Anke Burkhardt

Optical coherence tomography in biomedical research.

Optical coherence tomography (OCT) is a noninvasive, high-resolution, interferometric imaging modality using near-infrared light to acquire cross-sections and three-dimensional images of the subsurface microstructure of biological specimens. Because of rapid improvement of the acquisition speed and axial resolution of OCT over recent years, OCT is becoming increasingly attractive for applications in biomedical research. Therefore, OCT is no longer used solely for structural investigations of biological samples but also for functional examination, making it potentially useful in bioanalytical science. The combination of in vivo structural and functional findings makes it possible to obtain thorough knowledge on basic physiological and pathological processes. Advanced applications, for example, optical biopsy in visceral cavities, have been enabled by combining OCT with established imaging modalities. This report gives an outline of the state of the art and novel trends of innovative OCT approaches in biomedical research in which the main focus is on applications in fundamental research and pre-clinical utilization.

Investigation of the human tympanic membrane oscillation ex vivo by Doppler optical coherence tomography.

Investigations of the tympanic membrane (TM) can have an important impact on understanding the sound conduction in the ear and can therefore support the diagnosis and treatment of diseases in the middle ear. High-speed Doppler optical coherence tomography (OCT) has the potential to describe the oscillatory behaviour of the TM surface in a phase-sensitive manner and additionally allows acquiring a three-dimensional image of the underlying structure. With repeated sound stimuli from 0.4 kHz to 6.4 kHz, the whole TM can be set in vibration and the spatially resolved frequency response functions (FRFs) of the tympanic membrane can be recorded. Typical points, such as the umbo or the manubrium of malleus, can be studied separately as well as the TM surface with all stationary and wave-like vibrations. Thus, the OCT methodology can be a promising technique to distinguish between normal and pathological TMs and support the differentiation between ossicular and membrane diseases.

Endoscopic optical coherence tomography device for forward imaging with broad field of view

One current challenge of studying human tympanic membranes (TM) with optical coherence tomography (OCT) is the implementation of optics that avoid direct contact with the inflamed tissue. At the moment, no commercial device is available. We report an optics design for contactless forward imaging endoscopic optical coherence tomography (EOCT) with a large working distance (WD) and a broad field of view (FOV) by restricting the overall diameter of the probe to be small (3.5 mm), ensuring a sufficient numerical aperture. Our system uses a gradient-index (GRIN) relay lens and a GRIN objective lens, and executes a fan-shaped optical scanning pattern. The WD and FOV can be adjusted by manually changing the distance between the triplet and the GRIN relay lens. The measured lateral resolution is ∼28  μm at a WD of 10 mm with a FOV of 10 mm. Additionally, a camera and an illumination beam path were implemented within the probe for image guidance during investigations of the TM. We demonstrated the performance of the EOCT design by 3-D imaging of a human TM ex vivo and in vivo with a k-linear spectral domain OCT system.

Endoscopic optical coherence tomography for imaging the tympanic membrane

Optical coherence tomography (OCT) is an imaging modality that enables micrometer-scale contactless subsurface imaging of biological tissue. Endoscopy, as another imaging method, has the potential of imaging tubular organs and cavities and therefore has opened up several application areas not accessible before. The combination of OCT and endoscopy uses the advantages of both methods and consequently allows additional imaging of structures beneath surfaces inside cavities. Currently, visual investigations on the surface of the human tympanic membrane are possible but only with expert eyes. up to now, visual imaging of the outer ear up to the tympanic membrane can be carried out by an otoscope, an operating microscope or an endoscope. In contrast to these devices, endoscopy has the advantage of imaging the whole tympanic membrane with one view. The intention of this research is the development of an endoscopic optical coherence tomography (EOCT) device for imaging the tympanic membrane depth-resolved and structures behind it. Detection of fluids in the middle ear, which function as an indicator for otitis media, could help to avoid the application of antibiotics. It is possible to detect a congeries of fluids with the otoscope but the ambition is to the early detection by OCT. The developed scanner head allows imaging in working distances in the range from zero up to 5 mm with a field of view of 2 mm. In the next step, the scanner head should be improved to increase the working distance and the field of view.

Non-invasive imaging and monitoring of rodent retina using simultaneous dual-band optical coherence tomography

Spectral domain dual-band optical coherence tomography for simultaneous imaging of rodent retina in the 0.8 μm and 1.3 μm wavelength region and non-invasive monitoring of the posterior eye microstructure in the field of retinal degeneration research is demonstrated. The system is illuminated by a supercontinuum laser source and allows three-dimensional imaging with high axial resolution better than 3.8 μm and 5.3 μm in tissue at 800 nm and 1250 nm, respectively, for precise retinal thickness measurements. A fan-shaped scanning pattern with the pivot point close to the eyes pupil and a contact lens are applied to obtain optical access to the eyes fundus. First in vivo experiments in a RCS (royal college of surgeons) rat model with gene-related degeneration of the photoreceptor cells show good visibility of the retinal microstructure with sufficient contrast for thickness measurement of individual retinal layers. An enhanced penetration depth at 1250 nm is clearly identifiable revealing sub-choroidal structures that are not visible at 800 nm. Furthermore, additional simultaneous imaging at 1250 nm improves image quality by frequency compounding speckle noise reduction. These results are encouraging for time course studies of the rodent retina concerning its development related to disease progression and treatment response.

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.

Optical coherence tomography as approach for the minimal invasive localization of the germinal disc in ovo before chicken sexing

In most industrial states a huge amount of newly hatched male layer chickens are usually killed immediately after hatching by maceration or gassing. The reason for killing most of the male chickens of egg producing races is their slow growth rate compared to races specialized on meat production. When the egg has been laid, the egg contains already a small disc of cells on the surface of the yolk known as the blastoderm. This region is about 4 - 5 mm in diameter and contains the information whether the chick becomes male or female and hence allows sexing of the chicks by spectroscopy and other methods in the unincubated state. Different imaging methods like sonography, 3D-X-ray micro computed tomography and magnetic resonance imaging were used for localization of the blastoderm until now, but found to be impractical for different reasons. Optical coherence tomography (OCT) enables micrometer-scale, subsurface imaging of biological tissue and could therefore be a suitable technique for an accurate localization. The intention of this study is to prove if OCT can be an appropriate approach for the precise in ovo localization.

Vibration of the human tympanic membrane measured with OCT in a range between 0.4 kHz and 6.4 kHz on an ex vivo sample

Vibrations of the tympanic membrane (TM) play a key role for the transmission of sound to the inner ear. Today, there exist still problems in measuring the movement of the TM and there are unresolved issues in understanding the TM and its behavior. A non-invasive and contact-free in vivo investigation of the structure and the functional behavior of the TM would be a big step forward. In the presented study, the suitability of optical coherence tomography (OCT) for measuring the oscillation patterns of the TM in the frequency range covering the range of the human speech perception should be tested. For functional imaging a sound chirp was generated in the frequency range between 0.4 kHz - 6.4 kHz. To obtain the movement within a sufficient resolution, a grid of 25 x 25 measurement points was generated over the whole TM. The information of the oscillatory movement was encoded in the Doppler signal, provided by M-scans at several points of the TM. The frequency response functions of each frequency showed different oscillation patterns on the TM. The acquisition time of one single M-scan was only 8.5 ms and of the entire TM 5.3 s, emphasizing the potential of the method for future in vivo applications. Furthermore, the morphology was acquired with the same OCT-system, showing the feasibility for structural imaging and differentiation between typical regions of the TM. Thus, OCT was shown as a suitable method for the simultaneous measurement of the functional and structural behavior of the TM.

Minimal invasive localization of the germinal disc in ovo for subsequent chicken sexing using optical coherence tomography

Reason for using optical coherence tomography (OCT) to locate the germinal disc is the questionable and ethically alarming killing of male layer chickens because for the layer line only the females are necessary. To avoid this and to protect the animal rights, the sex of the fertilized chicken egg has to be determined as early as possible in the unincubated state. Because the information whether the chick becomes male or female can be found in the germinal disc an accurate localization for sexing is essential. The germinal disc is located somewhere on top of the yolk and has a diameter of approximately 4 - 5 mm. Different imaging methods like ultrasonography, 3D-X-ray micro computed tomography and magnetic resonance imaging were used for localization until now, but found to be impractical. The goal of this study is to prove if OCT can be a moderate approach for the precise in ovo localization. Because the eggshell is an impenetrable barrier for OCT and to minimize the penetration of germs a very small hole is placed in the eggshell and a fan-shaped optical scanning pattern is used.