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Validation of a Cochlear Implant Patient-Specific Model of the Voltage Distribution in a Clinical Setting

View Article: PubMed Central - PubMed

ABSTRACT

Cochlear Implants (CIs) are medical implantable devices that can restore the sense of hearing in people with profound hearing loss. Clinical trials assessing speech intelligibility in CI users have found large intersubject variability. One possibility to explain the variability is the individual differences in the interface created between electrodes of the CI and the auditory nerve. In order to understand the variability, models of the voltage distribution of the electrically stimulated cochlea may be useful. With this purpose in mind, we developed a parametric model that can be adapted to each CI user based on landmarks from individual cone beam computed tomography (CBCT) scans of the cochlea before and after implantation. The conductivity values of each cochlea compartment as well as the weighting factors of different grounding modes have also been parameterized. Simulations were performed modeling the cochlea and electrode positions of 12 CI users. Three models were compared with different levels of detail: a homogeneous model (HM), a non-patient-specific model (NPSM), and a patient-specific model (PSM). The model simulations were compared with voltage distribution measurements obtained from the backward telemetry of the 12 CI users. Results show that the PSM produces the lowest error when predicting individual voltage distributions. Given a patient-specific geometry and electrode positions, we show an example on how to optimize the parameters of the model and how to couple it to an auditory nerve model. The model here presented may help to understand speech performance variability and support the development of new sound coding strategies for CIs.

No MeSH data available.


Voltage distribution, activation function, and excitation profiles when electrode 10 is stimulated using the P1, P7, and the NPSM2 models with a conductivity ratio R = 71.5. The left panel shows the voltage distributions in volts [V] along each nerve fiber and along the basilar membrane. The central panel presents the corresponding activation function in [V/mm2]. The right panel indicates which neurons are excited when stimulating electrode 10 (excitation profile). The black areas in the excitation profile indicate stimulation in the axon, the gray areas represent stimulation in the most peripheral process, and the white area means no excitation.
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Figure 12: Voltage distribution, activation function, and excitation profiles when electrode 10 is stimulated using the P1, P7, and the NPSM2 models with a conductivity ratio R = 71.5. The left panel shows the voltage distributions in volts [V] along each nerve fiber and along the basilar membrane. The central panel presents the corresponding activation function in [V/mm2]. The right panel indicates which neurons are excited when stimulating electrode 10 (excitation profile). The black areas in the excitation profile indicate stimulation in the axon, the gray areas represent stimulation in the most peripheral process, and the white area means no excitation.

Mentions: Using the activation function provided in Eq. 4 and the auditory model presented in Section “Auditory Nerve Model,” we give insight on the effects of different conductivity values as well as geometries in the activation function and auditory nerve excitation profiles. Figures 11 and 12 present the voltage distribution, the magnitude of the activation function, and the excitation profile for the NPSM2, and two versions of the PSM models (P1 and P7) when electrode 10 is stimulated. Excitation profiles (Kalkman et al., 2014) indicate which neurons are excited when stimulating a given electrode. The activation function given in Eq. 4 was estimated in 10 μm length segments. The black areas in the excitation profile indicate stimulation in the soma (node 5), the gray areas represent stimulation in the peripheral process (node 1), and the white area means no excitation.


Validation of a Cochlear Implant Patient-Specific Model of the Voltage Distribution in a Clinical Setting
Voltage distribution, activation function, and excitation profiles when electrode 10 is stimulated using the P1, P7, and the NPSM2 models with a conductivity ratio R = 71.5. The left panel shows the voltage distributions in volts [V] along each nerve fiber and along the basilar membrane. The central panel presents the corresponding activation function in [V/mm2]. The right panel indicates which neurons are excited when stimulating electrode 10 (excitation profile). The black areas in the excitation profile indicate stimulation in the axon, the gray areas represent stimulation in the most peripheral process, and the white area means no excitation.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5120131&req=5

Figure 12: Voltage distribution, activation function, and excitation profiles when electrode 10 is stimulated using the P1, P7, and the NPSM2 models with a conductivity ratio R = 71.5. The left panel shows the voltage distributions in volts [V] along each nerve fiber and along the basilar membrane. The central panel presents the corresponding activation function in [V/mm2]. The right panel indicates which neurons are excited when stimulating electrode 10 (excitation profile). The black areas in the excitation profile indicate stimulation in the axon, the gray areas represent stimulation in the most peripheral process, and the white area means no excitation.
Mentions: Using the activation function provided in Eq. 4 and the auditory model presented in Section “Auditory Nerve Model,” we give insight on the effects of different conductivity values as well as geometries in the activation function and auditory nerve excitation profiles. Figures 11 and 12 present the voltage distribution, the magnitude of the activation function, and the excitation profile for the NPSM2, and two versions of the PSM models (P1 and P7) when electrode 10 is stimulated. Excitation profiles (Kalkman et al., 2014) indicate which neurons are excited when stimulating a given electrode. The activation function given in Eq. 4 was estimated in 10 μm length segments. The black areas in the excitation profile indicate stimulation in the soma (node 5), the gray areas represent stimulation in the peripheral process (node 1), and the white area means no excitation.

View Article: PubMed Central - PubMed

ABSTRACT

Cochlear Implants (CIs) are medical implantable devices that can restore the sense of hearing in people with profound hearing loss. Clinical trials assessing speech intelligibility in CI users have found large intersubject variability. One possibility to explain the variability is the individual differences in the interface created between electrodes of the CI and the auditory nerve. In order to understand the variability, models of the voltage distribution of the electrically stimulated cochlea may be useful. With this purpose in mind, we developed a parametric model that can be adapted to each CI user based on landmarks from individual cone beam computed tomography (CBCT) scans of the cochlea before and after implantation. The conductivity values of each cochlea compartment as well as the weighting factors of different grounding modes have also been parameterized. Simulations were performed modeling the cochlea and electrode positions of 12 CI users. Three models were compared with different levels of detail: a homogeneous model (HM), a non-patient-specific model (NPSM), and a patient-specific model (PSM). The model simulations were compared with voltage distribution measurements obtained from the backward telemetry of the 12 CI users. Results show that the PSM produces the lowest error when predicting individual voltage distributions. Given a patient-specific geometry and electrode positions, we show an example on how to optimize the parameters of the model and how to couple it to an auditory nerve model. The model here presented may help to understand speech performance variability and support the development of new sound coding strategies for CIs.

No MeSH data available.