As dental caries is one of the most common diseases, the early and noninvasive detection of carious lesions plays an important role in public health care. Optical coherence tomography (OCT) with its ability of depth-resolved, high-resolution, noninvasive, fast imaging has been previously recognized as a promising tool in dentistry. Additionally, polarization sensitive imaging provides quantitative measures on the birefringent tissue properties and can be utilized for imaging dental tissue, especially enamel and dentin. By imaging three exemplary tooth samples ex vivo with proximal white spot, brown spot, and cavity, we show that the combination of polarization sensitive OCT and the degree of polarization uniformity (DOPU) algorithm is a promising approach for the detection of proximal carious lesions due to the depolarization contrast of demineralized tissue. Furthermore, we investigate different sizes of the DOPU evaluation kernel on the resulting contrast and conclude a suitable value for this application. We propose that DOPU provides an easy to interpret image representation and appropriate contrast for possible future screening applications in early caries diagnostics.

Magnetresonanztomographie (MRT) ist eine nichtinvasive Bildgebungsmethode, die in der Medizin sowie in der Forschung eingesetzt wird und auf der magnetischen Kernresonanz beruht. Die Erforschung der Ultrahochfeld (UHF) MRT ab Magnetfeldstärken von 7.0 Tesla und darüber ist durch einen intrinsischen Signalgewinn hin zu hohen Magnetfeldstärken motiviert und beschäftigt sich mit den dabei auftretenden physikalischen Effekten ebenso wie mit den dazu notwendigen neuartigen Technologien. Die vorliegende Arbeit untersucht Mehrkanalantennen zur Anregung der magnetischen Kernresonanz sowie zum Empfang des resultierenden Signals bei 7.0 T. Für die magnetische Kernresonanz von Protonen ergibt sich eine Resonanzfrequenz von 300 MHz. Die zugehörige Wellenlänge in menschlichem Gewebe verlässt in diesem Frequenzbereich im Verhältnis zu den Körperabmessungen den quasistatischen Bereich. Die sich ergebende Wellenausbreitung hat Interferenzmuster in den erzeugten Bildern zur Folge, die zu klinisch nicht verwertbaren Bildinformationen führen können. Vor diesem Hintergrund wurden in dieser Arbeit Mehrkanalantennen mit 4, 8 und 16 unabhängigen Elementen zur Signalanregung und zum Empfang konzipiert, aufgebaut und untersucht. Die Erkenntnisse mündeten in der erfolgreichen Implementierung der weltweit ersten 32-Kanal Antenne zur kardiovaskulären Bildgebung bei 7.0 T. Darüber hinaus wurde eine Antenne entwickelt, welche die ersten auf der Natriumkonzentration beruhenden bewegten MRT Bilder des menschlichen Herzens bei 7.0 T ermöglichte. Der Zusammenhang zwischen Natriumkonzentration und Zellintegrität ermöglicht direkte und ortsaufgelöste Einblicke in physiologische Prozesse. Die Ergebnisse dieser Arbeit belegen die breite Anwendbarkeit von Mehrkanalantennen in der UHF MRT zur Protonen-und Natriumbildgebung und bilden eine solide technologische Basis für breitere klinische Studien, um die Ultrahochfeld MRT reif für den routinemäßigen Einsatz im Gesundheitswesen zu machen. / Magnetic resonance imaging (MRI) is a non-invasive imaging method based on the effect of nuclear magnetic resonance. It is used in healthcare as well as in research. MRI at magnetic field strengths of 1.5 Tesla and 3 Tesla is well established. The gain in signal-to-noise ratio (SNR) intrinsic to higher magnetic field strength fuels the vigorous research field of Ultrahigh field (UHF) MRI at 7.0 T and above. Nevertheless for MRI based upon proton imaging the wavelength of the transmitted electro-magnetic fields slowly departs from the semi-static regime and reaches the dimension of the transection of the human body at 7.0 T. This gives rise to constructive and destructive interferences that potentially render image quality non-diagnostic for clinical use. Therefore is work proposes the worlds’ first 32 channel antenna array for cardiovascular MRI at 7.0 T. Electro-magnetic field simulations are utilized to study the capabilities of multi-channel RF antenna arrays to mitigate destructive interferences and provided the basis for a workflow towards homogenization of the electromagnetic radio-frequency field. Pre-clinical studies showed the capabilities and limits of translating the SNR gain of UHF MRI into clinical beneficial numbers, namely increased spatial or temporal resolution or scan time shortening. To make further use of the benefits of UHR MRI and to make a step towards first-hand spatial resolved information of biological processes in human tissue sodium imaging of the human heart was enabled with the design of a tailored antenna array. The results were reconstructed into the first movies of the human heart at 7.0 T based on sodium signal. This profound technological basis for radio frequency excitation and reception in UHF MRI can be expected to pave the way for broader clinical studies at 7.0 T with the ultimate goal to improve the quality and the earliness of treatment decisions in future clinical practice.

It is of large importance to identify abnormalities and pathologies of the oral mucosa. In this perspective, the use of non-invasive optical techniques such as OCT provides the opportunity to complement common diagnostics. Especially in cases of recurrent or multiple lesions, OCT diagnosing promises a thorough and, if necessary, repeated assessment of the oral mucosa without the drawbacks of invasive procedures. For this reason, the number of studies on in vivo OCT examination of suspicious oral mucosal lesions is continually increasing. At the same time, there are only a few studies focusing on imaging pathologically altered oral mucosa. Against this background, the aim of this work was to characterize pathological oral mucosa with the clinical diagnosis of OLP in various areas of the oral cavity and additionally diagnose it using OCT imaging. An endoscopic in vivo OCT examination, in addition to conventional diagnostics, was conducted on 22 adult patients. The examination involved three measurement points, but only two were included for further analysis: the pathological center and the transition to healthy mucosa. Subsequently, image analysis was performed based on qualitative criteria to assess the oral mucosa. The parameters for examining OCT scans included EP thickness, delineation/visibility of the basement membrane, EP reflectivity, LP reflectivity and visible vascular network in the lamina propria. For classified OLP in general, the structural changes in the oral mucosa were compared to the normal state and the parameters of healthy oral mucosa served as a basis for determining the altered morphology in OCT, depending on the clinical classification of OLP. This made it possible to derive OLP-specific features in OCT. The goal of this dissertation was also to relate in vivo depth-resolution cross-sectional image information from OCT to the clinical diagnosis and compare certain parameters of different OLP forms. The transition from a normal to a pathological finding is sometimes clinically challenging to define, as is the appropriate area for a biopsy in an extensive and widespread oral lesion or alteration. In the future, non-invasive optical biopsy could be helpful in this regard. In this case series, as a first step, OCT cross-sectional images of central and peripheral areas of various types and subtypes of OLP were non-invasively captured and correlated with visual clinical findings and, if available, with histopathology. By identifying and describing OLP-specific features in OCT cross-sections for different forms of OLP, we establish a foundation for the non-invasive differentiation of suspicious dysplastic lesions from OLP and other pathology was established. This may improve biopsy sampling in the future and ensure reliable histopathological assessment. The next step is to further investigate the proposed OCT technology in clinical studies with a larger number of cases, obtaining robust data on the sensitivity and specificity of OCT for distinguishing various forms of OLP, as well as for distinguishing dysplastic changes and squamous cell carcinomas.