COMPENSATION FOR THE MIDDLE-EAR IMPEDANCE MISMATCH IN OTOACOUSTIC-EMISSION MEASUREMENTS

Abstract

Disclosed herein are embodiments of a device for measuring otoacoustic emissions (OAE) of a test subject. The device includes a stimulus generator configured to generate at least one acoustic stimulus, an ear probe, where the ear probe includes an output unit for emitting said at least one acoustic stimulus into an ear canal of the test subject, and an input unit for measuring an acoustic emission (P.sub.spl) from the ear of the test subject. The device can further include an analysis unit configured to receive said measured acoustic emission (P.sub.spl) and to determine a compensated pressure level (P.sub.npl) of said measured acoustic emission (P.sub.spl), where the determination of the compensated pressure level is based on characterizing the middle ear of the test subject as a Norton-equivalent circuit. The present application further relates to a method of measuring otoacoustic emissions (OAE) of a test subject and to a computer program.

Claims

1. Device for measuring otoacoustic emissions (OAE) of a test subject, the device comprising: a stimulus generator configured to generate at least one acoustic stimulus, an ear probe connected to said stimulus generator, where the ear probe comprises an output unit for emitting said at least one acoustic stimulus into an ear canal of the test subject, and an input unit for measuring an acoustic emission (P.sub.spl) from the ear of the test subject, and an analysis unit connected to the ear probe, where the analysis unit is configured to receive said measured acoustic emission (P.sub.spl), and to determine a compensated pressure level (P.sub.npl) of said measured acoustic emission (P.sub.spl), where the middle ear of the test subject is characterized as a Norton-equivalent circuit in the determination of the compensated pressure level (P.sub.npl).

2. Device according to claim 1, wherein determination of the compensated pressure level (P.sub.npl) is based on compensating for the test subject's ear canal acoustics, the effect of the middle ear of the test subject, and/or for the ear probe insertion position on the acoustic emission (P.sub.spl).

3. Device according to claim 1, wherein determination of the compensated pressure level (P.sub.npl) is based on said measured acoustic emission (P.sub.spl), a reflectance of the ear canal (R.sub.ec), a source reflectance of the ear probe (R.sub.s), and a one-way propagation coefficient (T) of the ear canal.

4. Device according to claim 1, wherein the term, characterizing the middle ear of the test subject as a Norton-equivalent circuit, comprises determining a compensated pressure level in dependence of a factor, (T.sup.2+R.sub.ec).sup.?1.

5. Device according to claim 3, wherein the device is further configured to determine said reflectance of the ear canal (R.sub.ec) and/or said one-way propagation coefficient (T) of the ear canal by: emitting at least one calibration stimulus, generated by the stimulus generator, into the ear canal of the test subject, via said output unit, measuring an acoustic calibration response from the ear canal, via the input unit, and determining said reflectance of the ear canal (R.sub.ec) and/or said one-way propagation coefficient (T) of the ear canal, based on said measured acoustic calibration response, by the analysis unit.

6. Device according to claim 1, wherein the compensated pressure level (P.sub.npl) of said measured acoustic emission represents the sound pressure that would be emitted into an anechoic ear canal were the tympanic membrane is an ideal flow source.

7. Device according to claim 1, wherein determination of the compensated pressure level (P.sub.npl) comprises calculating, at a plurality of frequencies, said compensated pressure level (P.sub.npl) by the equation: $P_{\mathrm{npl}}=P_{\mathrm{spl}}\frac{2T\left(1-R_{\mathrm{ec}}{R}_s\right)}{\left(1+R_s\right)\left(T^2+R_{\mathrm{ec}}\right)}$

8. Method of measuring otoacoustic emissions (OAE) of a test subject, the method comprising: generating at least one acoustic stimulus, by a stimulus generator, emitting the at least one acoustic stimulus into the ear canal of the test subject, by an output unit of an ear probe, measuring an acoustic emission (P.sub.spl) from the ear of the test subject, by an input unit of the ear probe, receiving said measured acoustic emission (P.sub.spl), by an analysis unit, and determining a compensated pressure level (P.sub.npl) of said measured acoustic emission (P.sub.spl), by the analysis unit, where the middle ear of the test subject is characterized as a Norton-equivalent circuit in the determination of the compensated pressure level (P.sub.npl).

9. Method according to claim 8, wherein characterizing the middle ear of the test subject as a Norton-equivalent circuit comprises determining a compensated pressure level in dependence of a factor (T.sup.2+R.sub.ec).sup.?1, where T is a one-way propagation coefficient of the ear canal and R.sub.ec is a reflectance of the ear canal.

10. Method according to claim 8, wherein the method further comprises determining the reflectance of the ear canal (R.sub.ec) and/or the one-way propagation coefficient (T) of the ear canal by: emitting at least one calibration stimulus, generated by the stimulus generator, into the ear canal of the test subject, via said output unit, easuring an acoustic calibration response from the ear canal, via the input unit, and determining said reflectance of the ear canal (R.sub.ec) and/or said one-way propagation coefficient (T) of the ear canal, based on said measured acoustic calibration response, by the analysis unit.

11. Method according to claim 8, wherein determination of the compensated pressure level (P.sub.npl) comprises calculating, at a plurality of frequencies, said compensated pressure level (P.sub.npl) by the equation: $P_{\mathrm{npl}}=P_{\mathrm{spl}}\frac{2T\left(1-R_{\mathrm{ec}}{R}_s\right)}{\left(1+R_s\right)\left(T^2+R_{\mathrm{ec}}\right)}$

12. A computer program comprising instructions which, when the program is executed by a device, cause the device to carry out the steps of the method according to claim 8.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0093] The aspects of the disclosure may be best understood from the following detailed description taken in conjunction with the accompanying figures. The figures are schematic and simplified for clarity, and they just show details to improve the understanding of the claims, while other details are left out. Throughout, the same reference numerals are used for identical or corresponding parts. The individual features of each aspect may each be combined with any or all features of the other aspects. These and other aspects, features, and/or technical effect will be apparent from and elucidated with reference to the illustrations described hereinafter in which:

[0094] FIG. 1 shows an exemplary device according to the present application.

[0095] FIG. 2 shows the possible varying insertion locations and positions of an ear probe.

[0096] FIGS. 3A and 3B show measurements of the reflectance and of OAEs, respectively.

[0097] FIG. 4 shows exemplary relative OAE response magnitudes and phases in an occluded-ear simulator.

[0098] The figures are schematic and simplified for clarity, and they just show details which are essential to the understanding of the disclosure, while other details are left out. Throughout, the same reference signs are used for identical or corresponding parts.

[0099] Further scope of applicability of the present disclosure will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the disclosure, are given by way of illustration only. Other embodiments may become apparent to those skilled in the art from the following detailed description.

DETAILED DESCRIPTION OF EMBODIMENTS

[0100] The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. Several aspects of the device and methods are described by various blocks, functional units, modules, components, circuits, steps, processes, algorithms, etc. (collectively referred to as elements). Depending upon particular application, design constraints or other reasons, these elements may be implemented using electronic hardware, computer program, or any combination thereof.

[0101] FIG. 1 shows an exemplary device according to the present application.

[0102] In FIG. 1, the device 1 is shown to be located at and/or in connection with the head 2 of a test subject.

[0103] The device 1 may be configured to assess the health of the cochlea of a test subject. For example, the device 1 may be suitable for measuring otoacoustic emissions (OAE) of a test subject.

[0104] The device 1 is shown to comprise two elements, but may of course be combined to only one element, or alternatively be divided into several elements.

[0105] In FIG. 1, a first element of the device 1 may be arranged inside the ear canal 3 of the test subject. Alternatively, or additionally, the first element may be arranged at least partly outside the ear canal 3. The first element is shown to be an ear probe 4 suitable for insertion into the ear canal 3.

[0106] The ear probe 4 may comprise an ear tip 5, which may be releasably attached to an ear-probe body 6. When the ear probe 4 has been inserted correctly into the ear canal 3, the ear tip 5 may provide a barometric seal toward the ear-canal walls 7 of the ear canal 3. The device 1 may (via the ear probe 4) provide at least one stimulus (e.g., an acoustic stimulus or a calibration stimulus) into the ear canal 3 of the test subject 2 in a direction towards the eardrum 8 and receive a reflected part of said stimulus and/or an otoacoustic emission, as indicated by the two arrows in the ear canal 3.

[0107] A second element of the device 1 is shown to be arranged outside the ear canal 3 of the test subject 2. Alternatively, or additionally, the second part (or at least some elements of the second part) could be combined with the ear probe 4.

[0108] The device 1 may comprise a stimulus generator 9. The stimulus generator 9 may be configured to generate at least one acoustic stimulus. Said acoustic stimulus may be introduced/emitted into the ear canal 3 of the test subject 2 via an output unit 10 (e.g., comprising a speaker 11) of the ear probe 4.

[0109] The ear probe 4 may comprise an input unit 12 (e.g., comprising a microphone 13). The input unit 12 may be configured to measure an acoustic emission (P.sub.spl) from the ear of the test subject 2, and may be configured to provide an electrical input signal in dependence of the acoustic emission.

[0110] The device 1 may comprise an analysis unit 14. The analysis unit 14 may be connected to the ear probe 4, and may be configured to receive the measured acoustic emission (P.sub.spl) from said input unit 12. The analysis unit 14 may be configured to determine a compensated pressure level (P.sub.npl) of said measured acoustic emission (P.sub.spl), where the determination of the compensated pressure level is based on characterizing the middle ear of the test subject 2 as a Norton-equivalent circuit.

[0111] As indicated in FIG. 1, the second element of the device 1 may be connected to the first element. The first and second elements may be connected by a wired or a wireless connection 15, or may alternatively form one unit.

[0112] FIG. 2 shows the possible varying insertion locations and positions of an ear probe.

[0113] Determination of a compensated pressure level (P.sub.npl) may be based on compensating for the test subject's ear-canal acoustics. For example, a test subject's ear-canal acoustics may vary depending on the position and orientation of the ear probe 4. For example, monitoring for ototoxic drugs may cause OAE responses to deteriorate over time for which reason such monitoring process requires that an OAE response can be accurately reproduced.

[0114] Further, standing waves between the tympanic membrane 8, where an OAE enters the ear canal 3, and the ear probe 4 may influence the OAE response, resulting in amplification of the OAE response near resonance frequencies. The result is that OAE responses may vary significantly when the ear probe 4 is not placed in the exact same location between measurement sessions.

[0115] In FIG. 2, it is illustrated that the ear probe 4 may unintentionally be inserted at different distances from the tymphanic membrane 8. This is illustrated by the distances L1, L2, and L3, which makes reproducibility of the OAE test difficult.

[0116] Also, as illustrated in FIG. 2, the ear probe 4 (and in particular the ear-probe body 6) may be positioned at a varying angle ? from test to test, which makes reproducibility of the OAE test difficult.

[0117] FIGS. 3A and 3B show measurements of the reflectance and of OAEs, respectively.

[0118] In FIG. 3A, a calibration stimulus may be emitted into the ear canal 3 of the test subject. The type and sound pressure level of said calibration stimulus may be sufficient to primarily being reflected by the ear canal 3 (i.e., the tympanic membrane 8 and the ear canal walls 7). Thereby, the reflectance R.sub.ec can be measured based on the calibration stimulus emitted by the ear probe 4.

[0119] In FIG. 3B, at least one acoustic stimulus may be emitted into the ear canal 3 of the test subject. The type and sound-pressure level of said acoustic stimulus may be sufficient for primarily evoking OAEs in the cochlear 16 of the test subject. Thereby, OAEs may be measured based on said acoustic stimulus.

[0120] FIG. 4 shows exemplary relative OAE response magnitudes and phases in an occluded-ear simulator.

[0121] To illustrate the merits of the Norton pressure level, the simulated OAE response in an occluded-ear simulator was measured (similar to [2]). That is, a reference microphone at the coupler termination (representing the tympanic membrane) is operated as an electrostatic speaker. The reference coupler microphone can now be approximated as an ideal displacement source which, when scaled by 1/(j?), acts as an ideal flow source, i.e., the Norton flow level U.sub.nfl. The ear probe was calibrated according to [4][5] and the ear-canal reflectance measured according to [6].

[0122] FIG. 4 shows the relative OAE response magnitudes and phases, i.e., scaled by 1/(U.sub.nfl Z.sub.0). [3] provides a detailed investigation of the impact of insertion depth and ear-probe insertion angle on the ear-canal pressure level P.sub.spl and emitted pressure level P.sub.epl.

[0123] It is illustrated how the measured OAE response P.sub.spl (blue curve) without any compensation is amplified by the compliance of the ear canal at low frequencies and by standing waves at 7 and 14 kHz. When the insertion of the ear probe varies, these resonances are translated in frequency and the OAE response changes.

[0124] The emitted pressure level P.sub.epl (red curve) is unaffected by the ear-canal acoustics, but remains effected by the simulated middle-ear impedance in the occluded-ear simulator. This is evident from the 2 dB decrease in relative OAE response at 1 and 3 kHz.

[0125] The Th?venin pressure level P.sub.tpl (yellow curve) is unaffected by the middle-ear impedance per se, but varies significantly with minor measurement errors and variations in the ear-canal propagation coefficient T.

[0126] The Norton pressure level P.sub.npl is largely comparable to the emitted pressure level P.sub.epl in the occluded-ear simulator, but is unaffected by the middle-ear resonances at 1 and 3 kHz. In real ears, where one might encounter middle-ear impedances with lower magnitudes, the difference between P.sub.epl and P.sub.npl may by larger.

[0127] An advantage of the emitted pressure level P.sub.epl is that its magnitude is independent of the estimated ear-canal length constituted in the variable T. On the other hand, the Th?venin pressure level P.sub.tpl is extremely sensitive to errors in ear-canal propagation coefficient. This is due to the factor T.sup.2?R.sub.ec in its denominator because identical delays, resulting primarily from the ear-canal length, are encoded into T.sup.2 and R.sub.ec. Conversely, although the Norton pressure level is affected by errors in the ear-canal propagation coefficient, it is to a much lesser degree because the factor in the denominator reads T.sup.2+R.sub.ec. Furthermore, the Norton pressure level P.sub.npl phase appears to be less sensitive to small length errors than the emitted pressure level P.sub.epl phase.

[0128] It is intended that the structural features of the devices described above, either in the detailed description and/or in the claims, may be combined with steps of the method, when appropriately substituted by a corresponding process.

[0129] As used, the singular forms a, an, and the are intended to include the plural forms as well (i.e., to have the meaning at least one), unless expressly stated otherwise. It will be further understood that the terms includes, comprises, including, and/or comprising, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It will also be understood that when an element is referred to as being connected or coupled to another element, it can be directly connected or coupled to the other element, but an intervening element may also be present, unless expressly stated otherwise. Furthermore, connected or coupled as used herein may include wirelessly connected or coupled. As used herein, the term and/or includes any and all combinations of one or more of the associated listed items. The steps of any disclosed method are not limited to the exact order stated herein, unless expressly stated otherwise.

[0130] It should be appreciated that reference throughout this specification to one embodiment or an embodiment or an aspect or features included as may means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. Furthermore, the particular features, structures or characteristics may be combined as suitable in one or more embodiments of the disclosure. The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects.

[0131] The claims are not intended to be limited to the aspects shown herein but are to be accorded the full scope consistent with the language of the claims, wherein reference to an element in the singular is not intended to mean one and only one unless specifically so stated, but rather one or more. Unless specifically stated otherwise, the term some refers to one or more.

REFERENCES

[0132] [1] Charaziak, K. K., & Shera, C. A. (2017). Compensating for ear-canal acoustics when measuring otoacoustic emissions. J. Acoust. Soc. Am. 141(1), 515-531. [0133] [2] Allen, J. B. (1986). Measurement of eardrum acoustic impedance. In J. Allen, J. Hall, A. Hubbard, S. Neely, & A. Tubis (Eds.), Peripheral Auditory Mechanisms (pp. 44-51). Springer-Verlag. [0134] [3] N?rgaard, K. R., Charaziak, K. K., & Shera, C. A. (2019). A comparison of ear-canal-reflectance measurement methods in an ear simulator. J. Acoust. Soc. Am. 146(2), 1350-1361. [0135] [4] N?rgaard, K. R., Fernandez-Grande, E., & Laugesen, S. (2017). Incorporating evanescent modes and flow losses into reference impedances in acoustic Th?venin calibration. J. Acoust. Soc. Am. 142(5), 3013-3024. [0136] [5] N?rgaard, K. R., Fernandez-Grande, E., & Laugesen, S. (2018). A coupler-based calibration method for ear-probe microphones. J. Acoust. Soc. Am. 144(4), 2294-2299. [0137] [6] N?rgaard, K. R., Fernandez-Grande, E., & Laugesen, S. (2019). Compensating for oblique ear-probe insertions in ear-canal reflectance measurements. J. Acoust. Soc. Am. 145(6), 3499-3509.