Jonas Golde

Imaging the tympanic membrane oscillation ex vivo with Doppler optical coherence tomography during simulated Eustachian catarrh

Recently, optical coherence tomography (OCT) was utilized in multiple studies for structural and functional imaging of the middle ear and the tympanic membrane. Since Doppler OCT allows both, the spatially resolved measurement of the tympanic membrane oscillation and high-resolution imaging, it is regarded as a promising tool for future in vivo applications. In this study, Doppler OCT is utilized for the visualization of the tympanic membrane oscillation in temporal bones with simulated Eustachian catarrh, which was realized by generating a depression in the tympanic cavity. The transfer function, meaning the oscillation amplitude normalized to the applied sound pressure, is measured frequency resolved in the range from 0.5 kHz to 6 kHz and with a lateral spatial resolution of 0.4 mm. Typical oscillation patterns could be observed in case of ambient pressure in the tympanic cavity. Under depression the characteristic oscillation patterns were observed with widely congruent appearance but at higher frequencies.

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

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.

In vivo imaging in the oral cavity by endoscopic optical coherence tomography

Abstract. The common way to diagnose hard and soft tissue irregularities in the oral cavity is initially the visual inspection by an experienced dentist followed by further medical examinations, such as radiological imaging and/or histopathological investigation. For the diagnosis of oral hard and soft tissues, the detection of early transformations is mostly hampered by poor visual access, low specificity of the diagnosis techniques, and/or limited feasibility of frequent screenings. Therefore, optical noninvasive diagnosis of oral tissue is promising to improve the accuracy of oral screening. Considering this demand, a rigid handheld endoscopic scanner was developed for optical coherence tomography (OCT). The novelty is the usage of a commercially near-infrared endoscope with fitting optics in combination with an established spectral-domain OCT system of our workgroup. By reaching a high spatial resolution, in vivo images of anterior and especially posterior dental and mucosal tissues were obtained from the oral cavity of two volunteers. The convincing image quality of the endoscopic OCT device is particularly obvious for the imaging of different regions of the human soft palate with highly scattering fibrous layer and capillary network within the lamina propria.

Visualization of interfacial adhesive defects at dental restorations with spectral domain and polarization sensitive optical coherence tomography

Abstract Restoration loss based on interfacial adhesive defects and associated caries at the restoration margin are the main causes for invasive replacement of dental restorations. Assessment of the interfacial quality based on clinical inspection and radiographic examination is often difficult and not reliable. In this work, we present spectral domain optical coherence tomography (SDOCT) and polarization sensitive optical coherence tomography (PSOCT) for the evaluation of tooth-composite bond failure. Imaging of two composite restorations at the occlusal surface are presented using intensity-based images obtained by SDOCT and PSOCT based degree of polarization uniformity (DOPU). Both modalities revealed several defects beneath the surface such as inhomogeneous adhesive layers, marginal gaps and bubbles. In addition, DOPU representation showed an inhomogeneous structure within the composite material. OCT based imaging of dental restorations could add a valuable diagnostic tool for the evaluation of structural defects in clinical practice. The representation of polarization characteristics with the DOPU algorithm provides further information on the homogeneity of the restoration.

Imaging of the human tympanic membrane by endoscopic optical coherence tomography

Abstract Endoscopic optical coherence tomography is a non-invasive and contactless imaging technique based on white light interferometry. It enables high-resolution three-dimensional imaging of scattering tissue up to a depth of about 2 mm. In addition, Doppler-OCT can detect sub-resolution movements. These features can be used to examine the tympanic membrane, the surrounding tissue and nearby areas of the tympanic cavity. For this purpose, we present an endoscopic OCT system, which provides access to the tympanic membrane. The design of the endoscope is based on a gradientindex (GRIN) lens system. This allows a broad field of view and a large working distance. An additional VIS beam path allows visual imaging and orientation inside the auditory canal. Therefore, illumination fibers are attached a round the GRIN-system. The resulting endoscope has a length of 55 mm and a diameter of 3.5 mm. By attaching an earphone and a probe microphone, the oscillation of the tympanic membrane can be measured under acoustic stimulation. With the endoscopic OCT system, we provide an examination tool for the diagnosis of a broad number of diseases like conductive hearing loss.

Cross-sectional and en-face depolarization imaging for the assessment of dental lesions

Abstract Dental caries is one of the most widespread diseases and the early and non-invasive detection of carious lesions remains an ongoing topic in biomedical research. In contrast, optical coherence tomography (OCT) is an emerging, non-invasive imaging technique for near-surface structures, that has already proved its capability for manifold biomedical applications and can be extended by several modalities such as polarization sensitivity. We have recently shown that polarization sensitive OCT combined with an algorithm for depolarization imaging, visualizing the degree of polarization uniformity (DOPU), is a promising tool for the detection and assessment of carious lesions. In this paper, we evaluate different visualization approaches based on both the intensity and DOPU data with cross-sectional and en-face representations and discuss limitations and the potential of the proposed method for the assessment of dental lesions on the example of a molar tooth with a brown spot.

Application of optical and spectroscopic technologies for the characterization of carious lesions in vitro

Abstract The detection of the beginning demineralization process of dental hard tissue remains a challenging task in dentistry. As an alternative to bitewing radiographs, optical and spectroscopic technologies showed promising results for caries diagnosis. The aim of the present work is to give an overview of optical and spectroscopic properties of healthy and carious human teeth in vitro by means of Raman spectroscopy (RS), optical coherence tomography (OCT) and hyperspectral imaging (HSI). OCT was able to represent microstructural changes below the enamel surface and revealed increased scattering for white spot lesions and a white scattering trail for deeper lesions. HSI showed similar absorbance characteristics for healthy and demineralized enamel over the entire spectrum and a characteristic absorbance peak at 550 nm for discolored lesions. Already at early carious stages (white spot), we found a distinct loss of hydroxylapatite-related intensity at 959 cm−1 in demineralized regions with RS. Healthy and demineralized tooth surfaces can be distinguished at different signal levels by means of RS, OCT and HSI. The presented modalities provide additional information to the current clinical diagnosis of caries such as microstructural changes, quantification of the demineralization and imaging of caries-related chemical changes.

In vivo imaging of human oral hard and soft tissues by polarization-sensitive optical coherence tomography

Abstract. Since optical coherence tomography (OCT) provides three-dimensional high-resolution images of biological tissue, the benefit of polarization contrast in the field of dentistry is highlighted in this study. Polarization-sensitive OCT (PS OCT) with phase-sensitive recording is used for imaging dental and mucosal tissues in the human oral cavity in vivo. An enhanced polarization contrast of oral structures is reached by analyzing the signals of the co- and crosspolarized channels of the swept source PS OCT system quantitatively with respect to reflectivity, retardation, optic axis orientation, and depolarization. The calculation of these polarization parameters enables a high tissue-specific contrast imaging for the detailed physical interpretation of human oral hard and soft tissues. For the proof-of-principle, imaging of composite restorations and mineralization defects at premolars as well as gingival, lingual, and labial oral mucosa was performed in vivo within the anterior oral cavity. The achieved contrast-enhanced results of the investigated human oral tissues by means of polarization-sensitive imaging are evaluated by the comparison with conventional intensity-based OCT.

Polarization sensitive optical coherence tomography utilizing a buffered swept source laser

Abstract We present an approach for polarization sensitive optical coherence tomography (PS-OCT) that solely requires a modification of the light source, a buffered swept source laser. For this purpose a single-mode fiber-based Fourier domain mode locked laser is extended by fourfold buffering with manual fiber polarization controllers to emit alternating sweep polarizations, while the polarization contrast calibration is realized by a high-speed polarimeter. As the introduced setup utilizes standard scanning and detection units, the proposed method is a promising way to enhance various swept source OCT systems by polarization sensitive imaging. Preliminary measurements of a human finger nail with different polarization contrasts demonstrate the feasibility of the concept.

Functional and morphological imaging of the human tympanic membrane with endoscopic optical coherence tomography

Abstract In this ex vivo feasibility study, endoscopic structural and functional optical coherence tomography (OCT) imaging with a field of view of 8 mm is presented allowing the inspection of nearly the entire tympanic membrane through the ear canal. The endoscope utilizes a gradient index optics for simultaneous OCT and video endoscopy. Additionally, Doppler-OCT allows the measurement of the tympanic membrane oscillation. Due to the fast image acquisition, only minor motion artifacts have been observed, which don’t affect the image quality. In conclusion, endoscopic OCT is considered as a promising tool for the comprehensive examination of the human middle ear.