System for in vivo measurements of tympanic membrane vibration
View Patent ↗A system for noninvasive in vivo functional imaging of the human ear and measurement of nanometer scale motion of the tympanic membrane under various acoustic excitations, and identification of vibration patterns that vary between human subjects in response to sound. By combining spectrally encoded imaging with phase-sensitive spectral-domain interferometry, high-resolution imaging of the membrane surface is obtained within a fraction of a second, through a handheld imaging probe. The detailed physiological data obtained allows measuring a wide range of clinically relevant parameters for patient diagnosis, and provides a new tool for studying middle and inner ear physiology. Use of a line measurement technique, without mechanically scanning the probe beam, enables characteristics of the membrane vibration to be measured, in a time scale of tenths of a second, thereby reducing the possibility of inaccuracy because of movements of the hand-held instrument.
1 . A system for determining the vibrational characteristics of a single line across a tympanic membrane of a subject, the system comprising:
a light source adapted to input into the system, a beam of the light having a range of wavelengths;
a diffracting element configured to spectrally disperse the beam of light along the single line;
a lens system configured to focus the single line of spectrally dispersed light through the auditory canal of a subject, such that it impinges on the tympanic membrane of the subject;
a control system adapted to determine from a spectrometric analysis of light resulting from the interference of the spectrally dispersed light reflected from the tympanic membrane with a reference beam, the vibrational amplitude of motion of the tympanic membrane as a function of position along the single line,
wherein the spectral dispersion of the beam of light along the single line enables the system to provide the vibrational characteristics of the single line across the tympanic membrane over a range of acoustic excitation frequencies, in a time sufficiently short that the accuracy of the measurement of the tympanic membrane vibrational motion is unaffected by in vivo environmental motions.
2 . The system according to claim 1 wherein the lens system is further configured to provide wide field imaging of the illuminated single line on the tympanic membrane.
3 . The system according to claim 2 further comprising a widefield camera adapted to enable operator guidance of the position of the single line of the beam of light across the tympanic membrane.
4 . The system according to claim 1 , further comprising a sound source positioned to apply an acoustic signal having the range of excitation frequencies to the tympanic membrane.
5 . The system according to claim 4 wherein the sound source is configured to output the acoustic signal amplitude modulated over a range of up to 0 to 90 dB, and where the acoustic frequencies are in a range of up to 0 to 20 KHz.
6 . The system according to claim 4 wherein the range of frequencies are obtained either by frequency modulation of the acoustic signal, or by application of a pulse of the acoustic signal, the pulse containing signals over the range of frequencies.
7 . The system according to claim 4 , wherein a frequency response of separate parts of the tympanic membrane along the single line can be determined.
8 . The system according to claim 1 , further comprising a mechanical scanning element configured to adjust a position of the single line of light on the membrane.
9 . The system according to claim 8 , wherein the controller is configured to input the position of the single line on the membrane, and to output a signal to align the scanning element, such that the single line of light maintains its position in spite of mutual motion between the system and the membrane.
10 . The system according to claim 9 , wherein the position of the line of light on the membrane is determined using image processing of a camera image of the membrane.
11 . The system according to claim 1 , wherein the diffracting element and lens system are disposed within an otoscope or an endoscope.
12 . The system according to claim 1 , wherein the light source has a predefined polarization, and paths along which the light passes essentially maintain the polarization of the light passing therethrough.
13 . The system according to claim 1 , wherein the light source comprises a swept wavelength source, such that the diffracting element temporally disperses a spot of light along the line, the spot having varying wavelength according to time varying wavelengths of the swept source.
14 . The system according to claim 8 , wherein the mechanical scanning element is controlled to align the single line of light such that it includes at least one of the umbo region and the malleus region.
15 . A method of reducing the time required to determine the vibrational characteristics of a single line across a tympanic membrane of a subject, the method comprising:
applying an acoustic excitation to the ear of the subject from a sound source;
inputting a beam of the light having a range of wavelengths into the ear of the subject;
spectrally dispersing the beam of light using a diffracting element, such that it forms the single line across the tympanic membrane;
focusing the single line of spectrally dispersed light with a lens system through the auditory canal of the subject, such that it impinges on the tympanic membrane of the subject; and
determining from a spectrometric analysis of light resulting from the interference of the spectrally dispersed light reflected from the tympanic membrane with a reference beam, the vibrational amplitude and relative phase of motion of the tympanic membrane as a function of position along the single line,
wherein the spectral dispersion of the beam of light along the single line enables a reduction of the time taken for a measurement of vibrational characteristics of any point along the single line on the tympanic membrane over a range of acoustic excitation frequencies, such that the measurement of the tympanic membrane vibrational motion over the range of acoustic excitation frequencies, can be performed within a time such that the measurement is less affected by in vivo motion artifacts.
16 . The method according to claim 15 , further comprising the steps of using the lens system to provide wide field imaging of the illuminated single line on the tympanic membrane, and of using a wide field camera to enable an operator to guide the position of the single line of the beam of light across the tympanic membrane.
17 . The method according to claim 15 , wherein the sound source is configured to modulate the acoustic signal amplitude over a range of up to 0 to 90 dB, and to contain frequencies in a range of up to 0 to 20 KHz.
18 . The method according to claim 15 , wherein the range of acoustic excitation frequencies are obtained either by frequency modulation of the acoustic signal, or by application of a pulse of the acoustic signal, the pulse containing signals over the range of frequencies.
19 . The method according to claim 15 , further comprising the step of determining the frequency response of separate parts of the tympanic membrane along the single line.
20 . The system according to claim 1 , where the range of acoustic excitation frequencies is a swept range of frequencies.
21 . The method according to claim 15 , wherein the range of acoustic excitation frequencies is a swept range of frequencies.