Background stimulation used to fit cochlear implant

Abstract

A fitting arrangement for fitting electrode contacts of a cochlear implant electrode array implanted in a cochlea of ​​an implanted patient is described. This includes: iteratively fitting a plurality of fitting electrode contacts by performing the following for each of the fitting electrode contacts: i. delivering a fitting stimulation signal to the fitting electrode contact and at least one adjacent electrode contact to stimulate adjacent auditory nerve tissue, wherein the fitting stimulation signal is characterized by a charge level distribution function having a non-zero noise level charge at at least one adjacent electrode contact and a response level charge that is much greater than the noise level charge at the fitting electrode contact; and ii. obtaining a patient response to the fitting stimulation signal from the implanted patient. Then, based on the patient response, a patient-specific fitting map is defined for the electrode contacts of the cochlear implant electrode array.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority from U.S. Provisional Patent Application No. 62 / 702,944, filed on July 25, 2018, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to hearing implant systems and, more particularly, to custom fitting of hearing implant systems such as cochlear implants. Background Art

[0004] Normal ears Figure 1 The sound is transmitted to the eardrum (tympanic membrane) 102 through the outer ear 101, and the eardrum vibrates the ossicles (malleus, incus and stapes) of the middle ear 103. The stapes footplate is positioned in the oval window 106, which forms an interface with the inner ear (cochlea) 104 filled with fluid. The movement of the stapes generates pressure waves in the cochlea 104, which stimulate the sensory cells (hair cells) of the auditory system. The cochlea 104 is a long narrow conduit that is spirally wound about two and a half turns around its central axis (called the modiolus). The cochlea 104 includes an upper channel called the vestibular scala, an intermediate channel called the middle scala and a lower channel called the scala tympani. The hair cells are connected to the spiral ganglion cells of the cochlear nerve 105 that resides in the modiolus. In response to received sounds transmitted by the middle ear 103, the fluid-filled cochlea 104 acts as a transducer to generate electrical pulses that are transmitted to the cochlear nerve 105 and ultimately to the brain.

[0005] Hearing is impaired when there is a problem with the ability of the neural matrix along the cochlea 104 to convert external sounds into meaningful action potentials. In order to improve impaired hearing, hearing prostheses have been developed. For example, when the damage is related to the operation of the middle ear 103, a conventional hearing aid or middle ear implant can be used to provide acoustic-mechanical stimulation to the auditory system in the form of amplified sound. Or when the damage is associated with the cochlea 104, a cochlear implant with an implanted stimulation electrode can electrically stimulate the auditory nerve tissue with a small current delivered by a plurality of electrode contacts distributed along the electrode.

[0006] Figure 1Also shown are some components of a typical cochlear implant system, including an external microphone that provides an audio signal input to an external signal processor 111, where various signal processing schemes may be implemented. The processed signal is then converted into a digital data format (such as a sequence of data frames) for transmission to an implant receiver 108 via an external transmitting coil 107. In addition to receiving the processed audio information, the implant receiver 108 performs additional signal processing, such as error correction, pulse forming, etc., and generates a stimulation pattern (based on the extracted audio information) that is sent to an implanted electrode array 110 via electrode leads 109. The electrode array 110 includes a plurality of electrode contacts 112 (also referred to as electrode channels) on its surface that provide selective stimulation of the cochlea 104.

[0007] A relatively small number of electrode channels are each associated with a relatively wide frequency band, with each electrode contact addressing a group of neurons with an electrical stimulation pulse having a charge derived from the instantaneous amplitude of the signal envelope within that frequency band. Current cochlear implant encoding strategies map different sound frequency channels to different locations within the cochlea. Figure 2 An example of processing signals using a cochlear implant stimulation (CIS) stimulation strategy is shown. Figure 2 The top portion of shows the sound pressure characteristics of "A" ( / ay / ) spoken at a sound level of 67.2 dB. Figure 2 The middle waveform in FIG. 1 shows the normal healthy auditory system response. Figure 2 The bottom waveform in shows the neural response of auditory nerve fibers under CIS stimulation.

[0008] Figure 3 The various functional blocks in the signal processing device for generating electrode stimulation signals to the electrode contacts in the implanted cochlear implant array according to a typical hearing implant system are shown. A pseudo code example of this arrangement can be set forth as:

[0009] Input signal processing:

[0010] BandPassFilter(input_sound,band_pass_signals)

[0011] Envelope Extraction:

[0012] BandPassEnvelope(band_pass_signals,band_pass_envelopes)

[0013] Stimulus timing generation:

[0014] TimingGenerate(band_pass_signals,stim_timing)

[0015] Pulse Generation:

[0016] PulseGenerate(band_pass_envelopes,stim_timing,out_pulses)

[0017] The details of this arrangement will be set forth in the discussion that follows.

[0018] exist Figure 3 In the signal processing device shown in FIG. 1 , the initial input sound signal is generated by one or more sensing microphones, which may be omnidirectional and / or directional. The preprocessor filter bank 301 preprocesses the input sound signal with a set of multiple parallel bandpass filters (each of which is associated with a specific frequency band of the audio) (e.g., infinite impulse response (IIR) filters or finite impulse response (FIR) filters), for example, using a filter bank with 12 6th-order infinite impulse response (IIR) type digital Butterworth bandpass filters, so that the acoustic audio signal is filtered into a number of K bandpass signals U1 to U K, where each signal corresponds to a frequency band in one of the bandpass filters. Each output of a sufficiently narrow CIS bandpass filter for a voiced speech input signal can be roughly regarded as a sine wave at the center frequency of the bandpass filter modulated by an envelope signal. This is also due to the quality factor (Q≈3) of the filter. In the case of a voiced speech segment, this envelope is approximately periodic, and the repetition rate is equal to the pitch frequency. Alternatively and non-limitingly, the preprocessor filter bank 301 can be implemented based on the use of a fast Fourier transform (FFT) or a short-time Fourier transform (STFT). Based on the acoustic organization of the cochlea, each electrode contact in the tympanic scale is typically associated with a specific bandpass filter of the preprocessor filter bank 301. The preprocessor filter bank 301 can also perform other initial signal processing functions, such as but not limited to automatic gain control (AGC) and / or noise reduction and / or wind noise reduction and / or beamforming and other well-known signal enhancement functions. A pseudocode example of an infinite impulse response filter bank based on a direct form II transposed structure is given by Fontaine et al.: Brian Hears: Online Auditory Processing Using Vectorization Over Channels, Frontiers in Neuroinformatics, 3011; the entire contents of which are incorporated herein by reference.

[0019] Bandpass signal U1 to U K (which can also be considered as an electrode channel) is output to the stimulation timer 306, which includes an envelope detector 302 and a fine structure detector 303. The envelope detector 302 extracts the characteristic envelope signal Y1, ..., Y representing the channel-specific bandpass envelope. K . Envelope extraction can be done by Y k =LP(|U k |) represents, where |.| represents the absolute value and LP(.) is a low-pass filter; for example, 12 rectifiers and 12 second-order IIR type digital Butterworth low-pass filters are used. Alternatively, if the bandpass signals U1,…,U K is generated by an orthogonal filter, the envelope detector 302 can extract the Hilbert envelope.

[0020] The fine structure detector 303 acts to obtain a smooth and robust estimate of the instantaneous frequency in the signal channel, thereby processing the bandpass signals U1, ..., U K The selected temporal fine structure features are used to increase the stimulation timing signal X1,…,XK The bandpass signal is U1, ..., U k can be assumed to be a real-valued signal, so in the specific case of an analytical orthogonal filter bank, the fine structure detector 303 only considers U k The fine structure detector 303 is composed of K independent, parallel submodules with the same structure.

[0021] The bandpass signal envelope Y1, ..., Y extracted from the envelope detector 302 K and the stimulation timing signals X1, ..., X1 from the fine structure detector 303 K The output from the stimulation timer 306 is to the pulse generator 304, which generates the electrode stimulation signal Z for the electrode contacts in the implanted electrode array 305. The pulse generator 304 applies a patient-specific mapping function adapted to the needs of the individual cochlear implant user during the fitting of the implant in order to achieve a natural loudness increase - for example, using a transient nonlinear compression of the envelope signal (mapping law). The pulse generator 304 can apply a logarithmic function with a shape factor C as the loudness mapping function, which is typically the same on all bandpass analysis channels. In different systems, different specific loudness mapping functions other than the logarithmic function may be used, where only one same function is applied to all channels or a separate function per channel to generate the electrode stimulation signal. The electrode stimulation signal is typically a symmetrical set of biphasic current pulses.

[0022] In order for an audio prosthesis such as a cochlear implant to work correctly, some patient-specific operating parameters need to be determined in a fitting adjustment procedure, where the type and number of operating parameters depends on the device and on the stimulation strategy. Possible patient-specific operating parameters of a cochlear implant include:

[0023] THR1 for electrode 1 (lower detection threshold for stimulus amplitude)

[0024] MCL1 (most comfortable loudness) for electrode 1

[0025] Phase duration of electrode 1

[0026] THR2 of electrode 2

[0027] MCL2 for electrode 2

[0028] Phase duration of electrode 2

[0029] ·……

[0030] Pulse rate

[0031] Number of fine structure channels

[0032] ·compression

[0033] Frequency parameters->Electrode mapping

[0034] Parameters describing the electric field distribution

[0035] These patient-specific operating parameters are saved in files called fitting maps. A given system may have multiple patient-specific fitting maps for different listening environments; for example, there may be one fitting map for a quiet environment and a different fitting map for a noisy environment. The better the fitting map, the more closely the hearing experience from the electrical stimulation signals resembles the natural hearing experience of an unimpaired individual.

[0036] A common approach to fit tuning is to behaviorally find the threshold (THR) and most comfortable loudness (MCL) values ​​for each individual electrode contact. See, e.g., Fitting Guide for First Fitting with MAESTRO 2.0, MED-EL, Fürstenweg 77a, 6020 Innsbruck, 1.0 Edition, 2007. AW 5420 Rev. 1.0 (English_EU), which is incorporated herein by reference. Other alternatives / extensions are sometimes used with simplified sets of operating parameters, for example, as proposed by Smoorenburg, Cochlear Implant Ear Marks, University Medical Centre Utrecht, 2006 and U.S. Patent Application 20060235332, which are incorporated herein by reference. Typically, each stimulation channel is fitted separately without using information from already fitted channels. The stimulation current on a given electrode is usually increased in a step-wise manner from zero until the MCL or THR is reached.

[0037] One method for objective measurement of MCL and THR is based on the measurement of ECAP (Electrically Evoked Compound Action Potential), as described by Gantz et al., Intraoperative Measures of Electrically Evoked Auditory Nerve Compound Action Potentials, American Journal of Otology 15(2):137-144 (1994), which is incorporated herein by reference. In this method, a recording electrode in the scala tympani of the inner ear is used. The overall response of the auditory nerve to electrical stimulation is measured at a location very close to the nerve excitation. This neural response is caused by the supra-position of a single neural response at the outside of the axonal membrane. The amplitude of the ECAP at the measurement location is typically in the μV range. When performing objective measurements (such as ECAP measurements) in existing cochlear implant systems, each electrode contact of the implantable electrode array is typically scanned separately, thereby increasing the stimulation signal current on the electrode contact in a stepwise manner from zero or a very low level until an ECAP response is detected. Other objective measures are also known, such as the electrically evokedstapedius reflex threshold (eSRT).

[0038] Once the fitting parameters (such as MCL and THR) are initially established based on objective measurements, the audiologist can further fine-tune the fitting graph based on their experience and any available subjective feedback from individual patients to modify the existing fitting graph by scaling, tilting, smoothing, or changing the shape of the fitting graph. However, the audiologist performing the fitting needs to have many years of clinical experience, and the fitting process can be quite time-consuming. Even testing some of the many possible adjustment combinations is not trivial. In addition, patient feedback is not always available; for example, when the patient is a child.

[0039] Some attempts have been made to make fitting faster or more automated. The latest development in this area is the fitting based on auditory response telemetry of Med-El's MAESTRO 7.0.1, called "ARTFit", which aims to fit based on objective measurements. During these objective measurements, the volume is increased from low to high until an objective response is measured. Ideally, this process is performed on each electrode until a response is found or until the subject feels the need to indicate that the stimulation has become too uncomfortable. Essentially, this means that although an objective response is measured, the subject still needs to be able to indicate that the stimulation has become too loud in order to obtain that objective response.

[0040] Despite the fact that measurements can be made on sedated patients or patients under general anesthesia, it is still uncommon to routinely make objective measurements during implant surgery due to time constraints. Current fitting strategies require adjustment of individual channels and then adjustment of the overall loudness. This process needs to be completed in full in order to obtain a reliable graph. Some efforts have been made to replace part of the process with objective measurements. These require relatively long measurements, which themselves require loudness judgments to work. Once the objective measurements are completed, they produce a graph distribution, which then again needs to be adjusted in real time. Summary of the invention

[0041] Embodiments of the present invention relate to a fitting arrangement for fitting electrode contacts of a cochlear implant electrode array implanted in a cochlea of ​​an implanted patient. This includes: iteratively fitting a plurality of fitting electrode contacts by performing the following for each of the fitting electrode contacts: i. delivering a fitting stimulation signal to the fitting electrode contact and at least one adjacent electrode contact to stimulate adjacent auditory nerve tissue, wherein the fitting stimulation signal is characterized by a charge level distribution function having a non-zero noise level charge at at least one adjacent electrode contact and a response level charge that is much greater than the noise level charge at the fitting electrode contact; and ii. obtaining a patient response to the fitting stimulation signal from the implanted patient. Then, based on the patient response, a patient-specific fitting map is defined for the electrode contacts of the cochlear implant electrode array.

[0042] In other specific embodiments, the charge level distribution function can be a Gaussian function or a geometric distribution function with a peak value corresponding to the response level charge. The fitted electrode contacts can be sequentially fitted starting from the top of the electrode array and backward along the length of the electrode array. Or the fitted electrode contacts can be fitted in a nonlinear order along the electrode array and / or in an alternating order of every other electrode contact along the length of the electrode array. The patient response can include subjective and / or objective response measurements.

[0043] Embodiments of the present invention also include a cochlear implant system that is fitted to an implanted patient using any of the above methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 The anatomy of a typical human ear with a cochlear implant system is shown.

[0045] Figure 2 An example of signal processing using a cochlear implant stimulation (CIS) stimulation strategy is shown.

[0046] Figure 3 Various functional blocks in the signal processing arrangement of a typical cochlear implant system are shown.

[0047] Figure 4 A block diagram of a cochlear implant fitting system according to an embodiment of the present invention is shown.

[0048] Figure 5 Various logical steps in a fitting process according to an embodiment of the present invention are shown.

[0049] FIG. 6A to FIG. 6C The charge distribution of the fitting process according to one specific embodiment is shown.

[0050] 7A to 7C The charge distribution of the fitting process according to another specific embodiment is shown. DETAILED DESCRIPTION

[0051] Embodiments of the present invention are directed to a cochlear implant fitting arrangement that generates a patient-specific fitting map more quickly than using existing methods without undesirably increasing the risk of overstimulation (without exceeding the MCL). The described method applies stimulation to the cochlear implant recipient in the most comfortable manner by masking adjacent electrodes. The method also applies charge levels to multiple electrode contacts to provide a more time-efficient fitting process.

[0052] Figure 4 A block diagram of a cochlear implant fitting system according to an embodiment of the present invention is shown. A control unit 401 for recording and stimulation (e.g., a Med-El Maestro Cochlear Implant (CI) system) generates stimulation signals and analyzes response measurements. Connected to the control unit 401 is an interface box 402, such as a diagnostic interface system, such as the DIB II conventionally used with the Maestro CI system, which formats and distributes input and output signals between the control unit 401 and the system components implanted in the patient 406. For example, Figure 4 As shown, there may be an interface lead 403 connected to an interface box 402 at one end and having an electrode plug 407 at the other end, which then separates into a cochlear implant electrode array 405 and an extra-cochlear ground electrode 404. A control unit 401 is configured to fit the electrode contacts of the cochlear implant electrode array 405. The control unit 401 includes a fitting processor of a processor device having at least one implant hardware, and is controlled by software instructions to perform a fitting process, including delivering a test stimulation sequence to at least one of the electrode contacts, the test stimulation sequence being at a variable charge level and a variable stimulation rate over time. After delivering the stimulation pulses, the electrode contacts on the cochlear implant electrode array 405 can be used as sensing elements to determine the current and voltage characteristics of the adjacent tissue.

[0053] More specifically, the operation Figure 4 The fitting system depicted in Figure 5The basic logical steps shown are to iteratively fit multiple fitting electrode contacts on the implanted electrode array. First, step 501, select a set of fitting contacts. For example, this can be all electrode contacts starting from the top of the electrode array and sequentially backward along the length of the electrode array. Or the selected set of fitting electrode contacts can be all electrode contacts fitted in a nonlinear order along the electrode array. Or the selected set of fitting contacts can be an alternating sequence of every other electrode contact along the length of the electrode array. The latter case reduces the required time by 50%. The fitting parameters of the unselected electrode contacts can be calculated by interpolating (or extrapolating) from the parameters derived for the selected electrode contacts.

[0054] Then, for each of the fitting electrode contacts, step 502, a fitting stimulation signal is delivered to the fitting electrode contact and at least one adjacent electrode contact to stimulate adjacent auditory nerve tissue (step 503). The fitting stimulation signal is characterized by a charge level distribution function having a non-zero noise level charge at at least one adjacent electrode contact and a response level charge that is much greater than the noise level charge at the fitting electrode contact. For a distribution function with a peak value k and a parameter p, and a noise function with random values ​​from 0 to q:

[0055] chargeLvl(x,n)=chargeLvl(x,n-1)+dist(k,p)+noise(x,q)

[0056] chargeLvl(x,0)=constant

[0057] noise(k,q)=0.

[0058] Then, the patient's response to the fitting stimulation signal is obtained from the implanted patient (which response may include subjective and / or objective response measures), step 504. This is done for each fitting electrode contact, while saving the charge level of each individual electrode contact providing the stimulation signal. Based on the patient's response, a patient-specific fitting map is defined for the electrode contacts of the cochlear implant electrode array, step 505.

[0059] FIG. 6A to FIG. 6C The charge distributions for three iterations of the fitting process are shown, where the charge level distribution function is a Gaussian distribution function with a peak corresponding to the response level charge. For example, a particular Gaussian distribution function may have standard derivatives σ=0,5 and μ=1. 7A to 7C The charge distributions for three iterations of the fitting process are shown, where the charge level distribution function is a geometric distribution function with a peak corresponding to the response level charge, p=0.9, p∈(0,1) and k=1, where the values ​​of μ and k represent the electrode contact currently being fitted.

[0060] These techniques are particularly useful for electrode arrays with a small number of electrode contacts because the number of iterations required is equal to the number of electrode contacts. It should be understood that the charge level on all electrode contacts rises steadily with the number of iterations. This means that the initial charge level of the response measurement is high, but the desired maximum charge level can still be calculated faster because the charge level should not be too high. Alternatively, a relative factor between the selected fitting electrode contact and at least one adjacent electrode contact can be selected to avoid at least one adjacent electrode contact being too loud. Alternatively, this risk can be avoided by setting a maximum charge level limit on all electrode contacts, and the charge level on the adjacent electrode contact cannot exceed the maximum charge level limit.

[0061] The fitting process typically starts with a flat graph at the MCL level. A clinical randomization factor may be selected based on the patient's ability to judge loudness. The patient may then be presented with different versions of the random graph with instructions for judging whether the graph is "too loud." Each of the graphs may be presented for 5 seconds unless the user presses the "too loud" / "skip" button. The longer the fitting process runs, the better the final graph, and the final graph is based on the maximum charge level measured for each electrode contact.

[0062] Background stimulation on adjacent electrode contacts makes loudness more tolerable to the patient, especially for electrode contacts close to the electrode opening into the cochlea, where high frequency sounds are perceived. Higher starting values ​​are selected for each consecutive electrode contact based on previous iterations of stimulation, which results in a more time-efficient fitting process. There is also a better simulation of channel interactions during fitting of each individual electrode contact, so the channel interaction part of the fitting process can be omitted.

[0063] Embodiments of the present invention may be implemented in part in any conventional computer programming language. For example, preferred embodiments may be implemented in a procedural programming language (e.g., "C") or an object-oriented programming language (e.g., "C++", Python). Alternative embodiments of the present invention may be implemented as pre-programmed hardware elements, other related components, or a combination of hardware and software components.

[0064] Embodiments may be implemented in part as a computer program product for use with a computer system. Such implementations may include a series of computer instructions that are either fixed on a tangible medium (such as a computer-readable medium (e.g., a disk, CD-ROM, ROM, or fixed disk)) or may be transmitted to a computer system via a modem or other interface device (such as a communication adapter connected to a network via a medium). The medium may be a tangible medium (e.g., an optical communication line or an analog communication line) or a medium implemented using wireless technology (e.g., microwave, infrared, or other transmission technology). The series of computer instructions implements all or part of the functions previously described herein for the system. Those skilled in the art will appreciate that such computer instructions may be written in a variety of programming languages ​​for use with many computer architectures or operating systems. In addition, such instructions may be stored in any memory device, such as a semiconductor, magnetic, optical, or other memory device, and may be transmitted using any communication technology, such as optical transmission technology, infrared transmission technology, microwave transmission technology, or other transmission technology. It is contemplated that such a computer program product may be distributed as a removable medium with accompanying printed or electronic documentation (e.g., a shrink-wrapped software package), preloaded with a computer system (e.g., on a system ROM or fixed disk), or distributed from a server or electronic bulletin board over a network (e.g., the Internet or the World Wide Web). Of course, some embodiments of the present invention may be implemented as a combination of both software (e.g., a computer program product) and hardware. Other embodiments of the present invention are implemented as either entirely hardware or entirely software (e.g., a computer program product).

[0065] Although various exemplary embodiments of the present invention have been disclosed, it will be apparent to those skilled in the art that various changes and modifications can be made which will achieve some of the advantages of the present invention without departing from the true scope of the invention.

Claims

1. A non-transitory tangible computer readable medium having instructions thereon for fitting a hearing implant system implanted in a patient and having an implant electrode array with a plurality of electrode contacts, the instructions comprising: Iteratively fit multiple fitted electrode contacts by doing the following for each of the fitted electrode contacts: i. delivering a fitting stimulation signal to the fitting electrode contact and at least one adjacent electrode contact to stimulate adjacent auditory nerve tissue, wherein the fitting stimulation signal in a single iteration of the fitting signal is characterized by a charge level distribution function having a non-zero noise level charge at the at least one adjacent electrode contact and a response level charge that is much greater than the noise level charge at the fitting electrode contact; as well as ii. obtaining a patient response to the fitting stimulation signal from the implanted patient; as well as Based on the patient responses, a patient-specific fit map is defined for electrode contacts of a cochlear implant electrode array.

2. The computer-readable medium of claim 1, wherein: The charge level distribution function is a Gaussian distribution function having a peak value corresponding to the response level charge.

3. The computer-readable medium of claim 1, wherein: The charge level distribution function is a geometric distribution function having a peak value corresponding to the response level charge.

4. The computer-readable medium of claim 1, wherein: The fitting electrode contacts are fitted sequentially along the length of the electrode array starting from the top end of the electrode array and working backwards.

5. The computer-readable medium of claim 1, wherein: The fitted electrode contacts are fitted in a non-linear order along the electrode array.

6. The computer-readable medium of claim 1, wherein: The fitted electrode contacts are fitted in an alternating order of every other electrode contact along the length of the electrode array.

7. The computer-readable medium of claim 1, wherein: The patient response includes a subjective response measure.

8. The computer-readable medium of claim 1, wherein: The patient response includes an objective response measure.

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