Abstract:
An acoustic reflectometry instrument and method for ascertaining fluid presence in an ear. Drive side normalization involves normalizing the speaker to adjust its output to compensate for non-linearity over a frequency range used for acoustic reflectometry measurement of the ear. The microphone is normalized to compensate for system non-linearity. Measurement involves repetition a selected number of times until the spectral gradient angle is within a specified range for each repetition to provide validation of the measurement. For enhanced reliability, various sources of error are tested.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    None. 
       FIELD OF THE INVENTION 
       [0002]    This invention relates generally to the field of acoustic reflectometry and deals more particularly with a method and apparatus making use of acoustic reflectometry for evaluation of the ear to detect the presence of fluid which may be an indication of Otitis Media. 
       BACKGROUND OF THE INVENTION 
       [0003]    Acoustic reflectometry is known to be useful in detecting the presence of fluid in the middle ear cavity. Excessive fluid levels may be an indication of Otitis Media or other afflictions. Acoustic reflectometry techniques typically involve propagating an audio signal at a number of frequencies through the ear canal. The reflected energy may be analyzed using known processes to determine the mechanical resonance characteristics of the ear drum. The shape of the frequency response curve is used to determine a spectral gradient angle which is a measurement of the characteristics of a null in the spectral curve. 
         [0004]    In healthy ears, the ear drum has ample freedom of motion because the middle ear cavity is not under pressure. Accordingly, the resonance curve is shallow and the spectral gradient angle has a low value. Conversely, when fluid is present in the middle ear space, it restricts the motion of the ear drum. Then, a sharp resonance curve results along with a high spectral gradient value. Thus, the spectral gradient angle can be used to diagnose the likely presence or absence of fluid in the middle ear cavity and the relative risk of Otitis Media. 
         [0005]    While instruments have been developed and used successfully based on acoustic reflectometry, they have not been wholly without problems. The relatively high cost of the instruments has been a notable disadvantage. In particular, expensive microphones and speakers have been required in order to provide acceptable levels of accuracy and reliability. Because of the need for costly components, it has been impractical to provide instruments that are inexpensive enough to be made available to ordinary consumers as opposed to medical professionals. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention is directed to an acoustic reflectometry instrument and method employing improved techniques to increase the accuracy and reliability of the measurements while allowing for relatively low cost components. 
         [0007]    In accordance with one aspect of the invention, drive side normalization is used to normalize the speaker such that its power level is substantially equal at all frequencies, thereby compensating for non-linearity of the frequency response. Accordingly, and when used with a normalization of the microphone and the calibration of the instrument, a lower cost is achieved because there is no need for a high cost speaker as has been required in the past. 
         [0008]    In accordance with another aspect of the invention, the accuracy of the measurement is enhanced by repeating each measurement a selected number of times and confirming that each repetition results in a spectral gradient angle which does not depart unduly from the other repetitions. A time limit to complete all repetitions may be imposed for even more rigorous validation of the measurements. Various sources of error may also be investigated to provide greater assurance that the measurements are valid, thereby enhancing the reliability and accuracy of the instrument. 
         [0009]    Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0010]    In the accompanying drawings, which form a part of the specification and are to be read in conjunction therewith and in which like reference numerals are used to indicate like or similar parts in the various views: 
           [0011]      FIG. 1  is a perspective view of an acoustic reflectometry instrument constructed according to a preferred embodiment of the present invention; 
           [0012]      FIG. 2  is a schematic diagram of the principal components of the acoustic reflectometry instrument of  FIG. 1 ; 
           [0013]      FIG. 3  is a block diagram illustrating a preferred normalization and calibration process that may be used in accordance with the invention; 
           [0014]      FIG. 4  is a flow chart of a preferred measurement process that may be used in accordance with the invention; and 
           [0015]      FIG. 5  is a flow chart of a preferred wake and sleep process conducted in accordance with the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    Referring now to the drawings in more detail and initially to  FIG. 1 , the present invention is directed to the use of acoustic reflectometry for evaluation and diagnosis of the ear. The invention may be implemented using an instrument which is generally identified by numeral  10  and which may be a handheld device having a handle  12 . The head end of the instrument  10  is provided with a tip  14  having a size and shape to be inserted into an ear that is to be diagnosed. The head of the instrument may also be provided with a panel  16  having various control components and displays which may include a number of LED indicators  18  and other indicators  20 . 
         [0017]      FIG. 2  depicts diagrammatically the principal components of the instrument  10 . A circuit board  22  within the enclosure or housing  24  of the instrument controls its operation using control software  26 . A scan switch  28  may be activated to initiate a measurement. A display  30  and beeper  32  or other audible device may be included and selectively activated by the control software  26 . A speaker  34  and microphone  36  are associated with an acoustic chamber  38  which connects with the tip  14 . The tip  14  may be optionally covered by a removable tip cover  40 . 
         [0018]    Power is supplied by conventional batteries  42  contained in a battery compartment  44  accessible through a door  46  on the housing  24 . A test port  48  is provided to allow access through the battery compartment  44  for testing and trouble shooting purposes. 
         [0019]    In accordance with the embodiment of the invention shown in  FIGS. 1 and 2 , incident sound waves from the speaker  34  are propagated through the acoustic chamber  38  and tip  14  into the ear canal to the tympanic membrane. The incident waves are propagated at a variety of frequencies in a frequency range that includes the resonant frequency of the tympanic membrane. Some of the incident waves are reflected back through the tip  14  and acoustic chamber  38  to the microphone  36  which obtains the vector sum of the incident and reflected waves. An acoustic reflective curve for the frequency spectrum is calculated, and the null value of the curve is determined. This allows for a measurement of the spectral gradient angle of the null of the spectral curve, providing a basis for determining the presence of fluid in the ear cavity and allowing diagnosis of one or more conditions of the ear (principally, the relative risk of Otitis Media). 
         [0020]    Instrument accuracy depends on the speaker  34  putting out substantially the same power level over the full range of frequencies that are propagated. The present invention provides for normalizing the drive levels so that each frequency outputs a sound pressure level equal to an average pressure level obtained over the frequency within a predetermined range. For example, known output pressure levels from a device known to be accurate may be obtained and averaged over the frequency range to be used. The speaker drive is thus set to compensate for the variance from what the speaker output should be ideally. This procedure may be referred to as drive side normalization. 
         [0021]    The drive side normalization is effected in block  50  in  FIG. 3 . The output is adjusted at each frequency to compensate for the nonlinear speaker response. By carrying out drive side normalization in this manner, a relatively inexpensive speaker can be used because the speaker is not required to provide a flat frequency response. With continued reference to  FIG. 3 , the normalization and calibration process includes microphone normalization in block  52  wherein the input is adjusted to compensate for the nonlinearity of the system response. In block  54 , a plurality of calibration tubes are used having known expected responses, and the actual responses of the tubes are obtained during the calibration process. In block  56 , the differences between the expected calibration tube responses and the actual responses are compared and used to construct a model which is stored as indicated at block  58 . The accuracy of the calibration is verified in block  60  by comparing readings of the calibration tubes indicated by the model with the known expected readings. 
         [0022]      FIG. 4  depicts in flow chart form the process the instrument I  0  uses to take measurements indicative of the health of the ear and to validate the measurements. 
         [0023]    First, a determination is made at block  62  as to the presence of ambient noise. If ambient noise is present, an error flag is set in block  64  before block  66  is entered. If there is no ambient noise, block  66  is entered directly from block  62 . In block  66 , an output “chirp” is generated by the speaker  34 . For example, the chirp may consist of a sequence of tones that are generated at each of 44 different frequencies within a selected frequency range (which may be from 1.8 kHz to 4.4 kHz. Eight cycles of each frequency (“ramp up” cycles) may be used to allow stabilization of the acoustic system before a measurement is made. Four cycles (“ramp down” cycles) may be used to reduce resonance. 
         [0024]    The sound pressure or intensity is measured using the microphone  36 . If there is no ADC saturation as determined in block  70 , block  72  is entered. If there is ADC saturation, block  74  is entered to set an error flag, and block  72  is then entered. If there is no scaling error detected in block  72 , block  76  is entered. If there is a scaling error, block  78  is entered to set an error flag before block  76  entered. If there is an absence of ambient noise as determined in block  76 , block  80  is entered. If ambient noise is detected, block  82  sets an error flag before block  80  is entered. From the measurements of the same pressures at each frequency (block  68 ), the sound pressure is plotted over the frequency range to provide a calculation of the spectral density in block  80 . Then, a determination is made in block  84  as to the detection of a valley. If there is a valley, the process moves to block  86 . In block  86 , the angle of the null in the spectral density plot is determined to provide the spectral gradient angle. The next step is carried out in block  88 . If a valley is not detected, block  86  is bypassed and block  88  is entered directly from block  84 . If it is determined in block  88  that the instrument is not properly in the ear, block  90  is entered to determine if there is a blockage. If there is not, block  92  is entered to determine if there is an error. In order to minimize the potential for error, a successful measurement requires four chirps to result in spectral gradient angles within a selected range and time (such as within + or −5° and within 10 seconds, for example), and also without error conditions present. If there is not a successful measurement satisfying these requirements, the process is repeated until there is a successful measurement. Thus, in block  94  a determination is made as to whether there has been expiration of a 10 second timeout period. If it is determined in block  88  that the instrument is not properly in the ear or if an error is detected in block  92 , block  96  is entered to set the angle to an error angle, and block  94  is then entered. 
         [0025]    If it is determined in block  94  that the 10 second timeout period has elapsed, block  96  is entered to display a “try again” status of the instrument, and then the process is ended in block  100 . If the 10 second timeout period has not expired, block  102  is entered from block  94  and a determination is made as to whether two good angles have been generated within 10°. If not, block  62  is entered from block  102  and the process is repeated. If two good angles within 10° are detected in block  102 , block  104  is entered and a display of the risk level associated with the detected angle is generated prior to ending the process in block  100 . 
         [0026]    Generally, lower spectral gradient angles indicate healthier ears and a lesser risk of Otitis Media. One aspect of the present invention contemplates that the risk of Otitis Media may be categorized into different levels depending on the spectral gradient angle. By way of example, five risk levels may be established, with a spectral gradient angle less than 49° falling into a low risk level of 5, angles equal to or greater than 49° and equal to or less than 59° falling into risk level 4, angels greater than 59° but less than or equal to 69° falling into risk level 3, angles greater than 69° but less than or equal to 89° falling into risk level 2, and angles greater than 89° falling into the highest risk level of one. For each successful measurement, the risk level (block  104 ) in accordance with the foregoing may be displayed on the panel  16 , as by energizing appropriate LEDs  18 . 
         [0027]      FIG. 5  depicts a wake and sleep process that may be included. When the instrument “wakes” from a sleeping condition in block  106 , block  108  is entered to determine if a check sum error has occurred. If it has, block  110  is entered and the instrument reverts to the sleep mode. If there is no check sum error, the battery level is checked in block  112  and a low battery indicator is set if the battery level is less than a predetermined value (2.6 volts, for example). If the battery is in an unduly low condition, block  110  is entered and the instrument reverts to the sleep mode. If the battery is not unduly low, block  116  is entered and the measurement and the validation process depicted in  FIG. 4  is carried out. Then, the battery level is again checked in block  118  and an indicator is set if the battery is unduly low. If the battery is unduly low as indicated in block  120 , block  110  is entered. If the battery is not unduly low, block  122  is entered and a performed scan determination is made. If the performed scan determination is negative, block  110  is entered. Conversely, if the performed scan determination is positive, block  116  is entered. 
         [0028]    The instrument  10  may have a variety of modes of operation and may provide a variety of output signals and indications. For example, there may be a standby mode in which all visual and audio indicators are inactive. A scan mode may be entered when the scan switch  28  is activated. In the scan mode, all of the LED indicators  18  may be briefly activated. Also, self-tests may be conducted. Failure of a self-test generates a fault condition and entry into the error mode. When the scan mode is entered, a beep or other audible sound may be generated by the beeper  32  or other audio device. If the battery condition is unduly low, one of the indicators  20  may be energized to display a low battery indication. If the self-tests are completed successfully in the scan mode, the measurement process is initiated. A short beep or other signal may be provided between each chirp. During the measurement process, the LEDs  18  may be energized one at a time in sequence, with one sequence occurring for each chirp. At the end of a successful measurement process, the complete mode may be entered. 
         [0029]    In the complete mode, a lengthy beep or other distinctive signal may be given to indicate a successful measurement. The Otitis Media risk level (1-5) may be displayed by energizing the LEDs  18  in a manner corresponding to the measured risk level. While the instrument is in the complete mode, the scan switch  28  may be activated to enter the scan mode again. After five seconds or some other selected time in the complete mode has elapsed without the scan switch having been activated, the instrument goes into the standby mode. 
         [0030]    A fault condition or error results in the instrument entering the error mode. Three beeps or some other signal may then be generated as an indication of the error. If the error is due to failure of the self-test, a device error may be signaled audibly or on the panel  16  visually. If the error is due to an unsuccessful measurement, a visual display on panel  16  or an audible or other signal may be provided to identify the cause of the error, and a try again indication may be displayed on panel  16 . When five seconds or some other selected time has elapsed, the instrument goes into the standby mode. 
         [0031]    While the tip  14  may be removable and replaceable, it may also be an integral part of the instrument  10 . In this case, removable tip covers such as the cover  40  may be provided so that after each use, the tip cover can be removed and replaced by an unused cover. 
         [0032]    From the foregoing it will be seen that this invention is one well adapted to attain all ends and objects hereinabove set forth together with the other advantages which are obvious and which are inherent to the structure. 
         [0033]    It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims. 
         [0034]    Since many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative, and not in a limiting sense.