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The analysis of limits for multimode fibre imaging
Štolzová, Hana ; Kozubek, Michal (oponent) ; Dostál, Zbyněk (vedoucí práce)
Multimode fibers are the imaging tool of a significant potential in in-vivo microendoscopy. Recently, this method has seen a great development, thanks to the improvements in computational and other technologies, such as digital spatial light modulation. The aim of this work was to find specific limits of multimode fiber imaging and to present their computer simulation. The effect of illumination of the optical system containing the multimode fiber on its focussing and imaging capability was investigated. By analysing the data obtained from simulations and experiments, it has been found that the various levels of the Gaussian beam truncation by a projected multimode fiber numerical aperture results in a significant variance in the imaging capabilities of the system. Therefore, it seems that the multimode optical fibers are not a completely random medium. Observing the quality of the focusing, it was found that low truncated beams (beam-waist around 50% of the projected fiber numerical aperture), have the highest performance. This fact was verified by experimental measurements. Imaging using similarly truncated beams showed the best contrast transmission capability. However, when analysing the resolution of two pointlike objects, the beams with a significantly larger waist and a higher degree of truncation, of 100% or more, were most appropriate. The presence of this difference forces the person using the imaging system containing the multimode fiber to consider several aspects, in what environment the particular optical system will be used and which imaging quality indicator will be considered the most important.
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Příprava a analýza vláknových sond pro holografický mikroendoskop
Černá, Eliška ; Průša, Stanislav (oponent) ; Jákl, Petr (vedoucí práce)
Tato práce se zabývá přípravou a analýzou vláknových sond pro holografický mikroendoskop. Vlákna jsou specificky broušena a pomocí depozice tenkých vrstev je na ně nanášena odrazná vrstva hliníku nebo stříbra. Vlastnosti těchto nanesených vrstev jsou dále zkoumány a vyhodnocovány pomocí AFM, profilometru a měřící aparatury pro zhodnocení odrazivosti. Z naměřených dat je vytvořen protokol, který popisuje výrobu vláknových sond s optimálními parametry pro holografickou mikroendoskopii. Takto vytvořené vláknové sondy by mohly mít přínos v diagnostice neurodegenerativních onemocnění jako je Alzheimerova nebo Parkinsonova choroba.
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In vivo application of holographic endoscopy
Tučková, Tereza ; Brzobohatý,, Oto (oponent) ; Bouchal, Petr (oponent) ; Uhlířová, Hana (vedoucí práce)
The progress in understanding of complex brain function is conditioned by the ability to optically access any chosen structure and area in the living brain with minimal tissue damage and with sub-cellular resolution, The progress in accessing deeper into the light-scattering tissue stands nowadays largely on the development of optical endoscopic probes such as microendoscopes with incorporated graded index (GRIN) lenses and fibre-optic bundles. Due to recent advancements in holographic light shaping methodology, using multimode optical fibres (MMF) as imaging elements has become promising for high resolution imaging deep in the tissue. In comparison to GRIN-based endoscopes and fibre bundles endoscopes, MMFs provide the highest ratio of image resolution and probe thickness causing minimal tissue damage. This thesis first provides an overview of the current state-of-the-art in vivo deep brain imaging technology, multi-mode fibre-based endoscopy and its principles to introduce the related technology. The main technological focus of the thesis stands on using a digital micro-mirror device (DMD) to modulate light through the MMF probes. This enables fast raster scanning of the fluorescent sample at the imaging plane of the fibre distal facet. An optical setup exploiting this principle has been built, its imaging properties carefully evaluated, and high stability reached. Its imaging abilities have been demonstrated on 2D and 3D fluorescent phantom samples. Consequently, we have developed an image post-processing procedure to enhance the detected image and reach the full diffraction-limited resolution potential. Using algorithms, one based on a regularised iterative inversion and second on regularised direct pseudo-inversion, lead to enhancement of the image contrast and resolution. Further, we used genetically modified mice to move towards ex vivo and in vivo imaging. Suitable mouse models were identified and its ex vivo brain imaging showed that the images suffer from strong background fluorescent signal from out-of-focus planes. Therefore, further work focused on technological development for light attenuation based on the confocal principle. An optical setup for confocal “pinhole” filtration has been built using a custom-made probe consisting of graded-index MMF spliced at the tip of the step-index MMF and a second DMD. The fluorescent signal collected by the GRIN-SI-MMF was filtered in the probe far field where for every scanning focal point it forms an annular ring. This ring-signal, and thus also the out-of-focus signal, was then separated using a mask on DMD2. On a set of experiments using phantom sample of fluorescent microspheres and fixed brain tissue it has been demonstrated that this confocal filtering leads to attenuation of the background signal, the signal from the out-of-focus planes thus enhancing the images contrast and resolution. This principle of confocal filtering in the holographic endoscope has been also demonstrated using a novel side-view MMF probe. This work shows a piece of a puzzle in a long-term complex development of an optimal tool for deep-tissue and high-resolution imaging. The MMF-based holographic endoscope has been advanced to routine imaging of biological tissue in range of hours with the feature of out-of-focus light attenuation. The endoscope has been tested on imaging of phantom samples as well as fixed mouse brain slices and in vivo vasculature down to depth of 5 mm.
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The analysis of limits for multimode fibre imaging
Štolzová, Hana ; Kozubek, Michal (oponent) ; Dostál, Zbyněk (vedoucí práce)
Multimode fibers are the imaging tool of a significant potential in in-vivo microendoscopy. Recently, this method has seen a great development, thanks to the improvements in computational and other technologies, such as digital spatial light modulation. The aim of this work was to find specific limits of multimode fiber imaging and to present their computer simulation. The effect of illumination of the optical system containing the multimode fiber on its focussing and imaging capability was investigated. By analysing the data obtained from simulations and experiments, it has been found that the various levels of the Gaussian beam truncation by a projected multimode fiber numerical aperture results in a significant variance in the imaging capabilities of the system. Therefore, it seems that the multimode optical fibers are not a completely random medium. Observing the quality of the focusing, it was found that low truncated beams (beam-waist around 50% of the projected fiber numerical aperture), have the highest performance. This fact was verified by experimental measurements. Imaging using similarly truncated beams showed the best contrast transmission capability. However, when analysing the resolution of two pointlike objects, the beams with a significantly larger waist and a higher degree of truncation, of 100% or more, were most appropriate. The presence of this difference forces the person using the imaging system containing the multimode fiber to consider several aspects, in what environment the particular optical system will be used and which imaging quality indicator will be considered the most important.
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