Limits...
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.


(A) Effect of different ratios R = σST/σB on the intra-cochlear voltage recordings when electrode 11 is stimulated using the NPSM model. With decreasing values of R, the voltage distribution becomes wider. The mean of the voltage distribution has been subtracted. (B) Effect of different electrode positions on the intra-cochlea voltage distribution. The central positions correspond with the electrode positions estimated from the imaging data, and the modiolar and lateral positions correspond with a displacement of 0.5 mm toward the modiolar or lateral direction. The voltage distribution model predicts wider intra-cochlear voltage distribution when the electrodes are shifted toward the modiolus.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC5120131&req=5

Figure 7: (A) Effect of different ratios R = σST/σB on the intra-cochlear voltage recordings when electrode 11 is stimulated using the NPSM model. With decreasing values of R, the voltage distribution becomes wider. The mean of the voltage distribution has been subtracted. (B) Effect of different electrode positions on the intra-cochlea voltage distribution. The central positions correspond with the electrode positions estimated from the imaging data, and the modiolar and lateral positions correspond with a displacement of 0.5 mm toward the modiolar or lateral direction. The voltage distribution model predicts wider intra-cochlear voltage distribution when the electrodes are shifted toward the modiolus.

Mentions: The NPSM and PSM models were designed using fixed parameter values. Given a personalized cochlea geometry and electrode positions, it is possible to optimize the model modifying the parameters such that the difference between the modeled and measured intra-cochlear voltage values is minimized. It has been shown that the ratio between the conductivity values of the scala tympani and the bone R = σST/σB plays a major role in defining the current paths in the cochlea. For example, keeping the σST constant and lowering the σB to 0.0017 Sm−1 has an effect on both the magnitude and shape of the current distribution across cochlear position as shown by Frijns et al. (1995) and Hanekom (2001). This effect is shown in Figure 7A where simulations of the intra-cochlear voltage distribution are presented using the NPSM model for different ratios R when electrode 11 is stimulated. The value of σST was kept constant, and the value of σB was varied resulting in the different ratios R.


Validation of a Cochlear Implant Patient-Specific Model of the Voltage Distribution in a Clinical Setting
(A) Effect of different ratios R = σST/σB on the intra-cochlear voltage recordings when electrode 11 is stimulated using the NPSM model. With decreasing values of R, the voltage distribution becomes wider. The mean of the voltage distribution has been subtracted. (B) Effect of different electrode positions on the intra-cochlea voltage distribution. The central positions correspond with the electrode positions estimated from the imaging data, and the modiolar and lateral positions correspond with a displacement of 0.5 mm toward the modiolar or lateral direction. The voltage distribution model predicts wider intra-cochlear voltage distribution when the electrodes are shifted toward the modiolus.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 7: (A) Effect of different ratios R = σST/σB on the intra-cochlear voltage recordings when electrode 11 is stimulated using the NPSM model. With decreasing values of R, the voltage distribution becomes wider. The mean of the voltage distribution has been subtracted. (B) Effect of different electrode positions on the intra-cochlea voltage distribution. The central positions correspond with the electrode positions estimated from the imaging data, and the modiolar and lateral positions correspond with a displacement of 0.5 mm toward the modiolar or lateral direction. The voltage distribution model predicts wider intra-cochlear voltage distribution when the electrodes are shifted toward the modiolus.
Mentions: The NPSM and PSM models were designed using fixed parameter values. Given a personalized cochlea geometry and electrode positions, it is possible to optimize the model modifying the parameters such that the difference between the modeled and measured intra-cochlear voltage values is minimized. It has been shown that the ratio between the conductivity values of the scala tympani and the bone R = σST/σB plays a major role in defining the current paths in the cochlea. For example, keeping the σST constant and lowering the σB to 0.0017 Sm−1 has an effect on both the magnitude and shape of the current distribution across cochlear position as shown by Frijns et al. (1995) and Hanekom (2001). This effect is shown in Figure 7A where simulations of the intra-cochlear voltage distribution are presented using the NPSM model for different ratios R when electrode 11 is stimulated. The value of σST was kept constant, and the value of σB was varied resulting in the different ratios R.

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.