María del Socorro Hernández-Montes

Motion of the surface of the human tympanic membrane measured with stroboscopic holography

Sound-induced motion of the surface of the human tympanic membrane (TM) was studied by stroboscopic holographic interferometery, which measures the amplitude and phase of the displacement at each of about 40,000 points on the surface of the TM. Measurements were made with tonal stimuli of 0.5, 1, 4 and 8 kHz. The magnitude and phase of the sinusoidal displacement of the TM at each driven frequency were derived from the fundamental Fourier component of the raw displacement data computed from stroboscopic holograms of the TM recorded at eight stimulus phases. The correlation between the Fourier estimates and measured motion data was generally above 0.9 over the entire TM surface. We used three data presentations: (i) plots of the phasic displacements along a single chord across the surface of the TM, (ii) phasic surface maps of the displacement of the entire TM surface, and (iii) plots of the Fourier derived amplitude and phase-angle of the surface displacement along four diameter lines that define and bisect each of the four quadrants of the TM. These displays led to some common conclusions: at 0.5 and 1kHz, the entire TM moved roughly in-phase with some small phase delay apparent between local areas of maximal displacement in the posterior half of the TM. At 4 and 8 kHz, the motion of the TM became more complicated with multiple local displacement maxima arranged in rings around the manubrium. The displacements at most of these maxima were roughly in-phase, while some moved out-of-phase. Superposed on this in- and out-of-phase behavior were significant cyclic variations in-phase with location of less than 0.2 cycles or occasionally rapid half-cycle step-like changes in-phase. The high frequency displacement amplitude and phase maps discovered in this study can not be explained by any single wave motion, but are consistent with a combination of low and higher order modal motions plus some small traveling-wave-like components. The observations of the dynamics of TM surface motion from this study will help us better understand the sound-receiving function of the TM and how it couples sound to the ossicular chain and inner ear.

Computer-assisted time-averaged holograms of the motion of the surface of the mammalian tympanic membrane with sound stimuli of 0.4–25 kHz

Time-averaged holograms describing the sound-induced motion of the tympanic membrane (TM) in cadaveric preparations from three mammalian species and one live ear were measured using opto-electronic holography. This technique allows rapid measurements of the magnitude of motion of the tympanic membrane surface at frequencies as high as 25 kHz. The holograms measured in response to low and middle-frequency sound stimuli are similar to previously reported time-averaged holograms. However, at higher frequencies (f>4 kHz), our holograms reveal unique TM surface displacement patterns that consist of highly-ordered arrangements of multiple local displacement magnitude maxima, each of which is surrounded by nodal areas of low displacement magnitude. These patterns are similar to modal patterns (two-dimensional standing waves) produced by either the interaction of surface waves traveling in multiple directions or the uniform stimulation of modes of motion that are determined by the structural properties and boundary conditions of the TM. From the ratio of the displacement magnitude peaks to nodal valleys in these apparent surface waves, we estimate a Standing Wave Ratio of at least 4 that is consistent with energy reflection coefficients at the TM boundaries of at least 0.35. It is also consistent with small losses within the uniformly stimulated modal surface waves. We also estimate possible TM surface wave speeds that vary with frequency and species from 20 to 65 m/s, consistent with other estimates in the literature. The presence of standing wave or modal phenomena has previously been intuited from measurements of TM function, but is ignored in some models of tympanic membrane function. Whether these standing waves result either from the interactions of multiple surface waves that travel along the membrane, or by uniformly excited modal displacement patterns of the entire TM surface is still to be determined.

Optoelectronic holographic otoscope for measurement of nano-displacements in tympanic membranes

Current methodologies for characterizing tympanic membrane (TM) motion are usually limited to either average acoustic estimates (admittance or reflectance) or single-point mobility measurements, neither of which suffices to characterize the detailed mechanical response of the TM to sound. Furthermore, while acoustic and single-point measurements may aid in diagnosing some middle-ear disorders, they are not always useful. Measurements of the motion of the entire TM surface can provide more information than these other techniques and may be superior for diagnosing pathology. We present advances in our development of a new compact optoelectronic holographic otoscope (OEHO) system for full field-of-view characterization of nanometer-scale sound-induced displacements of the TM surface at video rates. The OEHO system consists of a fiber optic subsystem, a compact otoscope head, and a high-speed image processing computer with advanced software for recording and processing holographic images coupled to a computer-controlled sound-stimulation and recording system. A prototype OEHO system is in use in a medical research environment to address basic science questions regarding TM function. The prototype provides real-time observation of sound-induced TM displacement patterns over a broad frequency range. Representative time-averaged and stroboscopic holographic interferometry results in animals and human cadaver samples are shown, and their potential utility is discussed.

Tympanic membrane contour measurement with two source positions in digital holographic interferometry

The data acquisition from the shape of an object is a must to complete its quantitative displacement measurement analysis. Over the past years whole field of view optical non-invasive testing has been widely used in many areas, from industrial ones to, for instance, biomedical research topics. To measure the surface contour from the tympanic membrane (TM) of ex-vivo cats digital holographic interferometry (DHI) is used in combination with a two-illumination positions method: the shape is directly measured from the phase change between two source positions by means of a digital Fourier transform method. The TM shape data in conjunction with its displacement data renders a complete and accurate description of the TM deformation, a feature that no doubt will serve to better comprehend the hearing process. Acquiring knowledge from the tissue shape indicates a mechanical behavior and, indirectly, an alteration in the physiological structure due to middle ear diseases or damages in the tissue that can deteriorate sound transmission. The TM shape contour was successfully measured by using two source positions within DHI showing that the TM has a conical shape. Its maximum depth was found to be 2 mm, considering the umbo as the reference point with respect to the TM annulus plane, where the setup is arranged in such a manner that it is capable of measuring a height of up to 7 mm.

Middle Ear Mechanics of Cartilage Tympanoplasty Evaluated by Laser Holography and Vibrometry

Goals: To assess the effects of thickness and position of cartilage used to reconstruct the tympanic membrane (TM) using a novel technique, time-averaged laser holography. Background: Cartilage is commonly used in TM reconstruction to prevent formation of retraction pockets. The thickness, position, and shape of the cartilage graft may adversely affect TM motion and hearing. We sought to systematically investigate these parameters in an experimental setting. Methods: Computer-assisted optoelectronic laser holography was used in 4 human cadaveric temporal bones to study sound-induced TM motion for 500 Hz to 8 kHz. Stapes velocity was measured with a laser Doppler vibrometer. Baseline (control) measurements were made with the TM intact. Measurements were repeated after a 0.5- or 1.0-mm-thick oval piece of conchal cartilage was placed on the medial TM surface in the posterior-superior quadrant. The cartilage was rotated so that it was either in contact with the bony tympanic rim and manubrium or not. Results: At frequencies less than 4 kHz, the cartilage graft had only minor effects on the overall TM fringe patterns. The different conditions had no effects on stapes velocity. Greater than 4 kHz, TM motion was reduced over the grafted TM, both with 0.5- and 1.0-mm-thick grafts. No significant differences in stapes velocity were seen with the 2 different thicknesses of cartilage compared with control. Conclusion: Computer-assisted optoelectronic laser holography is a promising technique to investigate middle ear mechanics after tympanoplasty. Such positioning may prevent postoperative TM retraction. These findings and conclusions apply to cartilage placed in the posterior-superior TM quadrant.

Finding the position of tumor inhomogeneities in a gel-like model of a human breast using 3-D pulsed digital holography.

3-D pulsed digital holography is a noninvasive optical method used to measure the depth position of breast tumor tissue immersed in a semisolid gel model. A master gel without inhomogeneities is set to resonate at an 810 Hz frequency; then, an identically prepared gel with an inhomogeneity is interrogated with the same resonant frequency in the original setup. Comparatively, and using only an out-of-plane sensitive setup, gel surface displacement can be measured, evidencing an internal inhomogeneity. However, the depth position cannot be measured accurately, since the out-of-plane component has the contribution of in-plane surface displacements. With the information gathered, three sensitivity vectors can be obtained to separate contributions from x, y, and z vibration displacement components, individual displacement maps for the three orthogonal axes can be built, and the inhomogeneitys depth position can be accurately measured. Then, the displacement normal to the gel surface is used to find the depth profile and its cross section. Results from the optical data obtained are compared and correlated to the inhomogeneitys physically measured position. Depth position is found with an error smaller than 1%. The inhomogeneity and its position within the gel can be accurately found, making the method a promising noninvasive alternative to study mammary tumors.

Displacement measurements over a square meter area using digital holographic interferometry

Abstract. Current industrial demand for optical nondestructive testing includes the displacement analysis of large object areas. This paper reports on the use of a digital holographic interferometer to measure displacements over an area of 1.14  m2. The object under study is a framed working table covered with a Formica layer fixed to a granite bench, and it is observed and illuminated employing a high speed and high resolution camera and a continuous wave high output power laser, respectively. A stabilization procedure needs to be established as long illumination distances are required in order to retrieve the entire surface optical phase during a series of continuous deformations. As a proof of principle, two different tests are presented: the first involves a slow continuous loading process and the second a vibration condition. The wrapped phase and displacement maps are both displayed.

Detection of biological tissue in gels using pulsed digital holography.

An out of plane optical sensitive configuration for pulsed digital holography was used to detect biological tissue inside solid organic materials like gels. A loud speaker and a shaker were employed to produce a mechanical wave that propagates through the gel in such a way that it generates vibrational resonant modes and transient events on the gel surface. Gel surface micro displacements were observed between the firing of two laser pulses, both for a steady resonant mode and for different times during the transient event. The biological tissue sample inserted approximately 2 cm inside the gel diffracts the original mechanical wave and changes the resonant mode pattern or the transient wave on the gel surface. This fact is used to quantitatively measure the gel surface micro displacement. Comparison of phase unwrapped patterns, with and without tissue inside the gel, allows the rapid identification of the existence of tissue inside the gel. The results for the resonant and transient conditions show that the method may be reliably used to study, compare and distinguish data from inside homogeneous and in-homogeneous solid organic materials.

Quantitative comparison of tympanic membrane displacements using two optical methods to recover the optical phase

Abstract The study and quantification of the tympanic membrane (TM) displacements add important information to advance the knowledge about the hearing process. A comparative statistical analysis between two commonly used demodulation methods employed to recover the optical phase in digital holographic interferometry, namely the fast Fourier transform and phase-shifting interferometry, is presented as applied to study thin tissues such as the TM. The resulting experimental TM surface displacement data are used to contrast both methods through the analysis of variance and F tests. Data are gathered when the TMs are excited with continuous sound stimuli at levels 86, 89 and 93 dB SPL for the frequencies of 800, 1300 and 2500 Hz under the same experimental conditions. The statistical analysis shows repeatability in z-direction displacements with a standard deviation of 0.086, 0.098 and 0.080 μm using the Fourier method, and 0.080, 0.104 and 0.055 μm with the phase-shifting method at a 95% confidence level for all frequencies. The precision and accuracy are evaluated by means of the coefficient of variation; the results with the Fourier method are 0.06143, 0.06125, 0.06154 and 0.06154, 0.06118, 0.06111 with phase-shifting. The relative error between both methods is 7.143, 6.250 and 30.769%. On comparing the measured displacements, the results indicate that there is no statistically significant difference between both methods for frequencies at 800 and 1300 Hz; however, errors and other statistics increase at 2500 Hz.

Preliminary results of tympanic membrane displacements using non-invasive optical methods

Quantitative analyses of the tympanic membrane mechanical properties are needed for better understanding of its role in detailed clinical evaluation. Optical methods like Digital Holographic Interferometry (DHI), time averaged holography and ESPI are quite promising for the investigation of biological tissues. Their demonstrated ability to detect displacement changes in quasi and real time and without contacting the sample surface under study provides relevant features, such as clinical and mechanical properties. In this research time averaged vibrations patterns are shown for fresh tympanic membrane specimens taken from post-mortem cats, and subject to acoustic stimuli in the frequency range of 485 Hz up to 10 kHz. The results may provide information about sample mechanical characteristics such as its elasticity coefficient. An important feature of this approach over other techniques previously used to study the vibrations of the tympanic membrane is that it only requires an image and less equipment to carry out the measurements. Good agreement was found between the present and past measurements from previous research work. Results show the usefulness of the method in the medical field in providing relevant data about key mechanical characteristics of biological samples.Quantitative analyses of the tympanic membrane mechanical properties are needed for better understanding of its role in detailed clinical evaluation. Optical methods like Digital Holographic Interferometry (DHI), time averaged holography and ESPI are quite promising for the investigation of biological tissues. Their demonstrated ability to detect displacement changes in quasi and real time and without contacting the sample surface under study provides relevant features, such as clinical and mechanical properties. In this research time averaged vibrations patterns are shown for fresh tympanic membrane specimens taken from post-mortem cats, and subject to acoustic stimuli in the frequency range of 485 Hz up to 10 kHz. The results may provide information about sample mechanical characteristics such as its elasticity coefficient. An important feature of this approach over other techniques previously used to study the vibrations of the tympanic membrane is that it only requires an image and less equipment to carry out the measurements. Good agreement was found between the present and past measurements from previous research work. Results show the usefulness of the method in the medical field in providing relevant data about key mechanical characteristics of biological samples.