John Peacock

Magnetically driven middle ear ossicles with laser vibrometry as a new diagnostic tool to quantify ossicular fixation.

Abstract Conclusion: Information on the degree of incus fixation can be gathered by measuring the ratio of incus to umbo long process velocity through the ear canal. Objectives: To test a new method of quantifying partial ossicular fixation in an ear with an elevated tympanic membrane. Methods: Measurements were made on four fresh-frozen human temporal bones. After elevating the tympanic membrane a small magnet was attached to the manubrium and an electromagnetic excitation coil was used to vibrate the ossicles. The vibration response of the tip of the incus long process and the umbo were measured before and after artificially fixating the incus to the lateral attic wall. Results: Partial incus fixation resulted in a decrease in both the incus and umbo velocities, with the incus velocity being more severely reduced. The decreased ratio of their vibrations is a clear indicator of the degree of incus fixation.

Measurement of the vibration of the middle ear ossicles with removed eardrum: A method for quantification of ossicular fixation

Chronic inflammation of the middle ear is a common disease in which the mobility of the middle ear ossicles may be reduced; resulting in hearing impairment. Knowledge of the degree of ossicular mobility is useful in helping a surgeon determine how to proceed with treatment. In advanced cases, mobility can be assessed by manually pressing on the ossicles, but in less advanced cases manual assessment can provide limited useful information. Ossicular vibration can be measured with a laser vibrometer, but only the manubrium of the malleus is optically visible without removing the eardrum. Since the eardrum is the means by which acoustic energy is translated into the mechanical motion of the ossicles, removing it renders any subsequent measurements of ossicular motion meaningless. We therefore devised a technique in which the ossicles are vibrated magnetically. After measuring the response of the umbo to acoustic stimulation, we removed the eardrum and attached a small magnet to the manubrium. An electromagnetic excitation coil was then used to vibrate the magnet, and the signal to the coil was adjusted until the vibration of the ossicles matches that achieved acoustically. In this paper we explain the method and describe some test measurements on a vinyl membrane, and some preliminary results obtained on a fresh-frozen human temporal bone before and after artificial fixation of the ossicles.

Towards quantitative diagnosis of ossicular fixation: Measurement of stapes fixations using magnetically driven ossicles in human temporal bones

Abstract Conclusion: Information on the degree of stapes fixation can be found by measuring the ratio of stapes to umbo and stapes to incus velocity. Objectives: To evaluate a method of quantifying ossicular fixation in an ear with elevated tympanic membrane. Method: Measurements were made on four fresh-frozen human temporal bones. After elevating the tympanic membrane, a small magnet was attached to the manubrium and an electromagnetic excitation coil was used to vibrate the ossicles. The vibration response of the umbo, the tip of the incus long process, and the posterior crus of the stapes were measured before and after partially fixing the footplate with luting cement. Results: The velocities at the different measurement points were unequally affected by the fixation. The difference in the velocity ratio between different points provides an indication of the degree of footplate fixation.

Intraoperative assessment of ossicular fixation

Determining the degree of ossicular fixation is a difficult task, with the final assessment often being made with manual palpation during exploratory tympanotomy. A more objective method to evaluate ossicular fixation would be valuable. In this paper we describe a new method which makes use of a magnet and coil to measure ossicular motion through the ear canal with an elevated tympanic membrane. We report measurements of the vibration response at the umbo, the tip of the incus long process and the lateral posterior crus of the stapes before and after artificially fixing the stapes footplate and anterior mallear ligament with luting cement. Results were obtained on temporal bones, but the practicality of the method allows easy clinical implementation. Velocity ratios between different measurement points along the ossicular chain may provide a quantitative indication of the degree of stapes fixation. Isolated anterior mallear ligament fixation was not distinguishable from the unfixed condition.

Magnetically driven middle ear ossicles for optical measurement of vibrations in an ear with opened tympanic membrane.

Vibrations of the middle ear ossicles are easily measured by means of laser vibrometry. However, laser vibrometry requires free visual access to the object under investigation, and acquiring free visual access to the ossicles through the ear canal requires the removal of the tympanic membrane (TM), with the result that the ossicles can no longer be stimulated acoustically. To overcome this, we devised a new setup in which the ossicles can be driven magnetically. After measuring the response of the TM to an acoustic signal, we then remove it and attach a small magnet to the exposed manubrium (a part of the most lateral auditory ossicle, the malleus, which is normally attached to the TM). An electromagnetic excitation coil is then used to drive the magnet, and the output to the coil adjusted until the vibration of the manubrium, as measured by the vibrometer, matches that measured in response to the acoustic signal. Such a setup may have uses in research on middle ear mechanics, such as the measurement of nonlinearities in their response, as well as applications in the diagnosis of middle ear conditions such as the fixation of the ossicles by otosclerosis or in chronic otitis media. We describe our setup and discuss the viability of our method and its future clinical potential by presenting some measurements on an artificially fixated ear.

Optical Measurements of Nonlinearity in the Middle Ear

The primary function of the middle ear is to bridge the acoustic impedance difference between air in the ear canal and the fluid of the cochlea. At audible frequencies and at sound pressures below about 96 dB SPL, this system is thought to behave linearly. However, measurements in gerbils have indicated that at higher sound pressure levels the system begins to show small nonlinearities, which increase with the pressure level [1]. Given that they have been measured in gerbils, the same behaviour can be expected in other mammals, including humans.

Laser Doppler velocimetry for measurement of nonlinearity in the vibrations of the middle ear

At audible Frequencies and at sound pressure below 96 dB SPL the mammalian middle ear is known to behave as an almost entirely linear system. However, as we go to higher sound pressure levels, smaller nonlinear distortions begin to appear, and increase with increasing pressure level. Some modern hearing aids seek to remedy hearing impairment by amplifying sounds to sound pressure levels as high as 130 or 140 dB SPL. Thus at these levels the small nonlinear distortions can become significant, and understanding their behaviour could help us to improve the design of these hearing aids. In order to measure the tiny vibration amplitudes of the middle ear, and to detect the even smaller nonlinear distortions, a very sensitive measurement and analysis method is needed. The tiny vibration amplitudes of the middle ear can easily be measured with laser vibrometry. Thanks to the highly linear response of LDV, the technique is also able to measure small nonlinearities. To detect the nonlinear distortions we developed...

Magnetically driven middle ear ossicles for optical measurement of vibrations in an ear with opened eardrum

Vibrations of the middle ear ossicles are easily measured by means of laser vibrometry. However, exposing the ossicles requires the removal of the eardrum, with the result that the ossicles can no longer be stimulated acoustically. To overcome this we devised a new set up in which the ossicles can be driven magnetically. After measuring the response of the eardrum to an acoustic signal, we then remove the eardrum and attach a small magnet to the exposed manubrium (the part of the first auditory ossicle, the malleus, which is normally attached to the eardrum). An electromagnetic excitation coil is then used to drive the magnet, and the output to the coil adjusted until the vibration of the manubrium, as measured by the vibrometer, matches that measured in response to the acoustic signal. Such a set-up has uses in research on middle ear mechanics, such as the measurement of non-linearities in their response, as well as applications in the diagnosis of middle ear conditions such as the fixation of the ossicl...

Laser vibrometry for measurement of nonlinear distortions in the vibration of weakly nonlinear slowly time-varying systems

Recently, a new signal analysis method was developed to detect small non-linear distortions in weakly non-linear systems using specially designed broadband excitation signals, i.e. odd random phase multisines. The method allows the detection and quantification of the system response, noise level and both odd and even degree nonlinear distortions over an extensive frequency range from one single short-term measurement. Here, this method is implemented in an opto-acoustical set-up to detect small non-linearities in the response of vibrating structures. Because of the highly linear response achievable with heterodyne vibrometry, it is possible to detect non-linearities in the system under test with extremely high sensitivity. Non-linear behaviour is very common in biomechanical systems, but their dynamics and thus response might change over time. This leads to measurement artifacts that cause an overestimation of the noise level. A correction algorithm can be applied to remove the effect of these time variations, so that heterodyne vibrometry also allows the detection and quantification of non-linearities in unstable biomechanical systems. In this paper the technique is demonstrated with a measurement of the non-linear distortions in the vibration of the gerbil middle ear, where the use of a non-contact optical detection method is essential to not disturb the tiny vibrating structures.