to that particular patient’s cochlea.Also,given the possibility to drag and move the electrode array picture to mimic the post-operative actual electrode insertion depth.Conclusions:This research software simplifies the overall process of CDL estimation and in getting the patient specific cochlear frequency map.The clinicians get the chance to simulate placing the various electrode array lengths in patient cochlea in identifying the best fit electrode.This could help in pushing the CI field into the concept of individualized CI electrode array solution that ultimately benefits the patients.