Home Medicine Doppler optical coherence tomography as a promising tool for detecting fluid in the human middle ear
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Doppler optical coherence tomography as a promising tool for detecting fluid in the human middle ear

  • Lars Kirsten EMAIL logo , Simon Baumgärtner , Mikael Timo Erkkilä , Jonas Golde , Max Kemper , Thomas Stoppe , Matthias Bornitz , Marcus Neudert , Thomas Zahnert and Edmund Koch
Published/Copyright: September 30, 2016
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Current Directions in Biomedical Engineering
From the journal Current Directions in Biomedical Engineering Volume 2 Issue 1

Abstract

The treatment of otitis media requires classifying the effusion in the tympanic cavity for choosing appropriate therapeutic strategies. Otoscopic examination of the middle ear depends on the expertise of the physician and is often hampered in case of inflammatory alterations of the tympanic membrane. In otologic research, optical coherence tomography is an innovative non-invasive imaging technique utilized for visualizing the tympanic membrane. This ex vivo study presents the possibility of OCT and Doppler-OCT for the detection of effusions in the tympanic cavity. Structural OCT imaging allows the direct visualization of scattering fluids behind the tympanic membrane. In addition, the measurement of the reduced oscillation amplitude by means of Doppler-OCT permits the indirect detection of scattering and transparent fluids.

Keywords: doppler; middle ear; optical coherence tomography; otitis media with effusion

1 Introduction

Otitis media is a frequently occuring disease of the middle ear with an increasing prevalence. At the age of one, at least 60% have already suffered from acute otits media [1]. In most cases, origin is a dysfunction of the eustachian tube, resulting in an accumulation of fluid in the tympanic cavity. In case of clear, serous fluid in the tympanic cavity, no antibiotic therapy is required. The progression of the disease leads to a mucous and purulent liquid filling of the tympanic cavity, requiring antibiotics for preventing severe complications and residual hearing loss. So far, the composition of the fluid in the tympanic cavity is difficult to determine non-invasively using the available diagnostics otoscopy and tympanometry. Thus, the selection of the appropriate therapy depends on the expertise of the physician, especially in case of inflammatory alterations.

In recent studies, optical coherence tomography (OCT) has been suggested as an innovative non-invasive diagnostic tool for the inspection of the middle ear. OCT is an interferometric imaging technique employing near infrared light for the depth-resolved visualization of superficial tissue with a spatial resolution of a few micrometers [2], [3].

OCT can be used for the three-dimensional visualization of the tympanic membrane and has been proposed, e. g., for the detection of scattering fluid located in the tympanic cavity [4], [5] and for the detection of bacterial biofilms behind the tympanic membrane [6]. In addition to the structural information, Doppler-OCT allows the measurement of the tympanic membrane oscillation [7], [8].

This ex vivo study investigates the capability of structural OCT imaging and Doppler-OCT imaging for the detection and differentiation of different fluid types with various filling levels in the human tympanic cavity.

2 Material and methods

2.1 Specimen preparation

For this ex vivo study, a freshly excised human temporal bone was used. Pathologic alterations were excluded via otoscopic examination by an ENT physician. The external ear channel was removed to provide access to the entire tympanic membrane. The sample was stored in a 0.9% saline solution before examination. For OCT imaging, the specimen was mounted using an articulated arm ensuring the orientation to be similar to a seating position of the patient.

Otitis media with effusion was simulated by filling the tympanic membrane with different fluids through the Eustachian tube. Therefore, a tube was inserted to the osseous part of the Eustachian tube. During the measurement, the filling level was kept constant by clamping this tube. The filling level was adjusted by means of otoscopy, ear microscopy and structural OCT imaging, if applicable. A serous and transparent fluid filling was simulated using 0.9% saline solution. The highly scattering purulent liquid filling was simulated using SMOFlipid (Fresenius Kabi Deutschland GmbH).

2.2 Optical coherence tomography

The swept source OCT-system utilizes a self-built laser source, which is a Fourier domain mode locked (FDML) laser [9] providing a line scan rate (A-scan rate) of 60 kHz. The acquisition time for volume scans and oscillation measurements is approximately 5.5 s. The center wavelength is 1300 nm and the bandwidth is typically 120 nm and can be modified for the adjustment of the maximum imaging depth. The emitted light is propagating to a scanner head containing a modified Michelson interferometer and two galvanometric scanners for three-dimensional image acquisition by means of telecentric scanning. The back scattered light propagates to a balanced detector, where the interference spectrum is measured in time multiplex. The A-scan is calculated thereof mainly by applying a Fourier transform. The axial and lateral resolution of the OCT-system is 14 μm and 11.5 μm, respectively. Details on the OCT system have been published in [7].

2.3 Measurement principle

For examining the middle ear, a three-dimensional image stack composed of 512 × 512 A-scans and a functional Doppler-OCT measurement were carried out for each simulated condition. The field of view was set to be 10 mm × 10 mm covering the entire tympanic membrane. For visualizing the position and orientation of the tympanic membrane, a depth-projection was calculated over the three-dimensional stack.

The oscillation of the tympanic membrane was acoustically stimulated using a loudspeaker. Simultaneously to the OCT-image acquisition, the applied sound pressure was measured using a probe tube microphone (ER-7C, Etymotic Research) positioned next to the tympanic membrane.

The membrane oscillation was measured on a 25 × 25 grid using Doppler-OCT. At each grid point, the tympanic membrane was stimulated using an acoustic chirp signal covering the frequency range from 500 Hz to 5 kHz, which is relevant for speech perception. The transfer functions were calculated via Fourier transform and via normalization with respect to the applied sound pressure. Thus, the transfer function provides the oscillation amplitude normalized to the sound pressure and resolved in frequency. Interpolated oscillation maps can be calculated in post-processing for frequencies within the excited frequency range. Details about the signal processing have been published in [7]. For grid points being affected by measurement errors due to limited reflectivity, e. g. at the border of the field of view or near to the umbo, the oscillation amplitude was manually set to zero.

3 Results and discussion

The results of the OCT measurements are summarized in Figure 1. Structural OCT imaging allowed the three-dimensional visualization of the tympanic membrane, which had a thickness of about 140 μm in the pars tensa area. The middle column in Figure 1 shows depth projections of three-dimensional OCT-scans illustrating the tympanic membrane orientation. Exemplary cross-sections corresponding to the red marked positions are shown in the right column. In these cross-sections, the funnel-like shape of the tympanic membrane is visible.

Figure 1 Left column: Normalized amplitude of the tympanic membrane oscillation at an oscillation frequency of 1168 Hz measured with Doppler-OCT. Middle column: Depth projections (intensity in arbitrary scale) over three-dimensional OCT image stacks. Right column: Cross-sections at the red marked position showing the tympanic membrane and the tympanic cavity below.
Figure 1

Left column: Normalized amplitude of the tympanic membrane oscillation at an oscillation frequency of 1168 Hz measured with Doppler-OCT. Middle column: Depth projections (intensity in arbitrary scale) over three-dimensional OCT image stacks. Right column: Cross-sections at the red marked position showing the tympanic membrane and the tympanic cavity below.

Liquid filling in the tympanic cavity is only directly visible by means of OCT if the fluid contains scattering particles. Thus, the SMOFlipid emulsion can be clearly identified as a substance with high backscattering intensity directly behind the tympanic membrane as well as areas with intensity enhancement in the depth projections. In case of 0.3 ml SMOFlipid, the fluid is located mainly behind the inferior quadrants of the tympanic membrane and the filling level is approximately reaching the umbo, the deepest point of the tympanic membrane. In case of the transparent NaCl-solution, the fluid itself cannot be visualized using structural OCT imaging, since it doesn’t contain any scattering particles. Only at some places the fluid-air interface causes additional reflexes.

In addition, Doppler OCT was used for the measurement of the tympanic membrane oscillation. In Figure 1, the normalized oscillation amplitude is shown in the left column for an oscillation frequency of 1168 Hz. Without pathological alternations, this frequency corresponds almost to an in-phase oscillation of the entire pars tensa. The normalized oscillation amplitude of the pars tensa is approximately 0.2 μm/Pa and has a maximum of 0.4 μm/Pa in the posterosuperior quadrant. At the manubrium of malleus, the oscillation amplitude is reduced.

An effusion in the tympanic cavity results in a decreased oscillation amplitude. Since the oscillation is widely damped at those areas of the tympanic membrane being in contact with the fluid, the estimation of the filling level is possible. This effect on the oscillation amplitude can be measured in case of both, scattering fluids (SMOFlipid) and transparent fluids (NaCl). In case of 0.3 ml SMOFlipid filling, the area of reduced oscillation amplitude is almost congruent to the area of liquid filling being visible in the corresponding depth-projection. The oscillation was examined at 1168 Hz, because nodal lines of the oscillation are not expected at this frequency. This facilitates the straightforward comparison and interpretation of the amplitude maps. In case of fluid filling, the measured oscillation amplitude was in the order of the detection limit. Thus, the oscillation amplitude was reduced at least to approximately 5%.

The extension to Doppler-OCT imaging permits the indirect detection of an effusion in the tympanic cavity for transparent and scattering fluids. In comparison, structural OCT imaging would not be able to visualize transparent effusions, which are free of scattering particles. Thus, Doppler OCT can improve the classification of effusions in the tympanic cavity. Additionally, the indirect detection of fluids could be necessary in case of tympanic membranes being less translucent due to inflammatory or degenerative alterations. These advantages might be essential using Doppler-OCT as a reliable tool in middle ear diagnostics.

4 Conclusion

This proof-of-principle study has investigated the ability of OCT to detect an effusion in the tympanic cavity. Standard OCT imaging measures the back scattering intensity and can be used for the visualization of scattering fluids. Structural OCT imaging alone is not suited for the detection of transparent fluid, where scattering particles are missing in the fluid.

The extension to Doppler-OCT allows the measurement of the tympanic membrane oscillation. The oscillation amplitude is reduced in areas of the tympanic membrane being in contact with fluid in the tympanic cavity. Thus, Doppler-OCT is suited for the indirect detection of scattering fluids and transparent fluids.

Author’s Statement

Research funding: The author state no funding involved. Conflict of interest: Authors state no conflict of interest. Material and Methods: Informed consent: Informed consent has been obtained from all individuals included in this study. Ethical approval: The research related to human use complies with all the relevant national regulations, institutional policies and was performed in accordance with the tenets of the Helsinki Declaration, and has been approved by the authors’ institutional review board or equivalent committee.

References

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Published Online: 2016-9-30
Published in Print: 2016-9-1

©2016 Lars Kirsten et al., licensee De Gruyter.

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.

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https://doi.org/10.1515/cdbme-2016-0098
Keywords for this article
doppler; middle ear; optical coherence tomography; otitis media with effusion
Creative Commons
BY-NC-ND 4.0

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  101. Designing a compact MRI motion phantom
  102. Cerebral cortex classification by conditional random fields applied to intraoperative thermal imaging
  103. Classification of indirect immunofluorescence images using thresholded local binary count features
  104. Analysis of muscle fatigue conditions using time-frequency images and GLCM features
  105. Numerical evaluation of image parameters of ETR-1
  106. Fabrication of a compliant phantom of the human aortic arch for use in Particle Image Velocimetry (PIV) experimentation
  107. Effect of the number of electrodes on the reconstructed lung shape in electrical impedance tomography
  108. Hardware dependencies of GPU-accelerated beamformer performances for microwave breast cancer detection
  109. Computer assisted assessment of progressing osteoradionecrosis of the jaw for clinical diagnosis and treatment
  110. Evaluation of reconstruction parameters of electrical impedance tomography on aorta detection during saline bolus injection
  111. Evaluation of open-source software for the lung segmentation
  112. Automatic determination of lung features of CF patients in CT scans
  113. Image analysis of self-organized multicellular patterns
  114. Effect of key parameters on synthesis of superparamagnetic nanoparticles (SPIONs)
  115. Radiopacity assessment of neurovascular implants
  116. Development of a desiccant based dielectric for monitoring humidity conditions in miniaturized hermetic implantable packages
  117. Development of an artifact-free aneurysm clip
  118. Enhancing the regeneration of bone defects by alkalizing the peri-implant zone – an in vitro approach
  119. Rapid prototyping of replica knee implants for in vitro testing
  120. Protecting ultra- and hyperhydrophilic implant surfaces in dry state from loss of wettability
  121. Advanced wettability analysis of implant surfaces
  122. Patient-specific hip prostheses designed by surgeons
  123. Plasma treatment on novel carbon fiber reinforced PEEK cages to enhance bioactivity
  124. Wear of a total intervertebral disc prosthesis
  125. Digital health and digital biomarkers – enabling value chains on health data
  126. Usability in the lifecycle of medical software development
  127. Influence of different test gases in a non-destructive 100% quality control system for medical devices
  128. Device development guided by user satisfaction survey on auricular vagus nerve stimulation
  129. Empirical assessment of the time course of innovation in biomedical engineering: first results of a comparative approach
  130. Effect of left atrial hypertrophy on P-wave morphology in a computational model
  131. Simulation of intracardiac electrograms around acute ablation lesions
  132. Parametrization of activation based cardiac electrophysiology models using bidomain model simulations
  133. Assessment of nasal resistance using computational fluid dynamics
  134. Resistance in a non-linear autoregressive model of pulmonary mechanics
  135. Inspiratory and expiratory elastance in a non-linear autoregressive model of pulmonary mechanics
  136. Determination of regional lung function in cystic fibrosis using electrical impedance tomography
  137. Development of parietal bone surrogates for parietal graft lift training
  138. Numerical simulation of mechanically stimulated bone remodelling
  139. Conversion of engineering stresses to Cauchy stresses in tensile and compression tests of thermoplastic polymers
  140. Numerical examinations of simplified spondylodesis models concerning energy absorption in magnetic resonance imaging
  141. Principle study on the signal connection at transabdominal fetal pulse oximetry
  142. Influence of Siluron® insertion on model drug distribution in the simulated vitreous body
  143. Evaluating different approaches to identify a three parameter gas exchange model
  144. Effects of fibrosis on the extracellular potential based on 3D reconstructions from histological sections of heart tissue
  145. From imaging to hemodynamics – how reconstruction kernels influence the blood flow predictions in intracranial aneurysms
  146. Flow optimised design of a novel point-of-care diagnostic device for the detection of disease specific biomarkers
  147. Improved FPGA controlled artificial vascular system for plethysmographic measurements
  148. Minimally spaced electrode positions for multi-functional chest sensors: ECG and respiratory signal estimation
  149. Automated detection of alveolar arches for nasoalveolar molding in cleft lip and palate treatment
  150. Control scheme selection in human-machine- interfaces by analysis of activity signals
  151. Event-based sampling for reducing communication load in realtime human motion analysis by wireless inertial sensor networks
  152. Automatic pairing of inertial sensors to lower limb segments – a plug-and-play approach
  153. Contactless respiratory monitoring system for magnetic resonance imaging applications using a laser range sensor
  154. Interactive monitoring system for visual respiratory biofeedback
  155. Development of a low-cost senor based aid for visually impaired people
  156. Patient assistive system for the shoulder joint
  157. A passive beating heart setup for interventional cardiology training
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