Universität zu Lübeck
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Item 4D Fluss MRT zur Analyse der aortalen Wandschubspannung auf Basis verschiedener Software-Lösungen(2019) Beldoch, Michael PeterItem 4D Fluss MRT zur Analyse der thorakalen aortalen Flusscharakteristika bei Patienten mit Sinusprothese(2017) Oechtering, Thekla H.Item 850 nm Fourier domain mode-locked laser for ophthalmic optical coherence tomography imaging(2025) Klufts, MarieNon-invasive imaging techniques have become essential in medical diagnostics over the past few decades. Among these, Optical Coherence Tomography (OCT) offers micrometer resolution with millimeter-scale depth penetration, making it particularly valuable in ophthalmology. OCT captures backscattered light to generate 3D volumes. For eye imaging, wavelengths around 850 nm are ideal due to minimal absorption by the vitreous and high scattering in the upper retinal layers. Imaging speed is also critical, as faster speeds reduce motion artifacts. Swept-source OCT, using wavelength-tunable lasers, enables high-speed imaging. Fourier Domain Mode-Locked (FDML) lasers providing megahertz-level scan rates are ideal for this purpose. This thesis explores the development and application of FDML lasers for ophthalmic imaging. Unlike other tunable lasers, FDML lasers have a unique design that stores a full sweep in their fiber cavity for hundreds of round trips, avoiding rebuilding of lasing from spontaneous emission after tuning to new wavelengths offering high phase stability and long coherence length necessary for high quality OCT images. A new megahertz FDML laser at 850 nm would merge the unique advantages of this wavelength with the proven benefits of FDML lasers allowing for a low latency, dynamic view of the retina, opening new doors for real-time diagnostics. The first part delves into the challenges of developing an FDML laser around 850 nm, addressing issues like polarization mode dispersion, chromatic dispersion, and low gain/loss ratios. These factors contribute to the complexity of managing short wavelength OCT lasers, which explain their scarcity to date. The second part presents in-vivo ophthalmic OCT imaging results, with comparisons to other imaging techniques. The newly designed FDML laser demonstrates strong performance for OCT imaging, achieving an axial resolution below 10 µm, sensitivity above 84 dB, and a ranging depth of 1.4 cm. Also, its high phase stability, with a time jitter of 25 ps over 1,000 sweeps, makes it suitable for phaseresolved techniques. Retinal images were captured at 414,000 axial scans per second using a master-slave based calibration technique, at 828 kHz with bidirectional sweeping, and at 1.7 MHz using optical buffering with a single-k-calibration technique. While increased scattering at 850 nm limits choroidal imaging, most retinal layers of interest are clearly visible. This FDML laser highlights the advantages of short-wavelength, high-speed imaging and paves the way for new applications.Item A Fourier-analytical approach for field-free-point magnetic particle imaging(2025) Maaß, MarcoMagnetic particle imaging is a tracer-based medical imaging technique that measures the spatial distribution of superparamagnetic nanoparticles. Alternating magnetic fields with different excitation sequences are used to measure the nanoparticle distribution in a scanner. Usually, the simplified Langevin model of paramagnetism is used as a first approximation for the complicated nonlinear magnetization behavior of nanoparticles. Although the modified Langevin model of paramagnetism can provide suitable image reconstructions for one-dimensional excitation, the situation is more complicated for higher-dimensional excitation, as several aspects cannot be fully explained by the Langevin model. A well-known example is the spatial similarity of the frequency components of the system function with tensor products of Chebyshev polynomials. This was observed for a higher-dimensional excitation of the Lissajous trajectory type and was unproven for almost ten years. With the aim of explaining such observations mathematically, this thesis makes an important contribution to the mathematical foundations of magnetic particle imaging. To this end, the spatio-temporal system function based on the Langevin model is transformed into the frequency domain using various concepts of Fourier analysis. The scientific contribution of the newly developed mathematical framework is manifold. Firstly, the developed model is able to separate the scanner-dependent excitation from the particle magnetization model, allowing better utilization of the imaging operator so that faster reconstruction methods could be developed. Secondly, it is now easier to investigate both the effect of the magnetization model and that of the excitation sequence in the imaging model separately. Thus, an extended equilibrium magnetization model is introduced in this thesis and a series representation is developed for it. Furthermore, the exact relationship between the frequency components of the system function and the tensor products of Chebyshev polynomials is shown for excitations of the Lissajous trajectory type. Finally, using the developed mathematical framework, the frequency representations of various excitation sequences known from the literature are calculated, which further increases the applicability of the model for magnetic particle imaging.Item A metabolomics and lipidomics profile of ischemic stroke(2022) Folberth, JuliaItem Abhängigkeit des Bereitschaftspotentials vom zeitlichen Rahmen und der Aufmerksamkeit(2021) Baur, Alexandra ElisabethItem ABS-Interventionen bei intensivmedizinisch versorgten septischen Patienten(2022) Gansewig, Bente AnekeItem Abscheiden von Schichten aus Poly-Parylen für medizinische Zwecke am Beispiel der künstlichen Blase(2014) Schamberger, FlorianItem Active contours with spatially-variant definitions of energy terms based on local region descriptors(2008) Darolti, CristinaItem Adaptation of Mycobacterium tuberculosis complex strains to antibiotics(2023) Sonnenkalb, Lindsay Ruth