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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.


(A) Cochlear dimensions estimated from CBCT. A and B values in CBCT data as clinically derived measures. (B) Height (H) of the cochlea starting from the lowest basal point to the apex (Helicotrema).
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Figure 1: (A) Cochlear dimensions estimated from CBCT. A and B values in CBCT data as clinically derived measures. (B) Height (H) of the cochlea starting from the lowest basal point to the apex (Helicotrema).

Mentions: Temporal bone CBCT data were collected using a stationary Xoran MiniCat (Ann Arbor, MI, USA) equipped with a 536 × 536 matrix detector resulting in 0.3 mm × 0.3 mm × 0.3 mm isotropic voxels (125 kVp, 7 mA). DICOM data processing was performed with OsiriX MD (Pixmeo, Geneva, Switzerland) using a 3D curved multiplanar reconstruction (MPR) tool. The starting point at the lateral wall of the cochlea was characterized by identifying the distal bony rim of the round window (A1 in Figure 1A). Next, a curve was set up in three-dimensions along the outer edge of the bony cochlea in projection of the osseous spiral lamina following the same method as Würfel et al. (2014). The endpoint was defined by the helicotrema (H2).


Validation of a Cochlear Implant Patient-Specific Model of the Voltage Distribution in a Clinical Setting
(A) Cochlear dimensions estimated from CBCT. A and B values in CBCT data as clinically derived measures. (B) Height (H) of the cochlea starting from the lowest basal point to the apex (Helicotrema).
© Copyright Policy
Related In: Results  -  Collection

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

Figure 1: (A) Cochlear dimensions estimated from CBCT. A and B values in CBCT data as clinically derived measures. (B) Height (H) of the cochlea starting from the lowest basal point to the apex (Helicotrema).
Mentions: Temporal bone CBCT data were collected using a stationary Xoran MiniCat (Ann Arbor, MI, USA) equipped with a 536 × 536 matrix detector resulting in 0.3 mm × 0.3 mm × 0.3 mm isotropic voxels (125 kVp, 7 mA). DICOM data processing was performed with OsiriX MD (Pixmeo, Geneva, Switzerland) using a 3D curved multiplanar reconstruction (MPR) tool. The starting point at the lateral wall of the cochlea was characterized by identifying the distal bony rim of the round window (A1 in Figure 1A). Next, a curve was set up in three-dimensions along the outer edge of the bony cochlea in projection of the osseous spiral lamina following the same method as Würfel et al. (2014). The endpoint was defined by the helicotrema (H2).

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.