Atty. Docket No.3065.0754i Client Ref. No. CID03744WOPC1 IDENTIFYING FIBROSIS ALONG AN ELECTRODE ARRAY BACKGROUND Field of the Invention [0001] The present invention relates generally to identifying fibrosis along an electrode array of a hearing device. Related Art [0002] Medical devices have provided a wide range of therapeutic benefits to recipients over recent decades. Medical devices can include internal or implantable components/devices, external or wearable components/devices, or combinations thereof (e.g., a device having an external component communicating with an implantable component). Medical devices, such as traditional hearing aids, partially or fully-implantable hearing prostheses (e.g., bone conduction devices, mechanical stimulators, cochlear implants, etc.), pacemakers, defibrillators, functional electrical stimulation devices, and other medical devices, have been successful in performing lifesaving and/or lifestyle enhancement functions and/or recipient monitoring for a number of years. [0003] The types of medical devices and the ranges of functions performed thereby have increased over the years. For example, many medical devices, sometimes referred to as “implantable medical devices,” now often include one or more instruments, apparatus, sensors, processors, controllers or other functional mechanical or electrical components that are permanently or temporarily implanted in a recipient. These functional devices are typically used to diagnose, prevent, monitor, treat, or manage a disease/injury or symptom thereof, or to investigate, replace or modify the anatomy or a physiological process. Many of these functional devices utilize power and/or data received from external devices that are part of, or operate in conjunction with, implantable components. SUMMARY [0004] In one aspect, a method is provided. The method comprises: performing transimpedance matrix (TIM) measurements in response to stimulation of an electrode array implanted in a region of an inner ear of a recipient; analyzing the TIM measurements with a multi-layer model, wherein the multi-layer model includes a first layer representing a contact impedance, a second layer representing impedance associated with a fibrosis along the electrode array, and a third layer representing impedance associated with the inner ear region;
Atty. Docket No.3065.0754i Client Ref. No. CID03744WOPC1 and estimating an amount of the fibrosis along a length of the electrode array based on the multi-layer model. [0005] In another aspect, one or more non-transitory computer readable storage media are provided. The or more non-transitory computer readable storage comprise instructions that, when executed by one or more processors, are configured to: obtain measurements associated with an electrode array implanted in a recipient; construct a model based on the measurements, wherein the model indicating impedances associated with an electrode-tissue interface, impedances associated with a fibrosis along the electrode array, and impedances associated with body fluid of the recipient; and identify, from the model, an amount of the fibrosis at one or more electrodes of the electrode array. [0006] In another aspect, another method is provided. The method comprises: obtaining a plurality of transimpedance matrix (TIM) measurements associated with an electrode array implanted in a cochlea of a recipient over a period of time; and identifying an amount of fibrosis along a length of the electrode array based on the plurality of TIM measurements. [0007] In another aspect, another method is provided. The method comprises: obtaining, a plurality of measurements representing current spread from a plurality of electrodes in an inner ear of a recipient; and analyzing the plurality of measurements with a multi-layer model to estimate fibrosis at one or more of the plurality of electrodes. [0008] In another aspect, a device is provided. The device comprises: a memory; and at least one processor operable coupled to the memory, wherein the at least one processor is configured to: obtain a plurality of measurements representing current spread from a plurality of electrodes in an inner ear of a recipient; and analyze the plurality of measurements with a multi-layer model to estimate fibrosis at one or more of the plurality of electrodes. BRIEF DESCRIPTION OF THE DRAWINGS [0009] Embodiments of the present invention are described herein in conjunction with the accompanying drawings, in which: [0010] FIG. 1A is a schematic diagram illustrating a cochlear implant system with which aspects of the techniques presented herein can be implemented; [0011] FIG. 1B is a side view of a recipient wearing a sound processing unit of the cochlear implant system of FIG.1A;
Atty. Docket No.3065.0754i Client Ref. No. CID03744WOPC1 [0012] FIG.1C is a schematic view of components of the cochlear implant system of FIG.1A; [0013] FIG.1D is a block diagram of the cochlear implant system of FIG.1A; [0014] FIG.1E is a schematic diagram illustrating a computing device with which aspects of the techniques presented herein can be implemented; [0015] FIG.2A illustrates a post-operative transimpedance matrix (TIM) measurement; [0016] FIG. 2B illustrates a first model TIM generated based on the transimpedance matrix measurements of FIG.2A; [0017] FIG.2C illustrates a second model TIM generated based on the transimpedance matrix measurements of FIG.2A; [0018] FIG. 3 illustrates an exemplary diagram of a post-operative situation, according to certain embodiments described herein. [0019] FIGs. 4A, 4B, 4C, 4D, 4E, and 4F illustrate exemplary impedance measurements associated with a recipient over time, according to certain embodiments described herein. [0020] FIG. 4G, 4H, 4I, 4J, 4K, and 4L illustrate exemplary transimpedance measurements associated with a recipient over time, according to certain embodiments described herein. [0021] FIG.5 illustrates a lattice model that models current conduction through a fibrosis layer and through the perilymph and cochlear structures, according to certain embodiments described herein. [0022] FIGs. 6A, 6B, 6C, 6D, 6E, 6F, 6G, and 6H show exemplary graphs illustrating the lattice model parameters and measurements associated with a single layer model and a dual layer model, according to certain embodiments described herein. [0023] FIG.7 is a flow diagram illustrating a method of estimating an amount of fibrosis along a length of an electrode array. [0024] FIG. 8 is a flow diagram illustrating a method of identifying an amount of fibrosis at one or more electrodes of an electrode array. [0025] FIG.9 is a flow diagram illustrating a method of identifying an amount of fibrosis along a length of an electrode array. [0026] FIG.10 is a flow diagram illustrating a method of estimating fibrosis at one or more of a plurality of electrodes.
Atty. Docket No.3065.0754i Client Ref. No. CID03744WOPC1 [0027] FIG. 11 is a schematic diagram illustrating a vestibular stimulator system with which aspects of the techniques presented herein can be implemented; and. [0028] FIG. 12 is a schematic diagram illustrating a retinal prosthesis system with which aspects of the techniques presented herein can be implemented. DETAILED DESCRIPTION [0029] Presented herein are techniques for estimating the degree of fibrosis forming around one or more electrodes of an implantable stimulating/electrode array and using the estimate to set/adjust one or more operation parameters/settings of an implantable medical device that includes the electrode array (e.g., configure operation of the implantable medical device based on the degree of fibrosis). After implantation of the electrode array in, for example, the inner ear of a recipient, the recipient’s body/tissue reacts (e.g., the recipient’s body attempts to isolate the implant from the tissue), resulting in a connective tissue encapsulation/sheath that forms around the electrodes. This connective tissue growth is referred to as “fibrosis,” and the degree of fibrosis can vary from mild to severe, where in severe cases the scala tympani is substantially filled with connective tissue. In some cases, there can be even ossification along part of the electrode. [0030] The encapsulation of the electrodes can lead to higher tissue impedances and clinical impedances in general that potentially change over a period of time. For example, as the fibrosis occurs following implantation, the impedances can increase and the increased impedances can, in turn, affect the delivery of electrical stimulation to the recipient (e.g., initial stimulation parameters set at a first point in may not be appropriate at a later point in time, given the increased impedances). [0031] Conventional techniques exist to determine a “total” impedance associated with one electrodes, but fail to adequately account for (e.g., model) how fibrosis affects the total impedance and, in turn, how the fibrosis ultimately affects electrical stimulation parameters. More specifically, conventional techniques model the “total” impedance as comprising a “contact” impedance and a separate “tissue” impedance. However, the tissue impedance is a combination of a “fibrosis layer” impedance and the “far-field” impedance (e.g., perilymph and cochlear tissue impedance). By failing to separate out the of fibrosis layer impedance from the far-field impedance, conventional techniques fail to provide an accurate understand of how fibrosis affects the total impedance. That is, conventional techniques lack the granularity needed to fully understand the total impedance.
Atty. Docket No.3065.0754i Client Ref. No. CID03744WOPC1 [0032] As such, presented herein are techniques for modeling the total impedance by adding an additional circuit layer to model the fibrosis layer separately from the far-field impedance. An amount of fibrosis formed around the electrode may be estimated based on the modeling. More specifically, as described in greater detail below, the techniques presented herein decompose the various components that make up the total impedance into: (1) contact impedance, consisting of the near-field resistance (Rn) and the polarization impedance, (2) the fibrosis layer impedance, and (3) the far-field impedance (e.g., perilymph and cochlear tissue impedance). According to techniques presented herein, each of these components is identified and described separately. Describing the components separately may be used for many applications, such as improved stimulation parameter control (e.g., setting stimulation parameters of an implantable medical device), analysis of the effectiveness of drug eluting electrodes, etc. [0033] There are a number of different types of devices in/with which embodiments of the present invention may be implemented. Merely for ease of description, the techniques presented herein are primarily described with reference to a specific device in the form of a cochlear implant system. However, it is to be appreciated that the techniques presented herein may also be partially or fully implemented by any of a number of different types of devices, including consumer electronic device (e.g., mobile phones), wearable devices (e.g., smartwatches), hearing devices, implantable medical devices, wearable devices, etc. consumer electronic devices, wearable devices (e.g., smart watches, etc.), etc. As such, a hearing device can be a device for use by a hearing-impaired person (e.g., hearing aids, middle ear auditory prostheses, bone conduction devices, direct acoustic stimulators, electro-acoustic hearing prostheses, auditory brainstem stimulators, bimodal hearing prostheses, bilateral hearing prostheses, dedicated tinnitus therapy devices, tinnitus therapy device systems, combinations or variations thereof, etc.), a device for use by a person with normal hearing (e.g., consumer devices that provide audio streaming, consumer headphones, earphones, and other listening devices), a hearing protection device, etc. In other examples, the techniques presented herein can be implemented by, or used in conjunction with, various implantable medical devices, such as visual devices (i.e., bionic eyes), sensors, pacemakers, drug delivery systems, defibrillators, functional electrical stimulation devices, catheters, seizure devices (e.g., devices for monitoring and/or treating epileptic events), sleep apnea devices, electroporation devices, etc. [0034] FIGs.1A-1D illustrates an example cochlear implant system 102 with which aspects of the techniques presented herein can be implemented. The cochlear implant system 102
Atty. Docket No.3065.0754i Client Ref. No. CID03744WOPC1 comprises an external component 104 that is configured to be directly or indirectly attached to the body of the user, and an internal/implantable component 112 that is configured to be implanted in or worn on the head of the user. In the examples of FIGs.1A-1D, the implantable component 112 is sometimes referred to as a “cochlear implant.” FIG. 1A illustrates the cochlear implant 112 implanted in the head 154 of a user, while FIG.1B is a schematic drawing of the external component 104 worn on the head 154 of the user. FIG.1C is another schematic view of the cochlear implant system 102, while FIG. 1D illustrates further details of the cochlear implant system 102. For ease of description, FIGs.1A-1D will generally be described together. [0035] In the examples of FIGs. 1A-1D, the external component 104 comprises a sound processing unit 106, an external coil 108, and generally, a magnet fixed relative to the external coil 108. The cochlear implant 112 includes an implantable coil 114, an implant body 134, and an elongate stimulating assembly 116 configured to be implanted in the user’s cochlea. In one example, the sound processing unit 106 is an off-the-ear (OTE) sound processing unit, sometimes referred to herein as an OTE component, which is configured to send data and power to the implantable component 112. In general, an OTE sound processing unit is a component having a generally cylindrically shaped housing 111 and which is configured to be magnetically coupled to the user’s head 154 (e.g., includes an integrated external magnet 150 configured to be magnetically coupled to an internal/implantable magnet 152 in the implantable component 112). The OTE sound processing unit 106 also includes an integrated external (headpiece) coil 108 (the external coil 108) that is configured to be inductively coupled to the implantable coil 114. [0036] It is to be appreciated that the OTE sound processing unit 106 is merely illustrative of the external devices that could operate with implantable component 112. For example, in alternative examples, the external component 104 may comprise a behind-the-ear (BTE) sound processing unit configured to be attached to, and worn adjacent to, the recipient’s ear. In general, a BTE sound processing unit comprises a housing that is shaped to be worn on the outer ear of the user and is connected to the separate external coil assembly via a cable, where the external coil assembly is configured to be magnetically and inductively coupled to the implantable coil 114. It is also to be appreciated that alternative external components could be located in the user’s ear canal, worn on the body, etc. [0037] Although the cochlear implant system 102 includes the sound processing unit 106 and the cochlear implant 112, as described below, the cochlear implant 112 can operate
Atty. Docket No.3065.0754i Client Ref. No. CID03744WOPC1 independently from the sound processing unit 106, for at least a period, to stimulate the user. For example, the cochlear implant 112 can operate in a first general mode, sometimes referred to as an “external hearing mode,” in which the sound processing unit 106 captures sound signals which are then used as the basis for delivering stimulation signals to the user. The cochlear implant 112 can also operate in a second general mode, sometimes referred as an “invisible hearing” mode, in which the sound processing unit 106 is unable to provide sound signals to the cochlear implant 112 (e.g., the sound processing unit 106 is not present, the sound processing unit 106 is powered-off, the sound processing unit 106 is malfunctioning, etc.). As such, in the invisible hearing mode, the cochlear implant 112 captures sound signals itself via implantable sound sensors and then uses those sound signals as the basis for delivering stimulation signals to the user. Further details regarding operation of the cochlear implant 112 in the external hearing mode are provided below, followed by details regarding operation of the cochlear implant 112 in the invisible hearing mode. It is to be appreciated that reference to the external hearing mode and the invisible hearing mode is merely illustrative and that the cochlear implant 112 could also operate in alternative modes. [0038] In FIGs.1A and 1C, the cochlear implant system 102 is shown with an external device 110, configured to implement aspects of the techniques presented. The external device 110, which is shown in greater detail in FIG.1E, is a computing device, such as a personal computer (e.g., laptop, desktop, tablet), a mobile phone (e.g., smartphone), remote control unit, etc. The external device 110 and the cochlear implant system 102 (e.g., sound processing unit 106 or the cochlear implant 112) wirelessly communicate via a bi-directional communication link 126. The bi-directional communication link 126 may comprise, for example, a short-range communication, such as Bluetooth link, Bluetooth Low Energy (BLE) link, a proprietary link, etc. [0039] Returning to the example of FIGs.1A-1D, the sound processing unit 106 of the external component 104 also comprises one or more input devices configured to capture and/or receive input signals (e.g., sound or data signals) at the sound processing unit 106. The one or more input devices include, for example, one or more sound input devices 118 (e.g., one or more external microphones, audio input ports, telecoils, etc.), one or more auxiliary input devices 128 (e.g., audio ports, such as a Direct Audio Input (DAI), data ports, such as a Universal Serial Bus (USB) port, cable port, etc.), and a short-range wireless transmitter/receiver (wireless transceiver) 120 (e.g., for communication with the external device 110), each located in, on or near the sound processing unit 106. However, it is to be appreciated that one or more input
Atty. Docket No.3065.0754i Client Ref. No. CID03744WOPC1 devices may include additional types of input devices and/or less input devices (e.g., the short- range wireless transceiver 120 and/or one or more auxiliary input devices 128 could be omitted). [0040] The sound processing unit 106 also comprises the external coil 108, a charging coil, a closely-coupled radio frequency transmitter/receiver (RF transceiver) 122, at least one rechargeable battery 132, and an external sound processing module 124. The external sound processing module 124 can be configured to perform a number of operations which are represented in FIG.1D by a current spread measurement module 131, a sound processor 133, and a fibrosis detection module 135. Each of the current spread measurement module 131, the sound processor 133, and the fibrosis detection module 135 can be formed by one or more processors (e.g., one or more Digital Signal Processors (DSPs), one or more uC cores, etc.), firmware, software, etc. arranged to perform operations described herein. That is, the current spread measurement module 131, the sound processor 133, and the fibrosis detection module 135 can each be implemented as firmware elements, partially or fully implemented with digital logic gates in one or more application-specific integrated circuits (ASICs), partially or fully in software, etc. Although FIG. 1D illustrates the current spread measurement module 131, a sound processor 133, and a fibrosis detection module 135 as being implemented/performed at the external sound processing module 124, it is to be appreciated that these elements (e.g., functional operations) could also or alternatively be implemented/performed as part of the implantable sound processing module 158, as part of the external device 110, etc. [0041] Returning to the example of FIGs. 1A-1D, the implantable component 112 comprises an implant body (main module) 134, a lead region 136, and the intra-cochlear stimulating assembly 116, all configured to be implanted under the skin (tissue) 115 of the user. The implant body 134 generally comprises a hermetically-sealed housing 138 that includes, in certain examples, at least one power source 125 (e.g., one or more batteries, one or more capacitors, etc.) 125, in which RF interface circuitry 140 and a stimulator unit 142 are disposed. The implant body 134 also includes the internal/implantable coil 114 that is generally external to the housing 138, but which is connected to the RF interface circuitry 140 via a hermetic feedthrough (not shown in FIG.1D). [0042] As noted, stimulating assembly 116 is configured to be at least partially implanted in the user’s cochlea. Stimulating assembly 116 includes a plurality of longitudinally spaced intra-cochlear electrical stimulating contacts (electrodes) 144 that collectively form a contact array (electrode array) 146 for delivery of electrical stimulation (current) to the recipient’s
Atty. Docket No.3065.0754i Client Ref. No. CID03744WOPC1 cochlea. Stimulating assembly 116 extends through an opening in the recipient’s cochlea (e.g., cochleostomy, the round window, etc.) and has a proximal end connected to stimulator unit 142 via lead region 136 and a hermetic feedthrough (not shown in FIG.1D). Lead region 136 includes a plurality of conductors (wires) that electrically couple the electrodes 144 to the stimulator unit 142. The implantable component 112 also includes an electrode outside of the cochlea, sometimes referred to as the extra-cochlear electrode (ECE) 139. [0043] As noted, the cochlear implant system 102 includes the external coil 108 and the implantable coil 114. The external magnet 150 is fixed relative to the external coil 108 and the internal/implantable magnet 152 is fixed relative to the implantable coil 114. The external magnet 150 and the internal/implantable magnet 152 fixed relative to the external coil 108 and the internal/implantable coil 114, respectively, facilitate the operational alignment of the external coil 108 with the implantable coil 114. This operational alignment of the coils enables the external component 104 to transmit data and power to the implantable component 112 via a closely-coupled wireless link 148 formed between the external coil 108 with the implantable coil 114. In certain examples, the closely-coupled wireless link 148 is a radio frequency (RF) link. However, various other types of energy transfer, such as infrared (IR), electromagnetic, capacitive, and inductive transfer, may be used to transfer the power and/or data from an external component to an implantable component and, as such, FIG. 1D illustrates only one example arrangement. [0044] As noted above, sound processing unit 106 includes the external sound processing module 124. The external sound processing module 124 is configured to process the received input audio signals (received at one or more of the input devices, such as sound input devices 118 and/or auxiliary input devices 128), and convert the received input audio signals into output control signals for use in stimulating a first ear of a recipient or user (i.e., the external sound processing module 124 is configured to perform sound processing on input signals received at the sound processing unit 106). Stated differently, the one or more processors (e.g., processing element(s) implementing firmware, software, etc.) in the external sound processing module 124 are configured to execute sound processing logic in memory to convert the received input audio signals into output control signals (stimulation signals) that represent electrical stimulation for delivery to the recipient. [0045] As noted, FIG. 1D illustrates an embodiment in which the external sound processing module 124 in the sound processing unit 106 generates the output control signals. In an alternative embodiment, the sound processing unit 106 can send less processed information
Atty. Docket No.3065.0754i Client Ref. No. CID03744WOPC1 (e.g., audio data) to the implantable component 112 and the sound processing operations (e.g., conversion of input sounds to output control signals 156) can be performed by a processor within the implantable component 112. [0046] In FIG. 1D, according to an example embodiment, output control signals (stimulation signals) are provided to the RF transceiver 122, which transcutaneously transfers the output control signals (e.g., in an encoded manner) to the implantable component 112 via external coil 108 and implantable coil 114. That is, the output control signals (stimulation signals) are received at the RF interface circuitry 140 via implantable coil 114 and provided to the stimulator unit 142. The stimulator unit 142 is configured to utilize the output control signals to generate electrical stimulation signals (e.g., current signals) for delivery to the user’s cochlea via one or more of the stimulating contacts (electrodes) 144. In this way, cochlear implant system 102 electrically stimulates the user’s auditory nerve cells, bypassing absent or defective hair cells that normally transduce acoustic vibrations into neural activity, in a manner that causes the recipient to perceive one or more components of the input audio signals (the received sound signals). [0047] As detailed above, in the external hearing mode the cochlear implant 112 receives processed sound signals from the sound processing unit 106. However, in the invisible hearing mode, the cochlear implant 112 is configured to capture and process sound signals for use in electrically stimulating the user’s auditory nerve cells. In particular, as shown in FIG.1D, an example embodiment of the cochlear implant 112 can include a plurality of implantable sound sensors 165(1), 165(2) that collectively form a sensor array 160, and an implantable sound processing module 158. Similar to the external sound processing module 124, the implantable sound processing module 158 may comprise, for example, one or more processors and a memory device (memory) that includes sound processing logic. The memory device may comprise any one or more of: Non-Volatile Memory (NVM), Ferroelectric Random Access Memory (FRAM), read only memory (ROM), random access memory (RAM), magnetic disk storage media devices, optical storage media devices, flash memory devices, electrical, optical, or other physical/tangible memory storage devices. The one or more processors are, for example, microprocessors or microcontrollers that execute instructions for the sound processing logic stored in memory device. [0048] In the invisible hearing mode, the implantable sound sensors 165(1), 165(2) of the sensor array 160 are configured to detect/capture input sound signals 166 (e.g., acoustic sound signals, vibrations, etc.), which are provided to the implantable sound processing module 158.
Atty. Docket No.3065.0754i Client Ref. No. CID03744WOPC1 The implantable sound processing module 158 is configured to convert received input sound signals 166 (received at one or more of the implantable sound sensors 165(1), 165(2)) into output control signals 156 for use in stimulating the first ear of a recipient or user (i.e., the implantable sound processing module 158 is configured to perform sound processing operations). Stated differently, the one or more processors (e.g., processing element(s) implementing firmware, software, etc.) in implantable sound processing module 158 are configured to execute sound processing logic in memory to convert the received input sound signals 166 into output control signals 156 that are provided to the stimulator unit 142. The stimulator unit 142 is configured to utilize the output control signals 156 to generate electrical stimulation signals (e.g., current signals) for delivery to the user’s cochlea, thereby bypassing the absent or defective hair cells that normally transduce acoustic vibrations into neural activity. [0049] It is to be appreciated that the above description of the so-called external hearing mode and the so-called invisible hearing mode are merely illustrative and that the cochlear implant system 102 could operate differently in different embodiments. For example, in one alternative implementation of the external hearing mode, the cochlear implant 112 could use signals captured by the sound input devices 118 and the implantable sound sensors 165(1), 165(2) of sensor array 160 in generating stimulation signals for delivery to the user. [0050] According to the techniques of the present disclosure, external sound processing module 124 may also include an inertial measurement unit (IMU) 170. The inertial measurement unit 170 is configured to measure the inertia of the user's head, that is, motion of the user's head. As such, inertial measurement unit 170 comprises one or more sensors 175 each configured to sense one or more of rectilinear or rotatory motion in the same or different axes. Examples of sensors 175 that may be used as part of inertial measurement unit 170 include accelerometers, gyroscopes, inclinometers, compasses, and the like. Such sensors may be implemented in, for example, micro electromechanical systems (MEMS) or with other technology suitable for the particular application. [0051] As also illustrated in FIG.1D, in certain examples, a second inertial measurement unit (IMU) 180 including one or more sensors 185 is incorporated into implantable sound processing module 158 of implant body 134. Second inertial measurement unit 180 may serve as an additional or alternative inertial measurement unit to inertial measurement unit 170 of external sound processing module 124. Like sensors 175, sensors 185 may each be configured to sense one or more of rectilinear or rotatory motion in the same or different axes. Examples
Atty. Docket No.3065.0754i Client Ref. No. CID03744WOPC1 of sensors 185 that may be used as part of inertial measurement unit 180 include accelerometers, gyroscopes, inclinometers, compasses, and the like. Such sensors may be implemented in, for example, micro electromechanical systems (MEMS) or with other technology suitable for the particular application. For hearing devices that include an implantable sound processing module, such as implantable sound processing module 158, that includes an IMU, such as IMU 180, the techniques presented herein may be implemented without an external processor. Accordingly, a hearing device that includes an implant body 134 and lacks an external component 104 may be configured to implement the techniques presented herein. [0052] FIG. 1E is a block diagram illustrating one example arrangement for an external computing device 110 configured to perform one or more operations in accordance with certain embodiments presented herein. As shown in FIG. 1E, in its most basic configuration, the external computing device 110 includes at least one processing unit 183 and a memory 184. The processing unit 183 includes one or more hardware or software processors (e.g., Central Processing Units) that can obtain and execute instructions. The processing unit 183 can communicate with and control the performance of other components of the external computing device 110. The memory 184 is one or more software or hardware-based computer-readable storage media operable to store information accessible by the processing unit 183. The memory 184 can store, among other things, instructions executable by the processing unit 183 to implement applications or cause performance of operations described herein, as well as other data. The memory 184 can be volatile memory (e.g., RAM), non-volatile memory (e.g., ROM), or combinations thereof. The memory 184 can include transitory memory or non-transitory memory. The memory 184 can also include one or more removable or non-removable storage devices. In examples, the memory 184 can include random access memory (RAM), read only memory (ROM), EEPROM (Electronically-Erasable Programmable Read-Only Memory), flash memory, optical disc storage, magnetic storage, solid state storage, or any other memory media usable to store information for later access. By way of example, and not limitation, the memory 184 can include wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, RF, infrared and other wireless media or combinations thereof. In certain embodiments, the memory 184 comprises current spread measurement logic 195 or other processing logic 196 that, when executed, enables the processing unit 183 to perform aspects of the techniques presented. For example, current spread measurement logic 195 may facilitate taking current spread measurements, such as transimpedance measurements,
Atty. Docket No.3065.0754i Client Ref. No. CID03744WOPC1 automatically or based on a recipient input. Current spread measurement logic 195 may communicate with one or more other internal or external processors (e.g., in the cloud) to identify, for example, an amount of fibrosis, an amount of growth of a fibrosis, a rate of growth of a fibrosis, etc. based on the current spread measurements. [0053] In the illustrated example of FIG. 1E, the external computing device 110 further includes a network adapter 186, one or more input devices 187, and one or more output devices 188. The external computing device 110 can include other components, such as a system bus, component interfaces, a graphics system, a power source (e.g., a battery), among other components. The network adapter 186 is a component of the external computing device 110 that provides network access (e.g., access to at least one network 189). The network adapter 186 can provide wired or wireless network access and can support one or more of a variety of communication technologies and protocols, such as ETHERNET, cellular, BLUETOOTH, near-field communication, and RF (Radiofrequency), among others. The network adapter 186 can include one or more antennas and associated components configured for wireless communication according to one or more wireless communication technologies and protocols. The one or more input devices 187 are devices over which the external computing device 110 receives input from a user. The one or more input devices 187 can include physically- actuatable user-interface elements (e.g., buttons, switches, or dials), a keypad, keyboard, mouse, touchscreen, and voice input devices, among other input devices that can accept user input. The one or more output devices 188 are devices by which the computing device 110 is able to provide output to a user. The output devices 188 can include, for example, a display 190 (e.g., a liquid crystal display (LCD)) and one or more speakers 191, among other output devices for presentation of visual or audible information to the recipient, a clinician, an audiologist, or other user. [0054] It is to be appreciated that the arrangement for the external computing device 110 shown in FIG. 1E is merely illustrative and that aspects of the techniques presented herein can be implemented at a number of different types of systems/devices including any combination of hardware, software, and/or firmware configured to perform the functions described herein. For example, the external computing device 110 can be a personal computer (e.g., a desktop or laptop computer), a hand-held device (e.g., a tablet computer), a mobile device (e.g., a smartphone), a surgical system, and/or any other electronic device having the capabilities to perform the associated operations described elsewhere herein.
Atty. Docket No.3065.0754i Client Ref. No. CID03744WOPC1 [0055] Operational parameters/settings of stimulating implantable medical devices/components, such as a cochlear implant, are affected by various different impedances that can collectively be referred to as a “total” impedance. As used herein, the “total” impedance is the ratio of the voltage required to drive 1 unit (ampere) of (monopolar) current through internal electronics, the electrode lead, an electrode into the recipient’s tissue (e.g., an intracochlear contact/lead into the cochlear tissue), and then back through one or more return electrodes (e.g., extracochlear electrodes) into the stimulator package. All components contribute some level of resistance and many can be modeled by discrete resistors, except for the platinum contacts/electrodes (intracochlear and extracochlear) and electronic condensators. Various techniques have been used to identify equivalent circuit models for pushing current through a platinum contact. The dominant models are a leaky capacitor model (a capacitor bridged by a resistor) and constant phase elements (CPE). [0056] Once the current is injected in the tissue, the current path from the intracochlear contact to the extracochlear contact is modeled. This is a 3D complex volume conduction, with complex anatomy and material. However, it has been shown that the cochlea can be approximated as a leaky one-dimensional tube (uncoiled cochlea). Given the embedding in dense bone, the injected current tends to spread out, flowing longitudinally. Only a fraction of the injected current leaves the cochlea, flowing out transversally. A lattice model (LM) has been used to model the impedance of the current from the intracochlear contact to the extracochlear contact. The lattice model consists of 22 sections in which every section models the segment between two consecutive contacts. In every section, the injected current can either flow to the left or the right or out of the cochlea. [0057] The model currently used to model TIM spread curves is a slight extension of the above- described lattice model. In the current single layer lattice model, for each of the positions of the current sources (i.e., each electrode contact), a local resistor is added to represent the resistive contact impedance (redox reaction) contribution when driving current through an intracochlear contact. The parameters of the lumped circuit model (22 transversal and 21 longitudinal resistors, so 43 degrees of freedom) can be estimated from a straightforward transimpedance matrix measurement. [0058] TIM measurements are current spread measurements that are used for several applications (e.g., for tip fold-over detection). The TIMs contain 22 x 22 = 484 values. Since the TIM is symmetric (on theoretical grounds), the number of free parameters in the
Atty. Docket No.3065.0754i Client Ref. No. CID03744WOPC1 measurement are 242. Approximating the TIM measurements with the lattice model produces a data reduction of a factor of 5.6 (=242/43). [0059] The analysis method consists of solving a multi-dimensional non-linear optimization problem and determining the best 43 resistor values that best match the observed in-vivo TIM. In its simplest form, the cost function to minimize is the root mean square error between the observed TIM and the model TIM. Some software tools offer various numerical solvers to tackle this problem. [0060] The method of analyzing/modeling the TIM measurements allows for opening up the “black box” to gain insight in the internal (electrical) state of the cochlea (one-dimensional tube) by performing an “external” system identification measurement (in: current, out: induced voltage). The details of every individual person’s TIM are different, reflecting their anatomy, electrode position, etc. By determining the local resistivity parameters, it is possible to gain insight into how the current is flowing, and how the current is leaving the cochlea. This has relevance for understanding electrode position (e.g., tip fold-over, translations, partial insertions, etc.), anatomy (e.g., cochlear malformation, facial nerve stimulation, etc.), etc. Currently, intraoperative TIMs are used for commercial purposes for determining tip fold-over and insertion angle, and modiolar proximity for electrode position. At lower TRL, various other applications of TIM may be used (e.g., facial nerve stimulation and fibrosis). [0061] Analyzing TIM matrices with the lattice model method works well on intracochlear TIM measurements taken during surgical procedures. The fitting error between the observed TIM and the modeled TIM is generally small (e.g., on the order of 1-5%). However, on post- operative TIM measurements, the lattice model method gives a poorer model fit. The growth of the fibrosis along the electrode array post-surgery may account for an increase in the fitting error between observed and modeled TIMs in the weeks or months after surgery. In other words, the fibrosis may not be accounted for using current lattice models and, therefore, as the fibrosis grows in the time after surgery, current lattice models may be less accurate. [0062] FIG.2A illustrates a post-operative TIM, while FIGs.2B and 2C each illustrate a model TIM that were generated based on lattice models (sometimes referred to herein as lattice model TIMs). Lattice model TIM 220, shown in FIG. 2B, illustrates a TIM generated based on a single layer lattice fit model, while lattice model TIM 230, shown in FIG.2C, illustrates a TIM generated based on a dual layer lattice model. The measured TIM 210 of FIG.2A is generated based on post-operative measurements of a recipient of a cochlear implant. As used herein,
Atty. Docket No.3065.0754i Client Ref. No. CID03744WOPC1 the term “single layer lattice model” refers to a lattice model with a layer representing a near- field impedance and a layer representing a tissue impedance. As used herein, the term “dual layer lattice model” refers to a lattice model with a layer representing the near-field impedance, a layer representing the perilymph/tissue impedance, and a layer representing the fibrosis impedance. [0063] Transimpedances are measured by means of 22 electrodes of an electrode array and show the propagation of current injected into the cochlea at different electrode positions. TIM 210 illustrates typical local rises in impedances near the stimulation contact. The impedance peaks in TIM 210 can be seen at the stimulation contact (i.e., the electrode where the current is injected). The impedance peaks are explained by the near-field effect. When current is injected at a platinum (Pt) electrode contact, very close to the Pt electrode contact (the vicinity), all current is concentrated in a very small volume, causing a rise of the voltage. Theoretically this can be modeled by a spheric voltage increase (point source radiating in open 3D space, falling off as 1/r2). Once stimulation of the electrodes starts, an additional voltage contribution will develop (polarization component) since the oxidation-reduction (redox) reactions driving current into the tissue require a voltage difference between the Pt contact and the perilymph. This is omitted here (measure at time 0). [0064] Typically for a post-operative TIM, the non-stimulation impedances registered on the two or three contacts to the apical and basal side of the injection contact are also elevated, which is harder to explain. There is no current concentration or electrochemical activity. When modeling this TIM with a lattice model, the model cannot follow these “local” impedance surges. For intra-operative data, it has been hypothesized that the local voltage increases are due to the electrode being very close to the modiolar wall. In fact, these local skirts are used as features in the modiolar proximity algorithm. [0065] However, in selected cases, it has been observed that these voltage bumps grow with time after implantation, indicating a dynamic ongoing process, such as fibrosis formation. In a recent study, applying lattice model analysis showed an increase on the near-field impedance (N) component with time. N is defined as the difference between the peak impedance (access resistance rA) and the far-field impedance (rF), obtained with a dual exponential curve, fitted to the spread function (essentially a variation on the lattice model fit). The single layer lattice model fit is not performing well in these cases. As shown in the TIM 220 of the single layer lattice model, the model accuracy is only 88% in this case, and the curve fits are underfitting the true voltage spread curves.
Atty. Docket No.3065.0754i Client Ref. No. CID03744WOPC1 [0066] The single layer lattice model does not account for the tissue sheath/fibrosis layer that forms around the electrode. This layer is created by the immune system activity, resulting in a sheath of conductive tissue surrounding the electrode array. The conductivity of the tissue is quite different from highly conductive perilymph. From an electrical point of view, the ions formed at the contact surface will be contained in a small fluid layer between the array and the tissue sheath. In order to reach the auditory nerve and leave the cochlea, the monopolar current will have to cross the fibrosis layer. The resistivity depends on the thickness, density, and material of the fibrosis layer. In severe cases, this layer can become ossified. [0067] FIG. 3 illustrates a model 300 for a post-operative inner ear. As illustrated in FIG. 3, an electrode array 302 is surrounded by a layer of connective tissue 304 (fibrosis) and immersed in the perilymph 306 of the scala tympani. A width of the layer of connective tissue 304 may increase in the days, weeks, and months after surgery. For example, in the time post-surgery, the perilymph may grow as the recipient’s body reacts to the insertion of the electrode array. The width of the layer of the connective tissue 304 may vary along the length of the electrode array 302. [0068] FIGs. 4A-4L are each TIMs that collectively illustrate the evolution of impedances along an electrode array in a recipient over 12 months. In particular, 4A-4F illustrate examples in which all impedances are shown, while FIGs.4G-4L illustrate examples in which only the transimpedances are shown. In the graphs shown in FIGs.4A-4L the electrodes disposed along an electrode array are shown on the x-axis and the impedances are shown on the y-axis. For ease of description, FIGs.4A-4L will generally be described together. [0069] In these examples, TIM 402 illustrates the measurements taken on a recipient during surgery, TIM 404 illustrates the measurements taken at activation (4 weeks after surgery), TIM 406 illustrates the measurements taken one month after activation, TIM 408 illustrates the measurements taken 3 months after activation, TIM 410 illustrates the measurements taken 6 months after activation, and TIM 412 illustrates the measurements taken 12 months after activation. As illustrated in FIGs. 4A-4F, the impedances along the electrode array increase after surgery due to the growth of a layer of tissue or fibrosis along the electrode. For example, TIM 402 shows that the impedance at electrode 13 is between 5 and 6 kOhms at the time of the surgery. However, by month 3, TIM 408 illustrates that the impedance at electrode 13 is 8 kOhm and, at month 12, TIM 412 shows that the impedance at electrode 13 is nearly 12 kOhmn. The increase in the impedances may be attributable to a growth of the fibrosis at electrode 13 (and other points along the electrode array).
Atty. Docket No.3065.0754i Client Ref. No. CID03744WOPC1 [0070] Similarly, turning to FIGs. 4G-4L, TIM 420 illustrates the measurements taken on a recipient during surgery, TIM 422 illustrates the measurements taken at activation (4 weeks after surgery), TIM 424 illustrates the measurements taken one month after activation, TIM 426 illustrates the measurements taken 3 months after activation, TIM 428 illustrates the measurements taken 6 months after activation, and TIM 430 illustrates the measurements taken 12 months after activation. As illustrated in FIGs. 4G-4L, the transimpedances along the electrode array increase after surgery due to the growth of a layer of tissue or fibrosis along the electrode. [0071] As described above, a single layer lattice model may be used to model the contact impedance and the tissue impedance associated with the TIM measurements. To account for the growth of tissue or fibrosis that grows along the electrode, embodiments described herein provide for adding a second layer representing the fibrosis impedance to create a dual layer lattice model with its own transversal (crossing the barrier) and longitudinal (flowing along the electrode array) conduction pathways. In particular, as described elsewhere herein, the dual layer lattice model is able to decompose the various components that make up the total impedance into: (1) contact impedance, consisting of the near-field resistance (Rn) and the polarization impedance, (2) the fibrosis layer impedance, and (3) the far-field impedance (e.g., perilymph and cochlear tissue impedance). As described elsewhere herein, the resulting data can, in turn, be used to set/adjust one or more settings/parameters of the implantable medical device. [0072] FIG. 5 illustrates a dual layer lattice model 500 that models a current conduction through a fibrosis layer and through the perilymph and cochlear structures. Lattice model 500 includes layer 502 with resistors N modeling the impedance at the injection point of the current, layer 504 with transverse resistors t and longitudinal resistors l modeling the impedance through the fibrosis, and layer 506 with transverse resistors T and longitudinal resistors L modeling the impedance through the perilymph and cochlear structures. [0073] In lattice model 500, a current source 508 injects current in the cochlea (e.g., at electrode 3). The current spreads out through the network, representing the current sinks, to extracochlear electrodes. The resistor values of the lattice model 500 represent the impedance associated with the current as the current first flows through the fibrosis layer and then is injected into the tissue/perilymph. Lattice model 500 is a portion of a lattice model that represents an entire electrode array. Although lattice model 500 illustrates six transverse
Atty. Docket No.3065.0754i Client Ref. No. CID03744WOPC1 resistors and five longitudinal resistors for each layer, a lattice model representing an entire electrode array includes 22 transverse resistors and 21 longitudinal resistors for each layer. [0074] Mathematically, the extension to the lattice model to include layer 504 does not fundamentally change the underlying equations associated with previous lattice models. Given a set of resistor values for all components in the equivalent circuit, it is possible to calculate the corresponding TIM matrix at the level of the injection points of the current (resistors N). This is the model TIM. An approximation error (cost function) can be calculated, and the error can be minimized using non-linear multidimensional solvers. [0075] Practically, the solution is more complicated. A practical approach includes first modeling the TIM with a single layer lattice model (22 transverse resistor values (T) and 21 longitudinal resistor values (L) as unknowns). In this phase, the peak values are omitted from the optimization problem and only the errors to the off-diagonal values are considered. A regularization term is included on the transversal and longitudinal values to minimize erratic differences. The single layer model is used to seed the optimization of the dual lattice model. Again, only the tails (off-diagonal values) are considered in the optimization problem. Based on the optimal dual lattice model, the near-field resistor values (N) in layer 502 are added to model the peak impedances. [0076] Returning to FIGs. 2A-2C, lattice model TIM 230 illustrates the TIM associated with the dual layer lattice model fit. As can be seen in FIG. 2C, lattice model TIM 230 fits the observed data shown by TIM 210 better than the single layer lattice model illustrated by TIM 220. In fact, the model accuracy increases from 88% to 97.7% by including the additional fibrosis layer in the lattice model. The addition of the fibrosis layer in the lattice model allows the model to also capture the local impedance rise. [0077] FIGs. 6A-6H are graphs illustrating the lattice model parameters for the single layer model and the dual layer model for the example illustrated in FIGs.2A-2C. More specifically, in graphs 602, 604, 608, and 610, the dotted line represents parameters of a single layer model, and the solid line represents parameters of the dual layer model. The x-axes of the graphs show the electrodes of an electrode array and the y-axes show the corresponding resistor value at each electrode in the lattice model. [0078] Graph 602 illustrates the “bulk” or near-field resistor values (N) for the single layer lattice model and the dual layer lattice model. Graph 604 illustrates the transverse resistor values for the fibrosis layer (e.g., layer 504 in FIG.5) and graph 606 illustrates the values for
Atty. Docket No.3065.0754i Client Ref. No. CID03744WOPC1 the longitudinal resistors in the fibrosis layer. The transverse and longitudinal resistor values for the fibrosis layer are zero for the single layer model because the single layer model does not include the fibrosis layer. Graph 608 illustrates the values for the transverse resistor values for the tissue/perilymph layer (e.g., layer 506 in FIG. 5) and graph 610 illustrates the longitudinal resistor values for the tissue/perilymph layer. [0079] Graph 612 illustrates a corresponding model TIM for a single layer model. The spread curves capture the far-field tails well. The average impedance at the current injection point is +/- 1.5 kOhm. Together, graphs 614 and 616 show the contributing parts of the dual layer model, whose total TIM is TIM 230 of FIG. 2C. In particular, graph 614 shows the further tuning of the “perilymph network.” In other words, graph 614 illustrates tissue/perilymph contribution to TIM 230. [0080] Graph 616 illustrates the “fibrosis network” or the fibrosis contribution to the TIM 230. Very different exponential length constants are shown in graph 616. The fibrosis network spreads the current out over 2-3 electrodes to the left and right of the injection contact. The current spread is fairly compact. The current leaving the fibrosis network is then injected in the perilymph network with very wide length constants, almost covering the complete implanted cochlea length. [0081] By analyzing the impedance graph, the thickness of the fibrosis around the electrodes may be determined. As shown in graph 616, the impedance around electrodes 3 and 4 is high. The impedances in graph 616 illustrate the impedance of the current traveling through the fibrosis layer at each electrode before the current is injected in the perilymph (and cochlea tissue). A high impedance indicates a thicker layer of fibrosis growing at a particular electrode. For example, the high impedance values at electrodes 3 and 4 indicate that the fibrosis around electrodes 3 and 4 is thicker than around other electrodes. The impedance at electrode 12 is the lowest, indicating that the fibrosis layer is thinnest near electrode 12. As discussed further below, identifying the thickness of the fibrosis layer is helpful for determining cochlear health and for a number of other applications. [0082] By comparing TIM measurements for a recipient over time, an amount of fibrosis along a length of an electrode array may be identified and a growth of the fibrosis layer may be monitored. For example, the growth of the fibrosis may be identified by determining the delta between two TIMs taken at different times. In addition, the contribution of the fibrosis to the TIM measurements may be determined using a multi-layer model, such as a dual layer lattice
Atty. Docket No.3065.0754i Client Ref. No. CID03744WOPC1 model or another type of model, to isolate the impedances attributable to the fibrosis and estimate an amount of fibrosis at one or more electrodes in the array of electrodes. [0083] In the general, the electrode array used to obtain the TIM measurements is a component of an implantable medical device. As described elsewhere herein, operation of the implantable medical device (e.g., settings/parameters of the implantable medical device) can be configured (e.g., in an automated or semi-automated manner) based on the amount of the fibrosis. [0084] Although lattice models have been discussed herein, other types of models may be used for identifying the fibrosis layer around the electrodes. For example, a lumped model may be used in which the contact impedance parts are a constant phase element (CPE) or a resistor- capacitor (RC) circuit, the fibrosis layer is a lattice network of resistors, and the tissue/perilymph model is also a lattice network. In addition, the lattice network of resistors may include charge storage elements (e.g., capacitors and other charge storage mechanisms). The charge storage elements can be used to model, for example, cell adhesion, the contact itself, a “double layer” where charge is stored in a layer of ions in the fluid and electrons in the Pt metallic layer, etc. As another example of a type of model, in a high-resolution version, the model may consist of three-dimensional personalized anatomical models (e.g., from a CT), where the electrode array is surrounded by a fibrous tissue layer with unknown size and unknown density, with a thickness of the fibrous tissue layer varying along the length of the electrode array. [0085] Embodiments described herein provide a viable biomarker for fibrosis formation. The results can be determined from in-vivo measurements that do not take long. For example, the measurement may be taken in just a few minutes. The measurements should be taken during the initial implantation surgery and in every clinic visit thereafter to monitor the growth of the fibrosis. The measurements may also be taken by a recipient of a hearing device using an application on an external device. [0086] The post-analysis of the measurements to extract the fibrosis component may also be performed quickly. For example, the computation may take less than a minute on a standard computer. Therefore, the post-analysis can be integrated in intra-operative software or post- operative software, both in the clinic or even at home. The computations may also be performed using software stored on an external storage (e.g., cloud storage). [0087] A robust user interface may be used for clinician applications. In one embodiment, a categorization algorithm may be developed to classify the degree of fibrosis (e.g., as mild,
Atty. Docket No.3065.0754i Client Ref. No. CID03744WOPC1 moderate, or severe, and, in some cases, ossification). For such a classifier to be designed, machine learning approaches may be used based on large data sets associated with recipients of hearing devices. The classification may be cochlea-wide or may be specific to a cochlear region (e.g., severe-at-the-base, while mild-at-the-tip). [0088] The identification of fibrosis biomarkers may be useful in a number of ways. For example, monitoring the fibrosis formation may be helpful for monitoring the cochlear health of a recipient. As another example, data associated with the growth of the fibrosis may be used as an outcome metric for the effectiveness of drug eluting electrodes, possibly helping with fine tuning dosage and elution. The fibrosis growth data may additionally be used for monitoring and intervention for preserving residual hearing, prediction of stimulation levels (T/C), automation of focused channel configuration (e.g., determine the degree of channel focusing), and audiological management of complex cases (e.g., cochlear malformations or facial nerve stimulation). In some embodiments, the amount of fibrosis or the growth of the fibrosis may be used to predict hearing outcomes associated with recipients and/or to set/adjust one or more parameters of an implantable medical device associated with the recipient. For example, a recipient with a lot of fibrosis may obtain worse hearing outcomes than a recipient with less fibrosis growth. [0089] The dual layer lattice model may be used for monitoring other areas of the body. For example, a single layer lattice model may be insufficient for modeling a facial nerve stimulation TIM dataset. In this example, the path predictions with a single layer model may not be enough for a Function Neurological Symptoms (FNS) diagnosis. In this case, using the dual layer model that accounts for fibrosis formation provides more and better information to make diagnoses. In general, a metric that considers the fibrosis process is useful in every situation where a post-operative TIM needs to be analyzed. [0090] The TIM measurements play a crucial role throughout a recipient’s journey. For example, during surgery, the application of the TIM measurements may be used for monitoring insertion and supporting preservation of residual hearing, such as while performing electrocochleography. The TIM measurements are additionally used to verify the correct placement of the electrode (e.g., insertion angle, modiolar proximity, tip fold-over, partial insertion, translocation, etc.). Each of these use cases requires a slightly different decision algorithm, running on top of TIM.
Atty. Docket No.3065.0754i Client Ref. No. CID03744WOPC1 [0091] Post-operative, the TIM measurements are used in-clinic to assist audiologists in diagnosing the implanted cochlea, fitting the hearing device, and monitoring cochlear health. Adding the fibrosis layer to the lattice module may be useful for managing complex cases. Currently, integrity management is limited to determining short and open circuits. However, tip fold-over detection, facial nerve case management, partial insertions, etc., may be added to integrity management. Identifying fibrosis growth may play a role in the integrity management. [0092] TIM is foundational for the channel configuration in focused multipolar strategies. In the current research approach, the channel weights are recalculated at every clinic visit. The use cases that require regular monitoring (e.g., residual hearing) will require that the measurement be initiated by the user in the home environment or is fully automated in the sound processor. Embodiments described herein provide for initiating the measurements using an external device or automating the measurements in the sound processor. In addition, embodiments described herein may be used for predicting or setting a "channel definition" based on the amount of fibrosis. For example, if a stimulation channel has one parameter (e.g., the defocusing index), the amount of the fibrosis or the growth of the fibrosis over time may be used to determine how to set this focus degree and when to recalculate the channel definition. As such, an optimal stimulation channel definition may be predicted based on the amount of the fibrosis or the growth of the fibrosis. That is, one or more settings/parameters of an implantable medical device (e.g., cochlear implant, vestibular implant, etc.) can be set/adjusted based on the amount of the fibrosis. [0093] FIG.7 is a flow diagram illustrating a method 700 of estimating an amount of fibrosis along a length of an electrode array. At 702, TIM measurements are performed in response to stimulation of an electrode array implanted in a region of an inner ear of a recipient. At 704, the TIM measurements are analyzed with a multi-layer model. The multi-layer model includes a first layer representing a contact impedance, a second layer representing impedance associated with a fibrosis along the electrode array, and a third layer representing impedance associated with the inner ear region. At 706, an amount of the fibrosis along a length of the electrode array is estimated based on the multi-layer model. The electrode array is a component of an implantable medical device and, in certain aspects, the method 700 includes setting/adjusting one or more operational settings/parameters of the implantable medical device based on the amount of the fibrosis along a length of the electrode array, as estimated based on the multi-layer model.
Atty. Docket No.3065.0754i Client Ref. No. CID03744WOPC1 [0094] FIG.8 is a flow diagram illustrating a method 800 of identifying an amount of fibrosis at one or more electrodes of an electrode array. At 802, measurements (e.g., current spread measurements) associated with an electrode array implanted in a recipient (e.g., in an inner ear or other body chamber of the recipient) are obtained. At 804, a model is constructed based on the measurements. The model indicates impedances associated with an electrode-tissue interface, impedances associated with a fibrosis along the electrode array, and impedances associated with body fluid (e.g., perilymph) of the recipient. At 806, an amount of the fibrosis at one or more electrodes of the electrode array is identified from the model. The electrode array is a component of an implantable medical device and, in certain aspects, the method 800 includes setting/adjusting one or more operational settings/parameters of the implantable medical device based on the amount of the fibrosis at one or more electrodes of the electrode array, as is identified from the model. [0095] FIG.9 is a flow diagram illustrating a method 900 of identifying an amount of fibrosis along a length of an electrode array. At 902, a plurality of TIM measurements associated with an electrode array implanted in a cochlea of a recipient over a period of time are obtained. At 904, an amount of fibrosis along a length of the electrode array is identified based on the plurality of TIM measurements. The electrode array is a component of an implantable medical device and, in certain aspects, the method 900 includes setting/adjusting one or more operational settings/parameters of the implantable medical device based on the amount of the fibrosis at one or more electrodes of the electrode array, as is identified based on the plurality of TIM measurements. [0096] FIG. 10 is a flow diagram illustrating a method 1000 of estimating fibrosis at one or more of a plurality of electrodes. At 1002, a plurality of measurements representing current spread from a plurality of electrodes in an inner ear of a recipient is obtained. At 1004, the plurality of measurements are analyzed with a multi-layer model to estimate fibrosis at one or more of the plurality of electrodes. The plurality of electrodes are part of an implantable medical device and, in certain aspects, the method 1000 includes setting/adjusting one or more operational settings/parameters of the implantable medical device based on the fibrosis at one or more of the plurality of electrodes, as estimated using the multi-layer model. [0097] The system and techniques described herein have primarily been described with reference to the use of Time Varying Impedances or Trans Impedance Matrixes (TIM)s. However, it is to be appreciated that, as used herein, the term “impedances” is not limited to use of TIMs, but can also include the use of the types of impedance measurements/impedance
Atty. Docket No.3065.0754i Client Ref. No. CID03744WOPC1 values, including one or more of Common Ground Impedances, Monopolar Impedances (e.g., MP1, MP2), Four Point Impedances, in addition to, or as alternative to, TIMs. For completeness, these different impedance measurements are each described briefly below. [0098] “Common Ground Impedance”: In the common ground mode, current is applied and voltage is measured between a single intracochlear electrode and all other intracochlear electrodes shorted together. [0099] “Monopolar Impedance” (MP1 or MP2): This impedance measurement mode stimulates and records from an individual intracochlear electrode that is grounded to the two extracochlear grounds (i.e., the pin and case grounds). This is measured at one time point at the end of the stimulating pulse, which encapsulates all elements of impedance. [00100] “Four Point Impedance”: Four-point impedance is measured by utilizing four intracochlear electrodes. When four-point impedance is measured, current is applied between two of the electrodes while measuring the voltage differential between the other two electrodes. For example, the current may be driven between electrodes 3 and 10 and the voltage differential may be measured between electrodes 4 and 9. The four electrodes can run from basal to apical ends of the electrode array to provide frequency-specific electrophysiological information along the cochlea. [00101] “Time Varying Impedance” / “Trans Impedance Matrix” (TIM): Trans impedance matrices are measured in the same mode as monopolar (MP1+2) described above. It expands the information collected by assessing impedance at numerous time points during the pulse. This allows the impedance measures to be analyzed into sub-components of “access impedance” and “polarization impedance.” [00102] As previously described, the technology disclosed herein can be applied in any of a variety of circumstances and with a variety of different devices. Example devices that can benefit from technology disclosed herein are described in more detail in FIGS.11 and 12. The techniques of the present disclosure can be applied to other devices, such as neurostimulators, cardiac pacemakers, cardiac defibrillators, sleep apnea management stimulators, seizure therapy stimulators, tinnitus management stimulators, and vestibular stimulation devices, as well as other medical devices that deliver stimulation to tissue. Further, technology described herein can also be applied to consumer devices. These different systems and devices can benefit from the technology described herein.
Atty. Docket No.3065.0754i Client Ref. No. CID03744WOPC1 [00103] FIG. 11 illustrates an example vestibular stimulator system 1102, with which embodiments presented herein can be implemented. As shown, the vestibular stimulator system 1102 comprises an implantable component (vestibular stimulator) 1112 and an external device/component 1104 (e.g., external processing device, battery charger, remote control, etc.). The external device 1104 comprises a transceiver unit 1160. As such, the external device 1104 is configured to transfer data (and potentially power) to the vestibular stimulator 1112. [00104] The vestibular stimulator 1112 comprises an implant body (main module) 1134, a lead region 1136, and a stimulating assembly 1116, all configured to be implanted under the skin/tissue (tissue) 1115 of the recipient. The implant body 1134 generally comprises a hermetically-sealed housing 1138 in which RF interface circuitry, one or more rechargeable batteries, one or more processors, and a stimulator unit are disposed. The implant body 134 also includes an internal/implantable coil 1114 that is generally external to the housing 1138, but which is connected to the transceiver via a hermetic feedthrough (not shown). [00105] The stimulating assembly 1116 comprises a plurality of electrodes 1144(1)-(3) disposed in a carrier member (e.g., a flexible silicone body). In this specific example, the stimulating assembly 1116 comprises three (3) stimulation electrodes, referred to as stimulation electrodes 1144(1), 1144(2), and 1144(3). The stimulation electrodes 1144(1), 1144(2), and 1144(3) function as an electrical interface for delivery of electrical stimulation signals to the recipient’s vestibular system. [00106] The stimulating assembly 1116 is configured such that a surgeon can implant the stimulating assembly adjacent the recipient’s otolith organs via, for example, the recipient’s oval window. It is to be appreciated that this specific embodiment with three stimulation electrodes is merely illustrative and that the techniques presented herein may be used with stimulating assemblies having different numbers of stimulation electrodes, stimulating assemblies having different lengths, etc. [00107] In operation, the vestibular stimulator 1112, the external device 1104, and/or another external device, can be configured to implement the techniques presented herein. That is, the vestibular stimulator 1112, possibly in combination with the external device 1104 and/or another external device, can include an evoked biological response analysis system, as described elsewhere herein. [00108] FIG. 12 illustrates a retinal prosthesis system 1201 that comprises an external device 1210 (which can correspond to a wearable device) configured to communicate with an
Atty. Docket No.3065.0754i Client Ref. No. CID03744WOPC1 implantable retinal prosthesis 1200 via signals 1251. The retinal prosthesis 1200 comprises an implanted processing module 1225 and a retinal prosthesis sensor-stimulator 1290 is positioned proximate the retina of a recipient. The external device 1210 and the processing module 1225 can communicate via coils 1208, 1214. [00109] In an example, sensory inputs (e.g., photons entering the eye) are absorbed by a microelectronic array of the sensor-stimulator 1290 that is hybridized to a glass piece 1292 including, for example, an embedded array of microwires. The glass can have a curved surface that conforms to the inner radius of the retina. The sensor-stimulator 1290 can include a microelectronic imaging device that can be made of thin silicon containing integrated circuitry that convert the incident photons to an electronic charge. [00110] The processing module 1225 includes an image processor 1223 that is in signal communication with the sensor-stimulator 1290 via, for example, a lead 1288 which extends through surgical incision 1289 formed in the eye wall. In other examples, processing module 1225 is in wireless communication with the sensor-stimulator 1290. The image processor 1223 processes the input into the sensor-stimulator 1290, and provides control signals back to the sensor-stimulator 1290 so the device can provide an output to the optic nerve. That said, in an alternate example, the processing is executed by a component proximate to, or integrated with, the sensor-stimulator 1290. The electric charge resulting from the conversion of the incident photons is converted to a proportional amount of electronic current which is input to a nearby retinal cell layer. The cells fire and a signal is sent to the optic nerve, thus inducing a sight perception. [00111] The processing module 1225 can be implanted in the recipient and function by communicating with the external device 1210, such as a behind-the-ear unit, a pair of eyeglasses, etc. The external device 1210 can include an external light / image capture device (e.g., located in / on a behind-the-ear device or a pair of glasses, etc.), while, as noted above, in some examples, the sensor-stimulator 1290 captures light / images, which sensor-stimulator is implanted in the recipient. [00112] As should be appreciated, while particular uses of the technology have been illustrated and discussed above, the disclosed technology can be used with a variety of devices in accordance with many examples of the technology. The above discussion is not meant to suggest that the disclosed technology is only suitable for implementation within systems akin to that illustrated in the figures. In general, additional configurations can be used to practice
Atty. Docket No.3065.0754i Client Ref. No. CID03744WOPC1 the processes and systems herein and/or some aspects described can be excluded without departing from the processes and systems disclosed herein. [00113] This disclosure described some aspects of the present technology with reference to the accompanying drawings, in which only some of the possible aspects were shown. Other aspects can, however, be embodied in many different forms and should not be construed as limited to the aspects set forth herein. Rather, these aspects were provided so that this disclosure was thorough and complete and fully conveyed the scope of the possible aspects to those skilled in the art. [00114] As should be appreciated, the various aspects (e.g., portions, components, etc.) described with respect to the figures herein are not intended to limit the systems and processes to the particular aspects described. Accordingly, additional configurations can be used to practice the methods and systems herein and/or some aspects described can be excluded without departing from the methods and systems disclosed herein. [00115] According to certain aspects, systems and non-transitory computer readable storage media are provided. The systems are configured with hardware configured to execute operations analogous to the methods of the present disclosure. The one or more non-transitory computer readable storage media comprise instructions that, when executed by one or more processors, cause the one or more processors to execute operations analogous to the methods of the present disclosure. [00116] Similarly, where steps of a process are disclosed, those steps are described for purposes of illustrating the present methods and systems and are not intended to limit the disclosure to a particular sequence of steps. For example, the steps can be performed in differing order, two or more steps can be performed concurrently, additional steps can be performed, and disclosed steps can be excluded without departing from the present disclosure. Further, the disclosed processes can be repeated. [00117] Although specific aspects were described herein, the scope of the technology is not limited to those specific aspects. One skilled in the art will recognize other aspects or improvements that are within the scope of the present technology. Therefore, the specific structure, acts, or media are disclosed only as illustrative aspects. The scope of the technology is defined by the following claims and any equivalents therein.
Atty. Docket No.3065.0754i Client Ref. No. CID03744WOPC1 [00118] It is also to be appreciated that the embodiments presented herein are not mutually exclusive and that the various embodiments may be combined with another in any of a number of different manners.