System and method for detection of disturbed basilar membrane wave propagation

Abstract

The present invention relates to systems and methods for detecting disturbed basilar membrane wave propagation and systems for monitoring electrode insertion into a patient with residual hearing. The Electrocochleography (ECochG) signal is measured on a subset of electrode contacts located in the inner are of a patient. The two electrode contacts with peak amplitude of the measured Electrocochleography (ECochG) signals are selected. For the two selected electrode contacts the phase-shift from the associated measured Electrocochleography (ECochG) signals is determined. If the phase-shift between the two electrode contacts differ by more than a predetermined threshold, a disturbed basilar membrane wave propagation in the area from the selected first electrode contact to the selected second electrode contact is detected.

Description

[0001] System and method for detection of disturbed basilar membrane wave propagation

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to systems and methods for detecting disturbed basilar membrane wave propagation and systems for monitoring electrode insertion into a patient with residual hearing.

[0004] BACKGROUND OF THE INVENTION

[0005] A normal ear transmits sounds as shown in FIG. 1 through the outer ear 101 to the tympanic membrane 102 which moves the bones of the middle ear 103 (malleus, incus, and stapes) that vibrate the oval window and round window membrane openings of the cochlea 104. The cochlea 104 is a long narrow cavity spirally wound about its axis for approximately two and a half turns in a human cochlea. It includes an upper channel known as the scala vestibuli and a lower channel known as the scala tympani separated with the cochlea duct known as scala media and connected by the helicotrema. The scala tympani is separated along the cochlea 104 by the basilar membrane from the scala media. The basilar membrane is a main structural element and determines the mechanical wave propagation properties of the cochlear partition. The axial center of the cochlea 104 is called the modiolus where the spiral ganglion cells of the auditory nerve 113 reside. In response to received sounds transmitted by the middle ear 103, the fluid-filled cochlea 104 functions as a transducer to generate electric pulses which are sensed by the acoustic nerve 113 and sent to the brain.

[0006] In some patients with some residual hearing in the lower acoustic frequencies, a conventional hearing aid and a cochlear implant can be combined together in a hybrid Electric Acoustic Stimulation (EAS) system. The term EAS as used herein is not limited to combined electric and acoustic stimulation only but includes combined electric and mechanic or vibratory stimulation. The hearing aid acoustically amplifies lower acoustic frequencies perceived by human ear, while the cochlear implant electrically stimulates the middle and high frequencies. See von Ilberg et al, Electric - Acoustic Stimulation of the Auditory System , ORL 61:334-340; Skarzynski et al, Preservation of Low Frequency Hearing in Partial Deafness Cochlear Implantation ( PDCI ) Using the Round Window Surgical Approach , Acta OtoLaryngol 2007; 127:41-48; Gantz & Turner, Combining Acoustic and Electrical Speech Processing: lowa / Nucleus Hybrid Implant , Acta Otolaryngol 2004; 124:344-347; Gstottner et al., Hearing Preservation in Cochlear Implantation for Electric Acoustic Stimulation , Acta Otolaryngol 2004; 124:348-352; all incorporated herein by reference. FIG. 1 also shows some components of a typical EAS system which includes an external microphone that provides an acoustic signal input to an external signal processor in where two different signal processing paths are developed. An upper acoustic frequency range communications signal containing middle and high frequency range acoustic is converted into a digital data format, such as a sequence of data frames, for transmission via a transmitter coil 107 over a corresponding implanted receiver coil 106 into the electric implant 108. Besides receiving the processed acoustic information, the electric implant 108 also performs additional signal processing such as error correction, pulse formation, etc., and produces an electric stimulation pattern (based on the extracted acoustic information) that is sent through an electrode lead 109 to an implanted electrode array 110 in the scala tympani. The electrode array 110 includes multiple electrode contacts along its length on its outer surface that provide selective electric stimulation of the cochlea 104. The electrode contacts are typically numbered in ascending order starting from the tip to the rear end of the electrode assembly adjacent the electrode lead 109 or vice versa. The external signal processor 111 also creates a lower acoustic frequency range communications signal to a conventional hearing aid 105 in the ear canal which acoustically stimulates the tympanic membrane 102, and in turn the middle ear 103 and cochlea 104. The invention however is not limited to an EAS system as described above. For example, the EAS system may provide the acoustic stimulation in various ways to the cochlea 104. For example with an implanted transducer attached to an ossicle in the middle ear 103 or via bone conduction with implanted or non-implanted active or passive transducers.

[0007] To achieve optimal hearing preservation outcomes in a large population of EAS patients, a controlled electrode array insertion is typically used to prevent trauma to the patient cochlear. In order to improve the electrode array insertion, many attempts have been made to provide the surgeon real-time feedback. This may allow the surgeon to take manual corrections and prevent trauma. Such a system is disclosed in US9107621B2 an earlier patent from the current inventor. Not only preventing trauma during electrode array insertion is important to the hearing outcome of EAS patients, also undisturbed cochlear mechanics for the acoustic stimulation. US8630721B2 discloses an electrode array that shall preserve cochlear mechanics, but very thin electrodes have other issues, such as kinking and their effectiveness is not sufficiently proofed. Instead of an slim electrode design, the inventors have found that the location of the electrode array 110 within the scala tympani is most significant to preserving cochlear mechanics and thus hearing outcome for EAS patients. In case the electrode array touches the basilar membrane, this typically causes a disturbance of the cochlear mechanics due to the disturbance of the basilar membrane (traveling) wave propagation. The cochlear mechanics also changes, in case the electrode array 110 touches areas within the scala tympani where the basilar membrane is suspended for the same reason. In the following and throughout this description, the term disturbed basilar membrane wave propagation refers to all causes due to the electrode array no touching areas within the scala tympani that affect the basilar membrane (traveling) wave propagation, i.e. affect cochlear mechanics. Therefore, a need exists to determine if and at which location within the scala tympani the electrode array no disturbs the basilar membrane wave propagation.

[0008] SUMMARY OF THE INVENTION

[0009] The present invention aims at overcoming the aforementioned disadvantages of the prior art with a method according to claim i and a system for detecting a disturbed basilar membrane wave propagation according to claim io and a system for monitoring the insertion of an electrode array into an inner ear of a patient claim 21. Preferred embodiments of the invention are defined in the dependent claims.

[0010] The method for detecting a disturbed basilar membrane wave propagation according one aspect of the invention comprises the steps of in a first step measuring for at least a subset of electrode contacts of an electrode array located in the inner ear of a patient a Electrocochleography (ECochG) signal when an acoustic signal of a predetermined frequency is applied to the outer ear of the patient. In a second step selecting a first electrode contact and a second electrode contact based at least in part on a peak amplitude of the measured Electrocochleography (ECochG) signals or alternatively selecting a first electrode contact and a second electrode contact is based at least in part on adjacent peak amplitudes of the measured Electrocochleography (ECochG) signals. In a third step determining a first phaseshift for the selected first electrode contact and a second phase-shift for the selected second electrode contact from the associated measured Electrocochleography (ECochG) signal. And in a fourth step determining that a disturbed basilar membrane wave propagation in the area from the selected first electrode contact to the selected second electrode contact exists based at least in part when the first phase-shift and second phase-shift differ by more than a predetermined threshold.

[0011] In the method in accordance with the invention the predetermined threshold may include a phase-shift between the first electrode contact and second electrode contact when no disturbed basilar membrane wave propagation is present and / or the predetermined threshold may at least be 90 degrees or at least be 180 degrees.

[0012] The inventive method in one aspect may use for the predetermined frequency of the acoustic signal is 500Hz, 1000Hz or 2000Hz. The predetermined frequency of the acoustic signal may be a function of the insertion location of the electrode array in the inner ear of the patient. The function may determine the predetermined frequency based on the tonotopic location of the electrode array tip. The predetermined frequency of the acoustic signal may be selected to be lower than or at the tonotopic location of the estimated area where the wave propagation of the basilar membrane is disturbed and the estimated area where the wave propagation of the basilar membrane is disturbed is first derived with the inventive method as disclosed herein.

[0013] The amplitude of the acoustic signal may be at least qodB above the audiological threshold.

[0014] The system for detecting a disturbed basilar membrane wave propagation in accordance with one aspect of the present invention comprises a measurement unit for measurement of the Electrocochleography (ECochG) signal of an electrode contact of an electrode array located in the inner ear of a patient and a control unit. The control unit is adapted for carrying out the step of measuring with the measurement unit for at least a subset of electrode contacts of an electrode array located in the inner ear of a patient a Electrocochleography (ECochG) signal when an acoustic signal of a predetermined frequency is applied to the outer ear of the patient. The control unit is further adapted to then select a first electrode contact and a second electrode contact based at least in part on a peak amplitude of the measured Electrocochleography (ECochG) signals. The control unit is further adapted to then determine the first phase-shift for the selected first electrode contact and a second phaseshift for the selected second electrode contact from the associated measured Electrocochleography (ECochG) signal. The control unit is further adapted to determine that a disturbed basilar membrane wave propagation in the area from the selected first electrode contact to the selected second electrode contact exists based at least in part when the first phase-shift and second phase-shift differ by more than a predetermined threshold. The control unit is further adapted for providing a signal representative of the determined disturbed basilar membrane wave propagation.

[0015] In a further aspect, the control unit may be adapted to apply a predetermined threshold which includes a phase-shift between the first electrode contact and second electrode contact when no disturbed basilar membrane wave propagation is present. The system may include a memoiy for storing averaged phase-shifts between electrode contacts representing phaseshifts when no disturbed basilar membrane wave propagation is present. Alternatively, the predetermined threshold maybe at least 90 degrees or at least 180 degrees.

[0016] The system may further comprise a transducer adapted for placement close to the outer ear of the patient and operatively coupled to the control unit and the control unit further adapted to provide a control signal to the transducer, such that the transducer emits an acoustic signal. The acoustic signal may have a certain frequency, which may be 500Hz, 1000Hz, or 2000Hz. The control unit may be further adapted for determining a control signal for the transducer based at least in part on the signal representative of the determined disturbed basilar membrane wave propagation or alternatively may include the tonotopic location associated with the disturbed basilar membrane wave propagation.

[0017] The system may further comprise an insertion detection unit adapted for providing an insertion location information of the electrode array in the patient inner ear and the control unit is further adapted to estimate the tonotopic location based on the electrode array insertion location information. In a further aspect, the system may further comprise an output unit for providing to a user the signal representative of the determined disturbed basilar membrane wave propagation so as to indicate disturbed basilar membrane wave propagation and / or indicate the area of disturbed basilar membrane wave propagation.

[0018] The system for monitoring the insertion of an electrode array into an inner ear of a patient in accordance with one aspect of the invention, comprises an output unit, an insertion detection unit adapted for providing an insertion location information of the electrode array in the patient inner ear, a measurement unit for measurement of the Electrocochleography (ECochG) signal of an electrode contact of an electrode array located in the inner ear of a patient and a control unit adapted for carrying out the step of measuring with the measurement unit for at least a subset of electrode contacts of an electrode array located in the inner ear of a patient a Electrocochleography (ECochG) signal when an acoustic signal of a predetermined frequency is applied to the outer ear of the patient. The control unit is further adapted to carry out the step of selecting a first electrode contact and a second electrode contact based at least in part on a peak amplitude of the measured Electrocochleography (ECochG) signals. The control unit is further adapted to carry out the step of determining a first phase-shift for the selected first electrode contact and a second phase-shift for the selected second electrode contact from the associated measured Electrocochleography (ECochG) signal. The control unit is further adapted to carry out the step of determining that a disturbed basilar membrane wave propagation in the area from the selected first electrode contact to the selected second electrode contact exists based at least in part when the first phase-shift and second phase-shift differ by more than a predetermined threshold. The control unit is further adapted to carry out the step of providing on the output unit a signal representative of the determined disturbed basilar membrane wave propagation.

[0019] The control unit may be further adapted to estimate the tonotopic location associated with the disturbed basilar membrane wave propagation based on the electrode array insertion location information and providing on the output unit the tonotopic location information.

[0020] The system may further comprise a transducer adapted for placement close to the outer ear of the patient and operatively coupled to the control unit and the control unit further adapted to provide a control signal to the transducer, such that the transducer emits an acoustic signal. The control unit may be further adapted for determining a control signal for the transducer based at least in part on the signal representative of the determined disturbed basilar membrane wave propagation or alternatively based at least in part on the signal representative of the determined disturbed basilar membrane wave propagation includes the tonotopic location associated with the disturbed basilar membrane wave propagation.

[0021] The system may further include a user input unit through which the user can adapt at least in part the predetermined threshold. The control unit may be adapted to apply a predetermined threshold that includes a phase-shift between the first electrode contact and second electrode contact when no disturbed basilar membrane wave propagation is present.

[0022] BRIEF DESCRIPTION OF THE FIGURES

[0023] Embodiments of the present invention are described herein in conjunction with the accompanying drawings, in which:

[0024] Fig. 1 (prior art) shows a typical human ear having an acoustic electric hearing implant system.

[0025] Fig. 2A-B shows the measured ECochG signal amplitude in (A) and the ECochG signal phase in (B) for each electrode contact where the wave propagation of the basilar membrane is not disturbed.

[0026] Fig. 3 shows a flow diagram schematically illustrating a method in accordance with embodiments of the invention.

[0027] Fig. 4A-B shows the measured ECochG signal amplitude in (A) and the ECochG signal phase in (B) for each electrode contact where the wave propagation of the basilar membrane is disturbed.

[0028] Fig. 5A-B shows the measured ECochG signal amplitude in (A) and the ECochG signal phase in (B) for each electrode contact where the wave propagation of the basilar membrane is disturbed.

[0029] Fig. 6A-B shows the measured ECochG signal amplitude in (A) and the ECochG signal phase in (B) for each electrode contact where the wave propagation of the basilar membrane is disturbed.

[0030] Fig. 7 is a schematic drawing of a system for monitoring the insertion of an electrode array into an inner ear of a patient according to embodiments of the invention.

[0031] DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION For the purposes of promoting an understanding of the principles of the invention, reference will now be made to examples illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated apparatus and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur now or in the future to one skilled in the art to which the invention relates.

[0032] Embodiments of the present invention provide useful information about disturbed basilar membrane wave propagation, which may be used for real time intraoperative feedback to the surgeon. This helps to evaluate surgical steps and guide the surgeon to minimize disturbed basilar membrane wave propagation during insertion of the cochlear implant electrode array into the inner ear of a patient. After detecting a disturbed basilar membrane wave propagation, the electrode array may be drawn back slightly by the surgeon, turned and then continue inserting the electrode array. Dependent on the area where a disturbed basilar membrane wave propagation is detected, the surgeon can apply a proper manual intervention, for example turning or re-traction of the electrode array, during insertion of the cochlear implant electrode array. The method for detecting disturbed basilar membrane wave propagation can be used any time during insertion of the electrode array or when the electrode array is fully inserted or even post-surgery for e.g. diagnosing purposes.

[0033] Fig. 2A shows the measured Electrocochleography (ECochG) signal for each measured electrode contact and Fig. 2B shows the phase-shift of the ECochG signal for each electrode contact where the wave propagation of the basilar membrane is not disturbed. Electrocochleography (or ECochG as used throughout this description) refers to a clinical measurement technique that can be used to, for example, assess a recipient’s residual hearing. ECochG involves the delivery of acoustic stimuli to a patients cochlea, e.g. with an transducer placed close to the patient’s outer ear, and measuring the electric signal, typically the voltage, on one or more electrode contacts of the electrode array. These responses are the ECochG signals and are shown in diagram on the right hand-side of Fig. 2A for each measured electrode contact (labelled with the electrode contact number on the y-axis) as a function of time (x-axis). The acoustic signal may have a predetermined frequency and may be delivered through the outer ear of the patient to the inner ear of the patient and an ECochG response / signal is measured at e.g. an electrode contact of the electrode array located in the patient’s inner ear. The acoustic signal is preferably a sinusoidal signal or one with a narrow bandwidth, but any acoustic signal can be used, as long as the signal evokes a traveling wave over at least that portion of the basilar membrane where the electrode array may touch the basilar membrane and may cause disturbed basilar membrane wave propagation. The predetermined frequency of the acoustic signal may for example be 500Hz, IOOOHZ or 2000Hz or may be a function of the insertion location of the electrode array in the inner ear of the patient, which may be based on the tonotopic location of the electrode array tip. On the upper left hand-side of Fig. 2A the amplitude of the ECochG-signal on the y-axis for each measured electrode contact on the x-axis is shown. The term peak amplitude for an electrode contact refers to an ECochG signal amplitude of that electrode contact that is statistically significantly higher than the ECochG signal amplitude of the two measured immediate adjacent electrode contacts. On the lower left hand-side of Fig. 2A the latency of the basilar membrane traveling wave is shown. Fig. 2B shows the phase shift on the y-axis for each measured electrode contact (on the x-axis) in relation to a (time) reference. The reference may be the acoustic signal or the measured ECochG-signal for one selected electrode contact. In Fig. 2B electrode contact number 12 is the reference, hence phase-shift for this electrode is zero.

[0034] Fig. 3 shows a flowchart of one exemplary embodiment according to the present invention for detecting a disturbed basilar membrane wave propagation. At step 301 a Electrocochleography (ECochG) signal when an acoustic signal of a predetermined frequency is applied to the outer ear of the patient for a subset of electrode contacts of an electrode array located in the inner ear of a patient is measured. The electrode array includes multiple electrode contacts along its length on its outer surface that provide selective electric stimulation or allow for selective measurement of the Electrocochleography (ECochG) signal within the cochlea. The electrode contacts are numbered in ascending order starting from the tip to the rear end of the electrode assembly adjacent the electrode lead or vice versa. For example, electrode contact numbered E5 is adjacent to electrode contact numbered E4 and electrode contact numbered E3. The acoustic signal may have a predetermined frequency and may be delivered to the inner ear with a transducer through the outer ear of the patient to the inner ear of the patient. Without departing from the inventive concept, it is understood that the acoustic signal may be delivered to the inner ear from a transducer located at various other locations, e.g. close to or fixated to one of the ossicle bones or close to the oval or round window. Other ways to deliver the acoustic signal to the inner ear include bone-conduction. In this example the transducer is placed on the patient’s head.

[0035] The acoustic signal is preferably a sinusoidal signal or one with a narrow bandwidth, but any acoustic signal can be used, as long as the signal evokes a traveling wave over at least that portion of the basilar membrane where the electrode array may touch the basilar membrane and may cause disturbed basilar membrane wave propagation. The amplitude of the acoustic signal may be qodB above the audiological threshold. The predetermined frequency of the acoustic signal may for example be 500Hz, 1000Hz or 2000Hz or may be a function of the insertion location of the electrode array in the inner ear of the patient, which may be based on the tonotopic location of the electrode array tip. The predetermined frequency of the acoustic signal may also be selected to be lower than or at the tonotopic location of the estimated area where the wave propagation of the basilar membrane may be disturbed. This may be achieved by first determining the area where the wave propagation of the basilar membrane may be disturbed in accordance with the inventive method described herein and once that area is detected, using a frequency for the acoustic signal that corresponds to the tonotopic location where the area of the estimated disturbed wave propagation of the basilar membrane is located. Using such an acoustic signal improves the sensitivity of the measurement and even very small disturbances can be detected subsequently.

[0036] At step 302 a first electrode contact and a second electrode contact is selected based at least in part on a peak amplitude of the measured Electrocochleography (ECochG) signals. The term peak amplitude for an electrode contact refers to an ECochG signal amplitude of that electrode contact that is statistically significantly higher than the ECochG signal amplitude of the two measured immediate adjacent electrode contacts. Examples of peak amplitudes with reference to Fig. 4A are electrode contacts numbered E2, E5, E7 and E10 and with reference to Fig. 6A are the electrode contacts numbered E2, E5 and E10. At step 303 a first phase-shift for the selected first electrode contact and a second phase-shift for the selected second electrode contact from the associated measured Electrocochleography (ECochG) signal is determined. Examples of determined phase-shifts for each measured electrode contact are shown in Figs. 4B, 5B and 6B. The phase-shifts are in radians and negative values indicate that the ECochG-signal for the respective electrode contact is shifted to the left in the right- hand-side diagram of Fig. 2A compared to the reference. In the time-domain of the ECochG- signal this corresponds to the signal being timely ahead of the reference.

[0037] At step 304 it is determined if a disturbed basilar membrane wave propagation in the area from the selected first electrode contact to the selected second electrode contact exists based at least in part when the first phase-shift and second phase-shift differ by more than a predetermined threshold. The predetermined threshold may include a phase-shift between the first electrode contact and second electrode contact when no disturbed basilar membrane wave propagation is present. This has the advantage, that for the threshold natural occurring phase-shifts when no disturbed basilar membrane wave propagation takes place is taken into account and consequently the threshold can be set better and detection may be improved. In another example, the predetermined threshold may be at least 90 degrees or at least 180 degrees and may or may not include a phase-shift between the first electrode contact and second electrode contact when no disturbed basilar membrane wave propagation is present.

[0038] If at step 304 an area with disturbed basilar membrane wave propagation is detected, at step 305 a signal representative of the determined disturbed basilar membrane wave propagation is provided, for example and without limitation to an output unit 705 which may include a display and / or a buzzer. For example, during insertion of the electrode array, the surgeon can hear an alert signal through the buzzer and can keep his attention to the electrode array insertion area. At step 306 the method in accordance with the invention may detect another area where the basilar membrane wave propagation is disturbed, in case further ECochG peak amplitudes are present. It should be noted that this step is optional. In a similar manner and optional, the steps starting with step 301 can be repeated continuously, such that a realtime detection during e.g. insertion of an electrode array into the inner ear of the patient can be achieved.

[0039] Figs. 4A-B, 5A-B and 6A-B show examples of in-vivo measurements. All the measurements were taken for a fully inserted electrode array and an acoustic signal frequency of 500Hz was used. ECochG was measured on all electrodes (except electrode contact numbered 4, which was deactivated). In Fig. 4A in the diagram on the right hand-side, the ECochG-signal for all the measured electrode contacts as a function of time is shown. The left hand-side diagram shows the ECochG amplitudes for each measured electrode contact. This depiction is the exact same as used in Fig. 2A and is also used in the same way in Figs.sA and 6A. Fig. 4B shows the phase-shift of the ECochG signal for each measured electrode contact. This depiction is the exact same as used in Fig. 2B and is also used in the same way in Figs.sB and 6B. From Fig. 4A in the left-hand-side diagram the peak amplitudes can be seen. These are electrode contacts numbered E2, E5, E7 and E10. From Fig. 4B the phase-shift for each measured electrode contact can be seen. Phase-shifts exceeding the predetermined threshold are at electrode contact number E2, E6 and E10. In Figs. 5A and 5B the measurements are taken from the same patient and after the surgeon has withdrawn the electrode array by 0.5mm. Electrode contacts numbered E2, E5, E7 and 10 still have peak amplitudes, but the phase-shift for electrode contact number E10 vanished. Finally in Figs. 6A and 6B the electrode array was re-inserted fully after 0.5mm withdrawal and ECochG re-measured. In this example, the electrode contacts numbered E2, E5 and E10 have peak amplitudes, but the peak amplitude at electrode contact E7 vanished. The re-insertion did not change phase-shift and therefore phase-shifts exceeding the predetermined threshold are only present for electrode contacts E2 and E5 after withdrawing the electrode array by 0.5mm and reinsertion.

[0040] Fig. 7 schematically shows an exemplary system for detecting a disturbed basilar membrane wave propagation or monitoring insertion of an electrode array into the inner ear of a patient adapted for detecting a disturbed basilar membrane wave propagation in accordance with the invention. In the following the system for detecting a disturbed basilar membrane wave propagation system will be described by way of example with reference to Fig. 7. The system for detecting a disturbed basilar membrane wave propagation comprises a measurement unit 704 for measurement of the Electrocochleography (ECochG) signal of an electrode contact of an electrode array located in the inner ear of a patient and a control unit 701. The control unit 701 is adapted for carrying out the steps of first measuring with the measurement unit 701 for at least a subset of electrode contacts of an electrode array located in the inner ear of a patient a Electrocochleography (ECochG) signal when an acoustic signal of a predetermined frequency is applied to the outer ear of the patient. The control unit 701 is further adapted to then select a first electrode contact and a second electrode contact based at least in part on a peak amplitude of the measured Electrocochleography (ECochG) signals. The control unit 701 is further adapted to then determine the first phase-shift for the selected first electrode contact and a second phase-shift for the selected second electrode contact from the associated measured Electrocochleography (ECochG) signal. In a next step, the control unit 701 is adapted to determine that a disturbed basilar membrane wave propagation in the area from the selected first electrode contact to the selected second electrode contact exists based at least in part when the first phase-shift and second phase-shift differ by more than a predetermined threshold. Finally, the control unit 701 is adapted for providing a signal representative of the determined disturbed basilar membrane wave propagation.

[0041] The control unit 701 is further adapted to apply a predetermined threshold which includes a phase-shift between the first electrode contact and second electrode contact when no disturbed basilar membrane wave propagation is present. For this purpose, control unit 701 my include a memory for storing averaged phase-shifts between electrode contacts representing phase-shifts when no disturbed basilar membrane wave propagation is present. The averaged phase-shifts may be averages from measurements taken from a large number of patients where the electrode array is fully inserted or where no electrode array is inserted at all and no disturbed basilar membrane wave propagation is present. The average phase-shifts may be stored as a parametric function, such as a polynomial or logarithmic fitted function. The parametric function may be adaptable to the patient. For example, actual ECochG measurements from the patient may be used to fine-tune the parameters of the function so as to adapt the parametric function to the individual patient. This may improve the detection. In an alternative or in addition, the predetermined threshold may be at least 90 degrees or at least 180 degrees.

[0042] Optionally the system for detecting a disturbed basilar membrane wave propagation further comprises an acoustic transducer adapted for placement close to the outer ear of the patient and operatively coupled to the control unit 701. The control unit 701 is further adapted to provide a control signal to the transducer, such that the transducer emits an acoustic signal. The acoustic signal may have a predetermined frequency and may be delivered to the inner ear from a transducer through the outer ear of the patient to the inner ear of the patient. Without departing from the inventive concept, it is understood that the acoustic signal may be delivered to the inner ear through a transducer located at various other locations, e.g. close to or fixated to one of the ossicle bones or close to the oval or round window. Other ways to deliver the acoustic signal to the inner ear include bone-conduction. In this example the transducer is placed on the patient’s head.

[0043] Control unit 701 may output a control signal such that the transducer generates an acoustic signal is a sinusoidal signal or one with a narrow bandwidth. It is however understood, that any acoustic signal can be used, as long as the signal evokes a traveling wave over at least that portion of the basilar membrane where the electrode array may touch the basilar membrane and may cause disturbed basilar membrane wave propagation. Control unit 701 may output a control signal such that the transducer generates amplitude of the acoustic signal may be 4odB above the audiological threshold. Control unit 701 may output a control signal such that the transducer generates an acoustic signal of predetermined frequency, for example 500Hz, 1000Hz or 2000Hz or the predetermined frequency may be a function of the insertion location of the electrode array in the inner ear of the patient, which may be based on the tonotopic location of the electrode array tip. Alternatively, or in addition the control unit 701 may select the predetermined frequency of the acoustic signal to be lower than or at the tonotopic location of the estimated area where the wave propagation of the basilar membrane may be disturbed. This may be achieved by first determining the area where the wave propagation of the basilar membrane may be disturbed in accordance with the inventive method described above with reference to Fig. 3 and once that area is detected, using a frequency for the acoustic signal that corresponds to the tonotopic location where the area of the estimated disturbed wave propagation of the basilar membrane is located. Using such an acoustic signal frequency improves the sensitivity of the measurement and even very small disturbances may be detected.

[0044] Optionally the system for detecting a disturbed basilar membrane wave propagation further comprises an output unit 705 for providing to a user the signal representative of the determined disturbed basilar membrane wave propagation so as to indicate disturbed basilar membrane wave propagation and / or indicate the area of disturbed basilar membrane wave propagation. It should be noted that other means outputting information to a user are equally suitable for use with the inventive concept. For example, a buzzer could provide a surgeon an acoustic alarm signal when a disturbed basilar membrane wave propagation is detected.

[0045] While the foregoing largely also applies to the system for monitoring the insertion of an electrode array in accordance with an aspect of the invention, in the following the system for monitoring the insertion of an electrode array will be described by way of example only with reference to Fig. 7. The system for monitoring the insertion of an electrode array into an inner ear of a patient comprises an output unit 705, an insertion detection unit 702 adapted for providing an insertion location information of the electrode array in the patient inner ear, a measurement unit 704 for measurement of the Electrocochleography (ECochG) signal of an electrode contact of an electrode array located in the inner ear of a patient and a control unit 701. The control unit 701 is adapted for carrying out the steps of measuring with the measurement unit 701 for at least a subset of electrode contacts of an electrode array located in the inner ear of a patient a Electrocochleography (ECochG) signal when an acoustic signal of a predetermined frequency is applied to the outer ear of the patient. The control unit 701 further adapted carrying out the step of selecting a first electrode contact and a second electrode contact based at least in part on a peak amplitude of the measured Electrocochleography (ECochG) signals. The control unit 701 is adapted to then determine the first phase-shift for the selected first electrode contact and a second phase-shift for the selected second electrode contact from the associated measured Electrocochleography (ECochG) signal. The control unit 701 is adapted in a next step to determine that a disturbed basilar membrane wave propagation in the area from the selected first electrode contact to the selected second electrode contact exists based at least in part when the first phase-shift and second phase-shift differ by more than a predetermined threshold. Finally, the control unit 701 is adapted for providing on the output unit 705 a signal representative of the determined disturbed basilar membrane wave propagation. The output unit 705 may include a display and / or a buzzer and / or a network-interface.

[0046] The control unit 701 may further be adapted to estimate the tonotopic location associated with the disturbed basilar membrane wave propagation based on the electrode array insertion location information and providing on the output unit 705 the tonotopic location information.

[0047] The system for monitoring the insertion of an electrode array into an inner ear of a patient further comprises an acoustic transducer adapted for placement close to the outer ear of the patient and operatively coupled to the control unit 701. The control unit 701 is further adapted to provide a control signal to the transducer, such that the transducer emits an acoustic signal. The acoustic signal may have a predetermined frequency and may be delivered to the inner ear from a transducer through the outer ear of the patient to the inner ear of the patient. Without departing from the inventive concept, it is understood that the acoustic signal may be delivered to the inner ear through a transducer located at various other locations, e.g. close to or fixated to one of the ossicle bones or close to the oval or round window. Other ways to deliver the acoustic signal to the inner ear include bone-conduction. In this example the transducer is placed on the patient’s head. Control unit 701 may output a control signal such that the transducer generates an acoustic signal is a sinusoidal signal or one with a narrow bandwidth. It is however understood, that any acoustic signal can be used, as long as the signal evokes a traveling wave over at least that portion of the basilar membrane where the electrode array may touch the basilar membrane and may cause disturbed basilar membrane wave propagation. Control unit 701 may output a control signal such that the transducer generates amplitude of the acoustic signal may be 4odB above the audiological threshold. Control unit 701 may output a control signal such that the transducer generates an acoustic signal of predetermined frequency, for example 500Hz, 1000Hz or 2000Hz or the predetermined frequency may be a function of the insertion location of the electrode array in the inner ear of the patient, which may be based on the tonotopic location of the electrode array tip. Alternatively, or in addition the control unit 701 may select the predetermined frequency of the acoustic signal to be lower than or at the tonotopic location of the estimated area where the wave propagation of the basilar membrane may be disturbed. This may be achieved by first determining the area where the wave propagation of the basilar membrane may be disturbed in accordance with the inventive method described above with reference to Fig. 3 and once that area is detected, using a frequency for the acoustic signal that corresponds to the tonotopic location where the area of the estimated disturbed wave propagation of the basilar membrane is located. Using such an acoustic signal frequency improves the sensitivity of the measurement and even very small disturbances may be detected.

[0048] The system may include an input unit (not shown) through which the user can adapt at least in part the predetermined threshold. The control unit 701 is further adapted to apply a predetermined threshold which includes a phase-shift between the first electrode contact and second electrode contact when no disturbed basilar membrane wave propagation is present. For this purpose, control unit 701 my include a memory for storing averaged phase-shifts between electrode contacts representing phase-shifts when no disturbed basilar membrane wave propagation is present. The averaged phase-shifts may be averages from measurements taken from a large number of patients where the electrode array is fully inserted or where no electrode array is inserted at all and no disturbed basilar membrane wave propagation is present. The average phase-shifts may be stored as a parametric function, such as a polynomial or logarithmic fitted function. The parametric function may be adaptable to the patient. For example, actual ECochG measurements from the patient may be used to finetune the parameters of the function so as to adapt the parametric function to the individual patient. This may improve the detection. In an alternative or in addition, the predetermined threshold may be at least 90 degrees or at least 180 degrees.

Claims

CLAIMS1. A method for detecting a disturbed basilar membrane wave propagation comprising the steps: measuring for at least a subset of electrode contacts of an electrode array located in the inner ear of a patient a Electrocochleography (ECochG) signal when an acoustic signal of a predetermined frequency is applied to the outer ear of the patient; and selecting a first electrode contact and a second electrode contact based at least in part on a peak amplitude of the measured Electrocochleography (ECochG) signals; and determining a first phase-shift for the selected first electrode contact and a second phase-shift for the selected second electrode contact from the associated measured Electrocochleography (ECochG) signal; and determining that a disturbed basilar membrane wave propagation in the area from the selected first electrode contact to the selected second electrode contact exists based at least in part when the first phase-shift and second phase-shift differ by more than a predetermined threshold.

2. A method for detecting a disturbed basilar membrane wave propagation according to claim 1, wherein the predetermined threshold includes a phase-shift between the first electrode contact and second electrode contact when no disturbed basilar membrane wave propagation is present.

3. A method for detecting a disturbed basilar membrane wave propagation according to claim 1 or 2, wherein the predetermined threshold is at least 90 degrees or at least 180 degrees.

4. A method for detecting a disturbed basilar membrane wave propagation according to any of the claims 1 to 3, wherein the predetermined frequency of the acoustic signal is 500Hz, 1000Hz or 2000Hz.

5. A method for detecting a disturbed basilar membrane wave propagation according to any of the claims 1 to 3, wherein the predetermined frequency of the acoustic signal is a function of the insertion location of the electrode array in the inner ear of the patient.

6. A method for detecting a disturbed basilar membrane wave propagation according to claim 6, wherein the function determines the predetermined frequency based on the tonotopic location of the electrode array tip.

7. A method for detecting a disturbed basilar membrane wave propagation according to any of the claims 1 to 3, wherein the predetermined frequency of the acoustic signal is selected to be lower than or at the tonotopic location of the estimated area is determined based on a method of any of claims 1 to 3 where the wave propagation of the basilar membrane is disturbed.

8. A method for detecting a disturbed basilar membrane wave propagation according to any of the preceding claims, wherein the amplitude of the acoustic signal is at least 4odB above the audiological threshold.

9. A method for detecting a disturbed basilar membrane wave propagation according to any of the preceding claims, wherein selecting a first electrode contact and a second electrode contact is based at least in part on adjacent peak amplitudes of the measured Electrocochleography (ECochG) signals.

10. A system for detecting a disturbed basilar membrane wave propagation, the system comprising a measurement unit for measurement of the Electrocochleography (ECochG) signal of an electrode contact of an electrode array located in the inner ear of a patient and a control unit adapted for carrying out the steps of measuring with the measurement unit for at least a subset of electrode contacts of an electrode array located in the inner ear of a patient a Electrocochleography (ECochG) signal when an acoustic signal of a predetermined frequency is applied to the outer ear of the patient; selecting a first electrode contact and a second electrode contact based at least in part on a peak amplitude of the measured Electrocochleography (ECochG) signals; and determining a first phase-shift for the selected first electrode contact and a second phase-shift for the selected second electrode contact from the associated measured Electrocochleography (ECochG) signal; and determining that a disturbed basilar membrane wave propagation in the area from the selected first electrode contact to the selected second electrode contact exists based at least in part when the first phase-shift and second phase-shift differ by more than a predetermined threshold; and providing a signal representative of the determined disturbed basilar membrane wave propagation.

11. A system for detecting a disturbed basilar membrane wave propagation according claim 10, wherein the control unit is adapted to apply a predetermined threshold which includes a phase-shift between the first electrode contact and second electrode contact when no disturbed basilar membrane wave propagation is present.

12. A system for detecting a disturbed basilar membrane wave propagation according claim n, wherein the system includes a memory for storing averaged phase-shifts between electrode contacts representing phase-shifts when no disturbed basilar membrane wave propagation is present.

13. A system for detecting a disturbed basilar membrane wave propagation according to any of claims 10 to claim 12, wherein the predetermined threshold is at least 90 degrees or at least 180 degrees.

14. A system for detecting a disturbed basilar membrane wave propagation according to any of claims 10 to claim 12 further comprising an transducer adapted for placement close to the outer ear of the patient and operatively coupled to the control unit and the control unit further adapted to provide a control signal to the transducer, such that the transducer emits an acoustic signal.

15. A system for detecting a disturbed basilar membrane wave propagation according to claim 14, wherein the control signal is adapted such that the emitted acoustic signal has a certain frequency.

16. A system for detecting a disturbed basilar membrane wave propagation according to claim 15, wherein the frequency is any of 500Hz, 1000Hz or 2000Hz.

17. A system for detecting a disturbed basilar membrane wave propagation according to claim 14, wherein the control unit is further adapted for determining a control signal for the transducer based at least in part on the signal representative of the determined disturbed basilar membrane wave propagation.

18. A system for detecting a disturbed basilar membrane wave propagation according to claim 17, wherein determining a control signal based at least in part on the signal representative of the determined disturbed basilar membrane wave propagation includes the tonotopic location associated with the disturbed basilar membrane wave propagation.

19. A system for detecting a disturbed basilar membrane wave propagation according to claim 18, wherein the system further comprises an insertion detection unit adapted forproviding an insertion location information of the electrode array in the patient inner ear and the control unit is further adapted to estimate the tonotopic location based on the electrode array insertion location information.

20. A system for detecting a disturbed basilar membrane wave propagation according to any of the claims 10 to 19, wherein the system further comprises an output unit for providing to a user the signal representative of the determined disturbed basilar membrane wave propagation so as to indicate disturbed basilar membrane wave propagation and / or indicate the area of disturbed basilar membrane wave propagation.

21. A system for monitoring the insertion of an electrode array into an inner ear of a patient, the system comprising an output unit, an insertion detection unit adapted for providing an insertion location information of the electrode array in the patient inner ear, a measurement unit for measurement of the Electrocochleography (ECochG) signal of an electrode contact of an electrode array located in the inner ear of a patient and a control unit adapted for carrying out the steps of measuring with the measurement unit for at least a subset of electrode contacts of an electrode array located in the inner ear of a patient a Electrocochleography (ECochG) signal when an acoustic signal of a predetermined frequency is applied to the outer ear of the patient; selecting a first electrode contact and a second electrode contact based at least in part on a peak amplitude of the measured Electrocochleography (ECochG) signals; and determining a first phase-shift for the selected first electrode contact and a second phase-shift for the selected second electrode contact from the associated measured Electrocochleography (ECochG) signal; and determining that a disturbed basilar membrane wave propagation in the area from the selected first electrode contact to the selected second electrode contact exists based at least in part when the first phase-shift and second phase-shift differ by more than a predetermined threshold; and providing on the output unit a signal representative of the determined disturbed basilar membrane wave propagation.

22. A system for monitoring the insertion of an electrode array into an inner ear of a patient according to claim 21, wherein the control unit is further adapted to estimate the tonotopic location associated with the disturbed basilar membrane wave propagation based on the electrode array insertion location information and providing on the output unit the tonotopic location information.

23. A system for monitoring the insertion of an electrode array into an inner ear of a patient according to claim 21 or claim 22, further comprising a transducer adapted for placement close to the outer ear of the patient and operatively coupled to the control unit and the control unit further adapted to provide a control signal to the transducer, such that the transducer emits an acoustic signal.

24. A system for monitoring the insertion of an electrode array into an inner ear of a patient according to any of claims 21 to claim 23, the control unit is further adapted for determining a control signal for the transducer based at least in part on the signal representative of the determined disturbed basilar membrane wave propagation.

25. A system for detecting a disturbed basilar membrane wave propagation according to claim 24, wherein determining a control signal based at least in part on the signal representative of the determined disturbed basilar membrane wave propagation includes the tonotopic location associated with the disturbed basilar membrane wave propagation.

26. A system for detecting a disturbed basilar membrane wave propagation according to claim 24, wherein the system further includes a user input unit through which the user can adapt at least in part the predetermined threshold.

27. A system for detecting a disturbed basilar membrane wave propagation according to any of claims 21 to claim 26, wherein the predetermined threshold includes a phaseshift between the first electrode contact and second electrode contact when no disturbed basilar membrane wave propagation is present.

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