Chia-Fone Lee

Three‐Dimensional Reconstruction and Modeling of Middle Ear Biomechanics by High‐Resolution Computed Tomography and Finite Element Analysis

Objective: To present a systematic and practical approach that uses high‐resolution computed tomography to derive models of the middle ear for finite element analysis.

Optimal Graft Thickness for Different Sizes of Tympanic Membrane Perforation in Cartilage Myringoplasty: A Finite Element Analysis†

Objective: The purpose of this study was to determine, using finite element analysis, the optimal graft thickness for cartilage myringoplasty in patients with different sizes of tympanic membrane (TM) perforations.

A novel opto-electromagnetic actuator coupled to the tympanic membrane

A new type of electromagnetic vibration transducer designed to be placed onto the tympanic membrane was developed. The actuator consisted of two photodiodes, two permanent magnets, an aluminum ring, two opposing wound coils, a latex membrane and a Provil Novo membrane. An optic probe was designed to allow sound and light signals to enter the ear canal, thereby preventing the acoustic occlusion effect of traditional ear molds. Two light-emitting diodes were used for carrying the input signals. The corresponding photodiodes were used for receiving the light signals and generating currents in the actuator. The opto-electromagnetic vibration actuator was fabricated and tested using a Laser Doppler vibrometer. The actuator showed displacements of vibration between 30 and 1 nm from 300 to 6500Hz and reduced in amplitude at higher frequencies. The average gain of the actuator with 140microA on the umbo displacement was about 20 dB relative to 87 dBA at the distance of 6cm from the tympanic membrane and 0microA in actuator.

COMPUTER AIDED THREE-DIMENSIONAL RECONSTRUCTION AND MODELING OF MIDDLE EAR BIOMECHANICS BY HIGH-RESOLUTION COMPUTED TOMOGRAPHY AND FINITE ELEMENT ANALYSIS

In order to present a systematic and practical approach that uses high-resolution computed tomography (HRCT) to derive models of the middle ear for finite element analysis (FEA). This prospective study included 31 subjects with normal hearing and no previous otological disorders. Temporal bone images obtained from 15 right ears and 16 left ears were used for evaluation and reconstruction. High-resolution computed tomography of temporal bone was performed using simultaneous acquisition of 16 sections with a collimated slice thickness of 0.625 mm. All images were transferred to an Amira visualization system for 3D reconstruction. The created 3-D model was translated into two commercial modeling packages, Patran and ANSYS, for finite element analysis. The characteristic dimensions of the model were measured and compared with previous published histological section data. This result confirms that the geometric model created by the proposed method is accurate except the tympanic membrane is thicker than that of histological section method. No obvious difference in the geometrical dimension between right and left ossicles was found (p > 0.05). The 3D model created by finite element method and predicted umbo and stapes displacements are close to the bounds of the experimental curves of Nishiharas, Hubers, and Gans data across the frequency range of 100-8000 Hz. The model includes a description of the geometry of the middle ear components, and dynamic equations of vibration. The proposed method is quick, practical, low cost and most importantly, non-invasive as compared with histological section methods.

Computer aided modeling of human mastoid cavity biomechanics using finite element analysis

The aim of the present study was to analyze the human mastoid cavity on sound transmission using finite element method. Pressure distributions in the external ear canal and middle ear cavity at different frequencies were demonstrated. Our results showed that, first, blocking the aditus improves middle ear sound transmission in the 1500- to 2500-Hz range and decreases displacement in frequencies below 1000 Hz when compared with the normal ear. Second, at frequencies lower than 1000 Hz, the acoustic pressures were almost uniformly distributed in the external ear canal and middle ear cavity. At high frequencies, higher than 1000 Hz, the pressure distribution varied along the external ear canal and middle ear cavity. Third, opening the aditus, the pressures difference in dB between the middle ear cavity and external ear canal were larger than those of the closed mastoid cavity in low frequency (<1000 Hz). Finally, there was no significant difference in the acoustic pressure between the oval window and round window is noted and increased by 5 dB by blocking the aditus. These results suggest that our complete FE model including the mastoid cavity is potentially useful and can provide more information in the study of middle ear biomechanics.

Biomechanical Modeling and Design Optimization of Cartilage Myringoplasty Using Finite Element Analysis

The purpose of this study was to determine the acoustic transfer characteristics of cartilage for optimal cartilage myringoplasty. In order to do so, we developed a cartilage plate/tympanic membrane-coupled model using finite element analysis. Cartilage specimens of the tragus were obtained from fresh human cadavers, and the parameters of the tragus were determined by curve fitting and cross-calibration. A cartilage plate was used to repair an eardrum perforation, and the new coupled tympanic membrane-cartilage complex was loaded into our 3-dimensional biomechanical model of the middle ear for analysis. Our results show that first the β-damping value of the cartilage plate depends on frequency. The value of β damping was close to 3 × 10–4 s at lower frequencies and 5 × 10–6 s at higher frequencies. Secondly, reducing cartilage thickness leads to an improvement of its acoustic transfer qualities. From an acoustics point of view, the 0.1- to 0.2-mm cartilage plate seems to be most preferable with regard to tympanic membrane vibration. Furthermore, thicknesses of 0.2 mm at lower frequencies and 0.1 mm at higher frequencies were regarded as good compromises between sufficient mechanical stability and low acoustic transfer loss.

Virtual biopsy of rat tympanic membrane using higher harmonic generation microscopy

Multiharmonic optical microscopy has been widely applied in biomedical research due to its unique capability to perform noninvasive studies of biomaterials. In this study, virtual biopsy based on back-propagating multiple optical harmonics, combining second and third harmonics, is applied in unfixed rat tympanic membrane. We show that third harmonic generation can provide morphologic information on the epithelial layers of rat tympanic membrane as well as radial collagen fibers in middle fibrous layers, and that second harmonic generation can provide information on both radial and circular collagen fibers in middle fibrous layers. Through third harmonic generation, the capillary and red blood cells in the middle fibrous layer are also noted. Additionally, the 3-D relationship to adjacent bony structures and spatial variations in thickness and curvature are obtained. Our study demonstrates the feasibility of using a noninvasive optical imaging system for comprehensive evaluation of the tympanic membrane.

THE OPTIMAL MAGNETIC FORCE FOR A NOVEL ACTUATOR COUPLED TO THE TYMPANIC MEMBRANE: A FINITE ELEMENT ANALYSIS

A new type of electromagnetic vibration transducer designed to be placed onto the tympanic membrane will be developed. Such an electromagnetic transducer should have the following characteristics: small in size, high-energy efficiency and suitable frequency bandwidth. In order to find out the optimal electromagnetic force and to predict the frequency-amplitude characteristics, a finite element middle ear biomechanical model was used to derive the optimal magnetic force of the actuator in this study. First, the electromagnetic transducer coupled to the ear drum was created by using a computer-aided design (CAD). Then the new coupled tympanic membrane-transducer complex was loaded to a 3-dimensional biomechanical model in the middle. The air gap between magnet and coil, input current and vibration force were calculated by finite element analysis simulation. In addition, gain and frequency response curves of the actuator were also calculated. Predicted displacement of tip of the malleus induced by the sound pressure of 80 dB SPL with different input currents are computed from the finite element model over the auditory frequency range of 100–8000 Hz as the force input into the ANSYS software. Simulated results show displacements of vibration are about 100 nm in the range from 100–1000 Hz and reduced when the frequencies are higher than 1000 Hz. Functional gains were about 20–25 dB across the 100 to 8,000 Hz frequency range.

Design Optimization of Cartilage Myringoplasty using Finite Element Analysis

Objective: The purpose of this study was to determine the acoustic transfer characteristics of cartilage for optimal cartilage myringoplasty. Material and Methods: We developed a cartilage plate-tympanic membrane coupled finite element model to investigate the transfer characteristics of cartilage myringoplasty. Cartilage specimens of the tragus were obtained from fresh human cadavers and were investigated by means of a tympanic membrane model. The parameters of tragus were determined by curve fitting and cross calibration. The cartilage plate was reconstructed based on an ear drum perforation using our 3-dimensional middle ear biomechanical model. The optimal thickness of cartilage myringoplasty was calculated using finite element analysis. Result: Reducing cartilage thickness leads to an improvement into acoustic transfer qualities. From an acoustic point of view, 0.1-0.2 mm thick cartilage plate seems to give the best results in term of tympanic membrane vibration. Conclusion: Tragal cartilage is useful for reconstruction of tympanic membrane from the perspective of acoustic properties. The acoustic transfer loss by the cartilage can be reduced by decreasing its thickness. A thickness of 0.2 mm at lower frequency and 0.1mm at higher frequency are regarded as a good compromise between sufficient mechanical stability and low acoustic transfer loss.

A Novel Aerosol-Mediated Drug Delivery System for Inner Ear Therapy: Intratympanic Aerosol Methylprednisolone Can Attenuate Acoustic Trauma

We developed a novel aerosol-mediated drug delivery system for inner ear therapy by using a silicon-based multiple-Fourier horn nozzle. Intratympanic aerosol (ITA) methylprednisolone (MP) delivery can protect hearing after acoustic trauma. The highest concentration of MP (38.9 ± 5.47 ppm) appeared at 2 h and declined rapidly within 10 h. The concentrations of MP remained at a relatively low level for more than 10 h. Compared to the baseline, the auditory brainstem response (ABR) thresholds shifted markedly at 1 h after noise exposure in all groups (p <; 0.05). From the cochleograms, it can be noted that the main lesions encompassed the 2-20 kHz frequency range. Significant differences ( ) were observed for the range between 5 and 8 kHz in the cell loss of outer hair cells (OHCs). The losses for IHCs were lower than for OHCs. The MP movement in the middle ear was simulated by a convection diffusion equation with a relaxation time. The relaxation time was 0.5 h, and the concentration threshold of MP on the round window membrane (RWM) in the middle ear (C T) was 8900 ppm. Using the unit hydrograph (UH) method, we obtained a proper boundary concentration on the RWM at the cochlea, which resulted in a well-fit concentration. Finally, a linking mechanism between the middle ear and the cochlea was established by the RWM. The adjustable permeability and concentration threshold provide the flexibility to match the peak times and peak values of the concentration on the RWM in the middle ear and the cochlea.