Intraoperative transimpedance and spread of excitation profile correlations with a lateral-wall cochlear implant electrode array

Söderqvist, Samuel; Lamminmäki, Satu; Aarnisalo, Antti A.; Hirvonen, Timo; Sinkkonen, Saku T.; Sivonen, Ville

doi:10.1016/j.heares.2021.108235

Cited by 20 publications

(24 citation statements)

References 30 publications

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“…For example, any research study that utilizes intra-operative ECAP measures (e.g. Söderqvist et al, 2021) could benefit from collecting all Spread of Excitation functions of interest instead of being restricted in their data collection by limited time in the operating theatre. Of course this is not limited to the operating theatre; even in research settings where multiple hours are available for data collection from cochlear implant research volunteers, collecting ECAP data in a more efficient way allows for more conditions to be evaluated without extending research time.…”

Section: Discussionmentioning

confidence: 99%

SpeedCAP: An Efficient Method for Estimating Neural Activation Patterns Using Electrically-Evoked Compound Action-Potentials in Cochlear Implant Users

Garcia¹,

Deeks²,

Goehring³

et al. 2021

Preprint

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Objectives: Electrically-Evoked Compound Action-Potentials (ECAPs) can be recorded using the electrodes in a cochlear implant (CI) and represent the synchronous responses of the electrically-stimulated auditory-nerve. ECAPs can be obtained using a forward-masking method that measures the neural response to a probe and masker electrode separately and in combination. The Panoramic ECAP (PECAP) method measures ECAPs using multiple combinations of masker and probe electrodes and uses a nonlinear optimization algorithm to estimate current spread from each electrode and neural health along the cochlea. However, the measurement of ECAPs from multiple combinations of electrodes is too time-consuming for use in clinics. This study proposes and evaluates a fast version of the PECAP measurements, SpeedCAP, that minimises recording time by exploiting redundancies between multiple ECAP measures, and that can be applied to methods where multiple ECAPs are required. Design: In the first study, 11 users of Cochlear Limited CIs took part. ECAPs were recorded using the forward-masking artefact-cancellation technique at the most comfortable loudness level (MCL) for every combination of masker and probe electrodes for all active electrodes in the users’ MAPs, as per the standard PECAP recording paradigm. The same current levels and recording parameters were then used to collect ECAPs in the same users with the SpeedCAP method. The ECAP amplitudes were then compared between the two conditions, as were the corresponding estimates of neural health and current spread calculated using the PECAP method described by Garcia et al (2021). The second study measured SpeedCAP intra-operatively in 8 CI patients and with all maskers and probes presented at the same current level to assess feasibility. ECAPs for the subset of conditions where the masker and probe were presented on the same electrode were compared to those obtained using the slower approach leveraged by the standard clinical software. Results: Data collection time was reduced from 45 (PECAP) to 8 (SpeedCAP) minutes. There were no significant differences between normalized root mean squared error (RMSE) repeatability metrics for post-operative PECAP and SpeedCAP data, nor for the RMSEs calculated between PECAP and SpeedCAP data. When between-participant differences were removed, both the neural health (r = 0.73) and current spread (r = 0.65) estimates were significantly correlated (p < 0.0001, df = 218) between SpeedCAP and PECAP conditions across all electrodes. Valid ECAPs were obtained in all patients in the second study, demonstrating intra-operative feasibility of SpeedCAP. No significant differences in RMSEs were detectable between post- and intra-operative ECAP measurements. Conclusions: The improved efficiency of SpeedCAP provides time savings facilitating multi-electrode ECAP recordings in routine clinical practice. The SpeedCAP data collection is sufficiently quick to record intra-operatively, and adds no significant error to the ECAP amplitudes. Such measurements could thereafter be submitted to models such as PECAP to provide patient-specific patterns of neural activation to inform programming of clinical MAPs and/or identify causes of poor performance at the electrode-nerve interface of CI users. The speed and accuracy of these measurements also opens up a wide range of additional research questions to be addressed.

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Section: Discussionmentioning

confidence: 99%

SpeedCAP: An Efficient Method for Estimating Neural Activation Patterns Using Electrically-Evoked Compound Action-Potentials in Cochlear Implant Users

Garcia¹,

Deeks²,

Goehring³

et al. 2021

Preprint

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“…CI users suffer from insufficient spectral resolution due to channel interaction. Theoretically, an electrode stimulates the area directly facing it, but the electrical field generated by one stimulating electrode can cause the stimulation of neighboring spiral ganglion neurons [ 67 , 68 ]. Figure 3 shows this phenomenon, which is known as the spread of neural excitation (SOE).…”

Section: Electrode and Electrode Array Designmentioning

confidence: 99%

“…Figure 3 shows this phenomenon, which is known as the spread of neural excitation (SOE). Unwanted overlaps of excitation may change the efficiency of subsequent stimuli, or, if sufficient, it can trigger the firing of neighboring neurons, which leads to poor vowel and consonant recognition and poor auditory rehabilitation [ 67 ]. Even though current CIs have 12–22 electrodes and channels, due to channel interactions, the number of independent channels is smaller than the actual number of activated electrodes [ 66 ].…”

Section: Electrode and Electrode Array Designmentioning

confidence: 99%

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Recent Advances in Cochlear Implant Electrode Array Design Parameters

et al. 2022

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Cochlear implants are neural implant devices that aim to restore hearing in patients with severe sensorineural hearing impairment. Here, the main goal is to successfully place the electrode array in the cochlea to stimulate the auditory nerves through bypassing damaged hair cells. Several electrode and electrode array parameters affect the success of this technique, but, undoubtedly, the most important one is related to electrodes, which are used for nerve stimulation. In this paper, we provide a comprehensive resource on the electrodes currently being used in cochlear implant devices. Electrode materials, shape, and the effect of spacing between electrodes on the stimulation, stiffness, and flexibility of electrode-carrying arrays are discussed. The use of sensors and the electrical, mechanical, and electrochemical properties of electrode arrays are examined. A large library of preferred electrodes is reviewed, and recent progress in electrode design parameters is analyzed. Finally, the limitations and challenges of the current technology are discussed along with a proposal of future directions in the field.

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“…(2010) found that loudness was determined by the Z eff , and both loudness and the Z eff increased with the stimulating current. In our earlier study ( Söderqvist et al., 2021 ), we substituted the recorded transimpedance at the location of the stimulating electrode with a Z eff to estimate an effective intracochlear EF (EF eff ), which allowed a more realistic comparison between the widths of the EF eff and neural activation. We found that the profiles and widths of the EF eff correlate with the patterns of the activated SGNs, as measured with the forward-masking paradigm for the spread of neural excitation.…”

Section: Introductionmentioning

confidence: 99%

The intraoperative relationship between intracochlear electrical field and excitability of the auditory nerve

Söderqvist¹,

Sinkkonen²,

Sivonen³

2022

Heliyon

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Intraoperative transimpedance and spread of excitation profile correlations with a lateral-wall cochlear implant electrode array

Cited by 20 publications

References 30 publications

SpeedCAP: An Efficient Method for Estimating Neural Activation Patterns Using Electrically-Evoked Compound Action-Potentials in Cochlear Implant Users

SpeedCAP: An Efficient Method for Estimating Neural Activation Patterns Using Electrically-Evoked Compound Action-Potentials in Cochlear Implant Users

Recent Advances in Cochlear Implant Electrode Array Design Parameters

The intraoperative relationship between intracochlear electrical field and excitability of the auditory nerve

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