Optical coherence tomography device for otitis media

Abstract

To provide a favorable optical coherence tomography device for otitis media.SOLUTION: An OCT apparatus and method for characterization of a fluid adjacent to a tympanic membrane has a low coherence source which is coupled to a splitter which has a measurement path and a reference path. The reference path is temporally modulated for length, and combined signals from the reference path and the measurement path are applied to a detector. The detector examines the width of the response and the time variation when an optional excitation source is applied to the tympanic membrane, where the width of the response and the time variation form a metric indicating the viscosity of a fluid adjacent to the tympanic membrane being measured.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to optical coherence tomography (OCT), and in particular to OCT for use in the diagnosis of otitis media (OM). [Background technology]

[0002] Otitis media is a common disease of the inner ear involving tissue inflammation and fluid pressure affecting the eardrum. Otitis media can be caused by a viral infection, which generally resolves without treatment, or a bacterial infection, which can progress and cause hearing loss or other harmful and irreversible effects. Unfortunately, it is difficult to distinguish between viral and bacterial infections using currently available diagnostic devices, and treatment methods for the two underlying infections are quite different. While antibiotics are the treatment of choice for bacterial infections, for viral infections, the infection tends to self-resolve, and antibiotics are not only ineffective but can also lead to antibiotic resistance, making them less effective in treating subsequent bacterial infections.

[0003] The definitive diagnostic tool for inner ear infections is the invasive procedure, myringotomy, which involves opening the eardrum, withdrawing fluid, and examining the exudate under a microscope to identify infectious agents in the exudate. Due to complications from this procedure, it is only used in severe cases. This presents a dilemma for medical practitioners because prescribing antibiotics for viral infections is thought to be responsible for the development of antibiotic resistance in bacteria, which can lead to more serious consequences later in life, and treating viral infectious agents with antibiotics is ineffective if not accompanied by effective results. Improved diagnostic tools for diagnosing otitis media are desirable. Summary of the Invention [Means for solving the problem]

[0004] (Object of the present invention) A first object of the present invention is a non-invasive medical device for the identification of fluid types adjacent to the tympanic membrane.

[0005] A second object of the present invention is a method for the identification of fluid adjacent to the tympanic membrane.

[0006] A third object of the present invention is a method for performing optical coherence tomography for the identification of thin film properties adjacent to the tympanic membrane.

[0007] A fourth object of the present invention is an apparatus for performing optical coherence tomography for identification of fluid properties adjacent to the tympanic membrane.

[0008] A fifth object of the present invention is an apparatus and method for characterizing the tympanic membrane and adjacent materials by coupling a pressure excitation source to the tympanic membrane, wherein the tympanic membrane is illuminated through a measurement path by an optical source having low coherence, the low coherent optical source also being coupled to a reference path and a mirror, wherein reflections from the mirror and from the tympanic membrane are summed and presented to a detector, the reference path length being modulated over a range that includes the tympanic membrane, and the detector receiving reflected optical energy from the tympanic membrane through the measurement path and from the mirror through the reference path, such that modulation of the reference path length at a sufficiently high rate allows estimation of the tympanic membrane position in response to the pressure excitation, thereby providing characterization of the tympanic membrane and adjacent fluid.

[0009] A sixth object of the present invention is an optical coherence tomography system having a measurement path and a reference path, wherein the reference path is modulated in length, and the measurement path and the reference path are coupled to an optical source having low coherence through an optical splitter, and optical energy reflected from the reference optical path and the optical energy reflected from the measurement optical path are summed and provided to a wavelength splitter and then to a plurality of detectors, one detector for each sub-range of wavelengths within the wavelength spectrum of the low coherence optical source, and the plurality of detectors are coupled to a controller that distinguishes detector responses for at least two different reflective materials by their wavelength characteristics. (Summary of the Invention)

[0010] The optical coherence tomography (OCT) device has a low-coherence optical source that generates optical energy that is coupled through a first splitter and then to a second splitter. The second splitter has a measurement optical path to the tympanic membrane and a reference optical path to a reflector that returns the optical energy to the first splitter, where the reflected optical energy is added to the optical energy reflected from the measurement optical path. The combined reflected optical energy is then provided to the first splitter, which directs the optical energy to a detector. The reflector is displaced and spatially modulated along the axis of the reference optical path so that when the path lengths of the measurement optical path and the reference optical path are equal, the detector exhibits optical intensity from a specific measurement path depth and, optionally, a range of optical spectral densities. When the device is positioned with the measurement path directed into the ear canal and directs optical energy to the tympanic membrane by varying the reference optical path length through translation of the reflector location along the axis of the reference optical path, measurements of the tympanic membrane's optical and spectral properties can be performed. Additionally, an external pressure excitation can be applied to provide impulse or steady-state periodic excitation of the tympanic membrane during OCT measurements, and the peak response and associated time of the peak response can be identified. The temporal characteristics and positional displacement of the tympanic membrane can then be examined to determine the tympanic membrane response to the external pressure excitation. Evaluation of the tympanic membrane response from the OCT detector data can then be correlated with specific viscosity or biofilm properties. By examining the temporal characteristics, an estimate of the viscosity of the fluid adjacent to the tympanic membrane can be determined, and the viscosity can then be correlated with the likelihood of a treatable bacterial infection. The present specification provides, for example, the following: (Item 1) 1. A method for characterization of a fluid adjacent to a reflective membrane, the method comprising: providing a low-coherence optical source to a first splitter, wherein a portion of the optical energy is directed into a measurement path and a portion of the optical energy is directed into a reference path; the reference path having a time-modulated length, thereby varying the reference path length over periodic intervals; the measurement path includes a reflective film to be characterized, the reference path has a length substantially equal to the measurement path, the reference path also including a reflector for reflecting optical energy; summing the optical energy reflected from the measurement path and the optical energy reflected from the reference path and applying the summed optical energy to a detector; the detector providing a detector peak response to the reference path modulator to the controller; the controller examines a pedestal width of a detector response and an arrival time of the detector peak response; comparing the current peak detector response with a previous peak detector response; forming a tympanic membrane metric from the current peak detector response and a previous peak detector response, the tympanic membrane metric increasing as the pedestal width increases and the tympanic membrane metric increasing as the variance in arrival times of the detector peaks decreases; A method comprising: (Item 2) Item 10. The method of item 1, wherein the reference path and the measurement path are free-space optical paths formed by fully reflective and partially reflective mirrors. (Item 3) Item 10. The method of claim 1, wherein the reference path and the measurement path are formed by waveguides. (Item 4) Item 10. The method according to item 1, wherein the reference path and the measurement path are formed by optical fibers. (Item 5) Item 10. The method of item 1, wherein the low coherence source is a light emitting diode. (Item 6) Item 10. The method of claim 1, wherein the detector is an optical / electrical converter. (Item 7) Item 10. The method of claim 1, wherein the detector has multiple wavelength-specific outputs. (Item 8) Item 10. The method of item 1, wherein the temporally modulated length comprises a voice coil actuator coupled to a mirror. (Item 9) Item 10. The method of item 1, wherein the temporally modulated length is a PZT activated modulator. (Item 10) 8. The method of claim 7, wherein the plurality of wavelength-specific outputs are coupled to the template memory for comparison of the detector response with wavelength responses of various material types stored in the template memory. (Item 11) Item 11. The method of item 10, wherein at least one of the template memory material types is a reflex response related to earwax. (Item 12) Item 12. The method of item 11, wherein the detection of earwax generates an indication of earwax detection to a user. (Item 13) A device for measurement of the tympanic membrane, said device comprising: an optical source generating a low-coherence optical output; a first splitter and a second splitter, each splitter having a combiner port, a first port, and a second port, each splitter coupling power from the first port to the combiner port and from the combiner port to the second port; the optical source is coupled to a first port of the first splitter; a combiner port of the first splitter coupled to a combiner port of the second splitter; the first port of the second splitter couples optical energy to an external optical port and to a film to be characterized, the optical distance from the film to be characterized to the first port of the second splitter being a measurement length; a second port of the second splitter coupled to an optical reference path having an optical length modulated about a measurement optical length; a splitter whereby optical energy reflected from the external optical port is directed through a combiner port of the second splitter to a combiner port of the first splitter, a second port of the first splitter, and a detector; a controller that receives a signal from the detector and compares a current detector response with a previous detector response to form a reflectance metric; A device having: (Item 14) Item 14. The device of item 13, wherein the low coherence source is a light emitting diode. (Item 15) Item 14. The device according to item 13, wherein the detector is a broadband detector. (Item 16) Item 14. The device of item 13, wherein the detector has multiple outputs, each output responsive to a unique wavelength range. (Item 17) Item 14. The device of item 13, wherein the first splitter and the second splitter are partially reflective mirrors. (Item 18) Item 14. The device of item 13, wherein the first splitter and the second splitter are optical fibers. (Item 19) Item 14. The device of item 13, wherein the controller forms an exudation metric based on at least one of a detector response width, a pedestal width, or a reflected wavelength profile. (Item 20) Item 14. The device of item 13, wherein the optical length of the reference path is modulated using an actuator that controls a voltage or current coupled to a mirror. (Item 21) Item 14. The device of item 13, wherein the optical length of the reference path is modulated using a PZT actuator coupled to an optical fiber. (Item 22) Item 16. The device of item 15, wherein the plurality of detectors, which are broadband detectors, includes a template memory for comparison of the plurality of detector responses to known biological materials. (Item 23) 23. The device of claim 22, wherein at least one of the template memory detector responses is earwax, a healthy tympanic membrane, an inflamed tympanic membrane, bacterial fluid, exudate fluid, or adhesive fluid. [Brief explanation of the drawings]

[0011] [Figure 1] Figure 1 shows a block diagram of the optical coherence tomography characterization system. [Figure 2A] FIG. 2A shows a plot of mechanical actuator displacement versus actuator voltage. [Figure 2B] FIG. 2B shows a plot of the reference path length over time as controlled by the actuator voltage or current. [Figure 3] Figure 3 shows a block diagram for an optical coherence tomography characterization system for use in examining the tympanic membrane. [Figure 4] FIG. 4 shows a polychromatic detector. [Figure 5] Figure 5A shows a plot of an exemplary excitation waveform for modulation of the reference length, and Figure 5B shows the detector signal for a tympanic membrane adjacent to fluid from an OME and a normal tympanic membrane. [Figure 6] Figure 6 shows an optical waveguide system for measurements on the eardrum. [Figure 7] FIG. 7 shows an optical waveguide system for measurements on the eardrum, along with an excitation source. [Figure 8A] FIG. 8A shows a plot of a sinusoidal excitation applied to a deformable surface or membrane along with the reflected response signal. [Figure 8B] FIG. 8B shows a plot of a step excitation applied to a deformable surface or membrane and the response to the step excitation. DETAILED DESCRIPTION OF THE INVENTION

[0012] 1 shows a block diagram for an optical coherence tomography (OCT) device according to one embodiment of the present invention. Each reference number appearing in one drawing will be understood to have the same function when presented in a different drawing. A low-coherence source 102, such as a broadband light-emitting diode (LED) with a collimated output, generates optical energy along path 104 to a first optical splitter 106, which continues to a second optical splitter 108, where it splits into a measurement optical path 118 and a reference optical path 112, which includes a section from the second splitter 108 to a mirror 110 and to a path length modulator 114. The optical energy in the measurement optical path 118 interacts with the tympanic membrane 120, and the reflected optical energy propagates back to the detector via path 118, where it is combined with the optical energy from the reference optical path 112 reflected from mirror 110 and splitter 108. The combined reflected optical energy propagates to the first splitter 106, then to mirror 105, and via path 122 to the detector 124. The detector 124 generates an electrical signal corresponding to the intensity of the detected optical energy on path 122, which has a steady-state maximum when the path length for the optical energy reflected from the tympanic membrane is exactly the same length as the reference optical path, and a transient maximum when the reference optical path length is swept over a range, such as by actuating the path length modulator 114 over time. Each type of reflective membrane will produce a characteristic detector signal. For example, as the reference path length traverses through a thin membrane boundary, such as a healthy tympanic membrane, a single peak will result, corresponding to a single reflective region of the tympanic membrane. If the reference path length passes through a fluid ear, such as one containing a low-viscosity infectious exudate, an initial peak in the tympanic membrane reflection will be followed by a region of extended reflection, with amplitudes that drop off from the optical attenuation of the reflected signal. If the reference path length traverses through a tympanic membrane with a bacterial infection, a bacterial film may be present on the opposite surface of the tympanic membrane, which may result in a larger axial reflection range, followed by a pedestal exhibiting a high scattering coefficient and corresponding increased attenuation.Additionally, the three types of fluid viscosities behind the tympanic membrane (air vs. thin fluid vs. thick fluid) will respond differently to pressure excitation generated on the tympanic membrane. Thus, by modulating the reference optical path length and optionally the pressure adjacent to the tympanic membrane and examining the nature of the detector output signal and its response to excitation pressure, it is possible to determine the presence or absence of fluid adjacent to the tympanic membrane, the presence or absence of a biofilm such as bacteria adjacent to the tympanic membrane, and the viscosity of the fluid adjacent to the tympanic membrane, all resulting from movement of the tympanic membrane on the measurement optical path as presented in the detector output.

[0013] In one embodiment of the invention, path length modulator 114 varies the reference path length by a distance corresponding to the measurement path length from 126a to 126d in Figure 1, which corresponds to the region of movement of tympanic membrane 115 to be characterized. As modulator 114 increases the reference path length, the signal delivered to the detector is closer to region 126d, and when modulator 114 decreases the distance of the reference path length, the region signal delivered to the detector is within region 126a.

[0014] 2A shows an example relationship between actuator voltage or current and axial displacement of path length modulator 114, which is driven by mechanical driver circuit 116, which may be a voice coil driver for a voice coil actuator coupled to mirror 114 and modulating the mirror about the optical axis of 112. The type of driver and path length modulator 114 depends on the highest frequency of displacement modulation because the energy to displace path length modulator 114 is related to the mass of path length modulator 114, as in the case of a moving mirror. The mirror and actuator may be microelectromechanical systems (MEMS) for lower reflector mass and correspondingly faster mirror response. Without being limited to the use of mirrors, various other path length modulators may be utilized.

[0015] 2B shows controller 117 generating actuator voltages in a stepped manner, with the actuator temporarily deactivating at each depth. For example, if increased actuator drive results in a longer reference path length from T1 to T2, the actuator voltage may be 202a, corresponding to displacement position 126a in FIG. 1, and other voltages 202b, 202c, and 202d may correspond to positions adjacent the tympanic membrane at 126b, 126c, and 126d, respectively.

[0016] Figure 3 shows an exemplary OCT tympanic membrane characterization system 302 with elements arranged to provide a single measurement output. For free-space optics (optical energy not confined within a waveguide such as an optical fiber), the system splitters and combiners of Figures 1 and 3 are partially reflecting mirrors. The main elements shown in Figure 3 correspond to the same functional elements in Figure 1. By rearranging the reference optical path, the elements of the system may be encapsulated as shown.

[0017] In one embodiment of the present invention, detector 124 may be a single, all-wavelength optical detector having a characteristic response responsive to the total applied optical intensity. In another embodiment of the present invention, detector 124 may include a single wavelength filter or chromatic splitter and multiple detector elements so that each reflected optical wavelength can be detected separately. FIG. 4 shows collimated optical energy 122 entering chromatic detector 124A, where it is split into different wavelengths by refractive prism 124B, which separates wavelengths λ1, λ2, λ3, and λ4 onto linear or 2D detector 124C, which can then provide an intensity map of the reflected optical energy by wavelength. Individual detection of wavelengths may be useful when wavelength absorption signatures are unique to particular types of bacteria or tympanic membrane pathologies. The spectrum of the detector response is tuned to the reflected optical energy response, which may typically be in the IR range for OCT systems with depth measurement capabilities greater than a few millimeters. In one embodiment of the present invention, detector spectral responses for various biological materials are maintained in memory and compared to a superposition of responses from multiple optical detectors. For example, the optical reflectance characteristics of earwax (earwax), a healthy tympanic membrane, an inflamed tympanic membrane (a tympanic membrane infused with blood), bacterial fluid, exudate fluid, and adhesive fluid may be maintained in a template memory and compared to the spectral distribution of the tympanic membrane response measured across the axial depth of data acquisition. The detector response at each axial depth across a range of reference optical path lengths can then be compared by a controller to the spectral characteristics of each of the template memory spectral patterns, which examines the detector response for each wavelength and the contents of the template memory and, based on this determination, estimates the type of material providing the measurement path reflectance. Detection of a spectral pattern related to earwax may result in subtraction of the earwax spectral response from the detector response and / or provide an indication to the user that earwax has been detected in the response, which the user can eliminate by pointing the measurement optical path within a different region of the tympanic membrane.

[0018] Because the axial resolution of optical coherence tomography is a fraction of the optical wavelength, it is possible to characterize each of the imaged structures separately based on their optical spectra, even if each is only 100 microns axially thick. The axial resolution of the system can be improved by providing a very narrow optical beam with high spatial energy along the measurement axis and across the axial extent of the tympanic membrane.

[0019] 5A and 5B illustrate an embodiment of the present invention for use in detecting the position of the tympanic membrane over time. The controller 117 generates a triangular waveform 502 for use by the path-length modulator to direct optical energy toward the tympanic membrane, which may have fluid adjacent thereto. The fluid may have a particular viscosity, which may be known to increase during the progression of a bacterial infection. Bacterial infections are known to provide a biological thin film on the surface of a membrane, such as the tympanic membrane, with specific optical reflectance characteristics. An optical signal is directed through the outer ear canal toward the tympanic membrane to be characterized, and the detector response of FIG. 5B is examined by the controller 117 of FIG. 3. A first set of waveforms 509 shows a time-domain response, including an initial peak 507 associated with a strong reflection of the sharply reflective optical interface provided by the tympanic membrane at the first reflective interface; fluid behind the tympanic membrane also generates a signal that decays with depth, shown as a sloping pedestal 508. The presence of the pedestal 508 indicates the presence of fluid behind the tympanic membrane, which can be contrasted with a second set of responses 511 for a normal tympanic membrane, such as peaks in waveform 522, which are relatively narrow and of shortened duration 520 due to the absence of reflective fluid behind the tympanic membrane.

[0020] In additional embodiments of the present invention, the tympanic membrane itself may be modulated by an external excitation source, such as an air puff or air pressure source, modulated over time. If an external pressure excitation source is provided and the pressure excitation is selected to provide, for example, less than 1% displacement of the tympanic membrane, the relative temporal position of the peak optical signal will indicate the position of the tympanic membrane. Because the system's refresh rate is optical rather than acoustic as in prior art ultrasound devices, the interrogation speed of the tympanic membrane is limited only by the modulation rate of the path length modulator 114, which can be several times faster than ultrasound systems. In addition, the axial resolution of optical systems relying on optical interferometry far exceeds the axial resolution of ultrasound systems, which is governed by transducer ringdown. Additionally, because the acoustic impedance boundary between air and the tympanic membrane is very large, the ultrasonic penetration depth of ultrasound to structures beyond the tympanic membrane is very limited. In contrast, the optical refractive index ratio from air to the tympanic membrane is many times lower than the ultrasonic refractive index ratio across this boundary, and therefore optical energy loss at the interface is lower. Optical transmission is primarily limited by scattering losses associated with the tympanic membrane and structures beyond the tympanic membrane interface; these losses can be mitigated, in part, by using very high optical energies, pulsed with duty cycle modulation, to keep the average power applied to the tympanic membrane within a reasonable average power range.

[0021] 6 shows an optical fiber implementation of an optical coherence tomography system 600. A controller 618 coordinates various subsystems, including enabling a low-coherence source 602, which couples optical energy into an optical fiber 604, which then delivers the optical energy to a first splitter 606 and then to an optical fiber 608 and a second splitter 610. The optical energy from the second splitter 610 is directed into two paths: a measurement path 612 to the eardrum with a length L 615; and a reference optical path 617 with a length L 615 that terminates in an open reflective fiber end 619, which may alternatively be a mirror-polished end or an optical reflective end. The optical path 617 includes an optical fiber wrapped around a PZT modulator 614, which changes size, shape, and diameter when an excitation voltage is applied to the PZT. When the PZT modulator 614 is fed with a sinusoidal or square wave excitation, it increases and decreases its diameter, thereby providing a variable length Lref. The PZT modulator 614 is also capable of high-speed fiber length modulation at frequencies exceeding 100 Khz. Other fiber length modulators known in the art may also be used to rapidly change the length of the optical fiber on the Lref path; the PZT modulator 614 is shown for reference only. The combined optical energy from the Lmeas and Lref paths reaches the second splitter 610 and returns onto the fiber 608, constituting the sum of the optical energy reflected from the PZT modulator 614 and from the eardrum 650. The combined optical energy follows path 608 to first splitter 606, travels through fiber 620 to detector 622, where the coherent optical energy is superimposed and subtracted as appropriate to form a detector 622 output, which is fed to controller 618 for analysis.The controller 618 may also generate a PZT modulator excitation voltage 616, such as the voltage or current waveform 502 of FIG. 5A, and may also generate a signal to enable the low coherence source 602, and perform an analysis of the detector 622 response, which may be a single intensity value across the wavelength response of the detector 622 or the individual wavelength outputs provided by the sensor of FIG. 4. The controller, in combination with the Lref modulation function, operates on the detector response to determine an effusion metric that may be correlated to the likelihood that fluid is present adjacent the tympanic membrane and also provides an indication of the viscosity of the fluid adjacent the tympanic membrane.

[0022] 7 shows an extension of FIG. 6 with an external tympanic membrane excitation generator 704 that delivers fine pressure changes, preferably actuated by a voice coil actuator or other pressure source with a peak pressure below 50 decaPascals (daPa), for application to the tympanic membrane. The modulation of the reference path length by the PZT modulator 614 is at a rate that exceeds the highest frequency content of the excitation generator 704 by at least a factor of two to meet Nyquist sampling requirements.

[0023] In one embodiment of the present invention, the reference path length is modulated by a first modulator and a second modulator operating in series, with the first modulator providing a large but relatively slow reference path length change and the second modulator providing a small but relatively fast reference path length change. In this manner, the first modulator can be positioned within a region of interest for the OCT examination, such as centered on the tympanic membrane, and the second modulator can rapidly vary the path length and provide a high rate of change in path length (and therefore a high sampling rate) for estimation of tympanic membrane movement in response to pressure excitation.

[0024] In the tympanic membrane, shown as 115 in Figures 1 and 3 and 650 in Figures 6 and 7, the tympanic membrane is seen to have a conical shape with a distal apex (119 in Figures 1 and 3, 651 in Figures 6 and 7), which is known in otolaryngology as the "cone of light" because this is the only region of the tympanic membrane that provides a normal surface to the incident optical energy during clinical examination. Similarly, when using the ultrasound sources of prior art systems, the cone of light field is the only portion of the tympanic membrane that provides significant reflected signal energy. The optical system of the present invention operates on optical energy reflected from a surface, which does not need to be normal to the incident beam due to scattered optical energy, thereby providing another advantage over ultrasound systems.

[0025] FIG. 8A shows an example sinusoidal pressure excitation from excitation generator 704 applied to the tympanic membrane, such as a sinusoidal waveform 821 applied using a voice coil diaphragm actuator that displaces a volume sufficient to modulate a localized region of tympanic membrane or surface pressure by 100 daPa (decapascals) pp. Subsonic (below 20 Hz) frequencies may require sealing of the localized region around the excited surface, while audible (in the range of 20 Hz to 20 kHz) and infrasonic (above 20 kHz) frequencies may be sufficiently propagated as audible waves from generator 704 without sealing the ear canal leading to the tympanic membrane to be characterized. The sinusoidal pressure excitation 821 results in a modulation of the surface, shown as plot 832, where modulation in surface position corresponds to a change in the associated Lref path length by the same amount. Each discrete circle in waveform 832 represents a sample point from OCT measurement system 700 corresponding to a change in Lref path length and tympanic membrane position, with each point 332 representing one such sample. In one exemplary embodiment of the invention, a series of sinusoidally modulated excitation 821 frequencies are applied, each with a different period 822, and the delay of the response 830 and the peak change in Lref are used in combination to estimate the ductility or elasticity of the tympanic membrane, fluid viscosity, or other tympanic membrane or fluid properties. In this example, there is a 1:1 relationship between the tympanic membrane displacement and the associated change in the path length of the reference path, which results in a peak response. For example, if the scale in FIG. 5B is a sequence of 0, −0.5 mm, −1 mm, −0.5 mm, 0 mm, 0.5 mm, etc., this represents the corresponding displacement of the tympanic membrane at these same distances. As shown in plot 832, by applying a series of audible and subaudible tones with various cycle times 822 and measuring the change in Lref, it is possible to estimate the tympanic membrane displacement and extract frequency-dependent characteristics, such as the viscosity or elasticity of the fluid behind the tympanic membrane. For example, an exemplary elastometric measurement associated with a changing density or viscosity of a fluid may be the associated change in surface or membrane response time 874 with respect to a step change or phase delay 830 with respect to a sinusoidal frequency. Thus, the frequency domain response of a surface may be made by using a series of excitations 821 and measuring a series of surface responses 832.The reference path modulator 614 of FIGS. 6 and 7 or the mirror 114 of FIG. 3 may include a first path length modulator that centers the reference path length to include the tympanic membrane and a second path length modulator that rapidly varies the reference path length to provide adequate sampling of the axial movement of the tympanic membrane.

[0026] While Figure 8A shows a sinusoidal excitation that can be applied in a series of such excitations to generate a phase versus frequency response plot of surface displacement from a series of measurements, Figure 8B shows the time-domain step response equivalent of Figure 8A, in which a 50 daPa peak surface step pressure excitation 862 is applied to the tympanic membrane, which generates a measured tympanic membrane displacement sequence 872. Similarly, it is also possible to characterize the surface response based on the time delay 874 and amplitude response (shown as 0.5 mm) for the displacement response plot 872.

[0027] In one embodiment of the invention, a separate low-coherence optical source 102 or 602, such as an infrared range source, is used for increased depth penetration, and a separate visible source (not shown) is used coaxially to indicate the region of the tympanic membrane being characterized while pointing the measurement optical path on the tympanic membrane. The optical source 102 or 602 may be an infrared source, which reduces scattering and thereby provides additional depth of penetration. In another embodiment of the invention, the low-coherence optical source 102 or 602 is a visible optical source, thereby providing both illumination of the tympanic membrane region of interest and also measurement of tympanic membrane displacement, as described above.

[0028] This example is provided to provide an understanding of the invention, and it should be understood that the invention may be practiced in a variety of different ways, using different types of waveguides for propagating optical energy, and different optical sources, optical detectors, and methods of modulating the reference path length Lref. The scope of the invention is set forth in the claims that follow.

Claims

1. 1. A method performed by a system for characterization of fluid adjacent to a tympanic membrane, the system comprising a source of air pressure, a first splitter, a second splitter, a detector, and a controller, the method comprising: (a) the source of air pressure directs a time-modulated air pressure to the tympanic membrane and fluid adjacent to the tympanic membrane, the modulated air pressure being directed to the tympanic membrane and the fluid adjacent to the tympanic membrane without sealing an ear canal leading to the tympanic membrane; (b) the first splitter directs first low-coherence optical energy along a measurement path, the measurement path intersecting the tympanic membrane, and the first low-coherence optical energy interacting with the tympanic membrane and the fluid adjacent to the tympanic membrane; and (c) the first splitter directing second low-coherence optical energy along a reference path; and (d) the second splitter combining the first low coherence optical energy and the second low coherence optical energy after the first low coherence optical energy interacts with the tympanic membrane and the fluid adjacent to the tympanic membrane and the first and second low coherence optical energies traverse the measurement and reference paths, respectively; (e) the second splitter directing the combined first and second low-coherence optical energies to the detector; and (f) the detector generating a detector output based on the combined first and second low-coherence optical energies; and (g) the controller determining at least one of an elasticity or a viscosity of the fluid adjacent the tympanic membrane based on the detector output and the modulated air pressure; A method comprising:

2. 10. The method of claim 1, wherein the determination of the elasticity or the viscosity of the fluid adjacent the tympanic membrane is based on at least one of a pedestal of the detector output or a reflected wavelength profile of the detector output.

3. The method of claim 1 , wherein the detector output comprises a wavelength-dependent response.

4. The method of claim 3, further comprising the controller comparing the wavelength-dependent response with a template response of at least one known material.

5. The method of claim 4 , wherein the template response comprises at least one of earwax, a healthy tympanic membrane, an inflamed tympanic membrane, bacterial fluid, exudate fluid, or adhesive fluid.

6. The method of claim 4, further comprising the controller indicating to a user the presence of at least one of earwax, a healthy tympanic membrane, an inflamed tympanic membrane, bacterial fluid, exudate fluid, or adhesive fluid based at least on the compared wavelength-dependent response to the template response.

7. The method of claim 1 , wherein the modulated air pressure comprises a periodic excitation of air pressure.

8. The method of claim 1 , wherein the modulated air pressure comprises an impulse excitation of air pressure.

9. The method of claim 7, wherein the frequency of the periodic excitation is in the range of 20 Hz to 20 kHz.

10. The method of claim 1, wherein the system further comprises a path length modulator, the path length modulator being (i) a voltage or current controlled actuator coupled to a mirror or (ii) a piezoelectric actuator optically coupled to the reference path or the measurement path, and the method further comprises the path length modulator modulating the length of the reference path or the length of the measurement path.

11. The method of claim 10 , wherein the length of the reference path is modulated by a first length or a second length, the first length being longer than the second length.

12. The method of claim 1 , wherein the source of air pressure includes a voice coil actuator.

13. The method of claim 1 , wherein the first low-coherence source or the second low-coherence source comprises a broadband light emitting diode, an infrared source, or a visible source.

14. The method of claim 1 , wherein the second splitter is optically coupled to the detector.

15. The method of claim 1 , wherein the measurement path, the reference path, or a combination thereof is provided as a free-space optical path.

16. The method of claim 1 , wherein the measurement path, the reference path, or a combination thereof is provided as a waveguide optical path.

17. The method of claim 1 , wherein the modulated air pressure comprises a plurality of air pressure modulation frequencies.

18. The method of claim 1 , wherein the detector output indicates a position of the eardrum.

19. 20. The method of claim 18, wherein at least one of the elasticity or the viscosity of the fluid adjacent the tympanic membrane is determined from a delay between the position of the tympanic membrane and a directed pressure of the modulated air pressure over time.

20. 20. The method of claim 18, wherein at least one of the elasticity or the viscosity of the fluid adjacent the tympanic membrane is determined from a peak pressure of the modulated air pressure and a peak change in amplitude of the position of the tympanic membrane over time.

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