Test der Speziellen Relativitätstheorie mittels Laserspektroskopie an relativistischen 7 Li +-Ionen am ESR

Die Invarianz physikalischer Gesetze unter Lorentztransformationen ist eines der fundamentalen Postulate der modernen Physik und alle Theorien der grundlegenden Wechselwirkungen sind in kovarianter Form formuliert. Obwohl die Spezielle Relativitätstheorie (SRT) in einer Vielzahl von Experimenten mit hoher Genauigkeit überprüft und bestätigt wurde, sind aufgrund der weitreichenden Bedeutung dieses Postulats weitere verbesserte Tests von grundsätzlichem Interesse. Darüber hinaus weisen moderne Ansätze zur Vereinheitlichung der Gravitation mit den anderen Wechselwirkungen auf eine mögliche Verletzung der Lorentzinvarianz hin. In diesem Zusammenhang spielen Ives-Stilwell Experimente zum Test der Zeitdilatation in der SRT eine bedeutende Rolle. Dabei wird die hochauflösende Laserspektroskopie eingesetzt, um die Gültigkeit der relativistischen Dopplerformel – und damit des Zeitdilatationsfaktors γ – an relativistischen Teilchenstrahlen zu untersuchen. Im Rahmen dieser Arbeit wurde ein Ives-Stilwell Experiment an 7Li+-Ionen, die bei einer Geschwindigkeit von 34 % der Lichtgeschwindigkeit im Experimentierspeicherring (ESR) des GSI Helmholtzzentrums für Schwerionenforschung gespeichert waren, durchgeführt. Unter Verwendung des 1s2s3S1→ 1s2p3P2-Übergangs wurde sowohl Λ-Spektroskopie als auch Sättigungsspektroskopie betrieben. Durch die computergestützte Analyse des Fluoreszenznachweises und unter Verwendung optimierter Kantenfilter für den Nachweis konnte das Signal zu Rauschverhältnis entscheidend verbessert und unter Einsatz eines zusätzlichen Pumplasers erstmals ein Sättigungssignal beobachtet werden. Die Frequenzstabilität der beiden verwendeten Lasersysteme wurde mit Hilfe eines Frequenzkamms spezifiziert, um eine möglichst hohe Genauigkeit zu erreichen. Die aus den Strahlzeiten gewonnen Daten wurden im Rahmen der Robertson-Mansouri-Sexl-Testtheorie (RMS) und der Standard Model Extension (SME) interpretiert und entsprechende Obergrenzen für die relevanten Testparameter der jeweiligen Theorie bestimmt. Die Obergrenze für den Testparameter α der RMS-Theorie konnte gegenüber den früheren Messungen bei 6,4 % der Lichtgeschwindigkeit am Testspeicherring (TSR) des Max-Planck-Instituts für Kernphysik in Heidelberg um einen Faktor 4 verbessert werden.

Das Aerosol-Ionenfallen-Massenspektrometer (AIMS) : Aufbau, Charakterisierung und Feldeinsatz

Um die in der Atmosphäre ablaufenden Prozesse besser verstehen zu können, ist es wichtig dort vorhandene Partikel gut charakterisieren zu können. Dazu gehört unter anderem die Bestimmung der chemischen Zusammensetzung der Partikel. Zur Analyse insbesondere organischer Partikel wurde dazu in einer früheren Promotion das Aerosol-Ionenfallen-Massenspektrometer (AIMS) entwickelt.Im Rahmen dieser Arbeit wurden Entwicklungsarbeiten durchgeführt, um die Charakteristiken des Prototypen zu verbessern sowie es für den Feldeinsatz tauglich zu machen. Die durchgeführten Veränderungen betreffen mechanische und elektrische Komponenten sowie das LabView Steuerungsprogramm. So wurde z.B. die Ionenquelle derart modifiziert, dass die Ionen nicht mehr permanent erzeugt werden, sondern nur innerhalb des Zeitraums wenn sie auch in der Ionenfalle gespeichert werden können. Durch diese Modifikation konnte das Signal-zu-Rausch Verhältnis deutlich verbessert werden. Nach Beendigung der Umbauten wurden in ausführlichen Laborstudien die einzelnen Instrumentenparameter detailliert charakterisiert. Neben den Spannungen die zur Fokussierung oder zur Speicherung der Ionen in der Ionenfalle dienen, wurden die unterschiedlichen Arten der resonanten Anregung, mittels der die Ionen in der Ionenfalle gezielt zu Schwingungen angeregt werden können, sehr genau untersucht. Durch eine gezielte Kombination der unterschiedlichen Arten der resonanten Anregung ist es möglich MSn-Studien durchzuführen. Nach erfolgreicher Charakterisierung konnte in weiteren Laborstudien die MSn-Fähigkeit des AIMS demonstriert werden. Für Tryptophan (C11H12N2O2) wurde anhand von MS4-Studien ausgehend von m/z 130 ein möglicher Fragmentierungsweg identifiziert. Für die einzelnen Stufen der MS4-Studien wurden die Nachweisgrenzen abgeschätzt. Im Rahmen der PARADE (PArticles and RAdicals: Diel observations of the impact of urban and biogenic Emissions) Messkampagne im August/September 2011 auf dem kleinen Feldberg in der Nähe von Frankfurt am Main wurde die Feldtauglichkeit des AIMS demonstriert. Die Nachweisgrenzen liegen für eine Mittelungszeit von 60 Minuten für Organik bei 1,4 µg m-3, für Nitrat bei 0,5 µg m-3 und für Sulfat bei 0,7 µg m-3, was ausreichend ist um atmosphärisches Aerosol messen zu können. Dies ist ein signifikanter Fortschritt im Vergleich zum Prototypen, der aufgrund schlechter Reproduzierbarkeit und Robustheit noch nicht feldtauglich war. Im Vergleich zum HR-ToF-AMS, einem Standard-Aerosolmassenspektrometer, zeigte sich, dass beide Instrumente vergleichbare Trends für die Spezies Nitrat, Sulfat und Organik messen.

New enhancement strategies for plasmon-enhanced fluorescence biosensors

This thesis investigates metallic nanostructures exhibiting surface plasmon resonance for the amplification of fluorescence signal in sandwich immunoassays. In this approach, an analyte is captured by an antibody immobilized on a plasmonic structure and detected by a subsequently bound fluorophore labeled detection antibody. The highly confined field of surface plasmons originates from collective charge oscillations which are associated with high electromagnetic field enhancements at the metal surface and allow for greatly increased fluorescence signal from the attached fluorophores. This feature allows for improving the signal-to-noise ratio in fluorescence measurements and thus advancing the sensitivity of the sensor platform. In particular, the thesis presents two plasmonic nanostructures that amplify fluorescence signal in devices that rely on epifluorescence geometry, in which the fluorophore absorbs and emits light from the same direction perpendicular to the substrate surface.rnThe first is a crossed relief gold grating that supports propagating surface plasmon polaritons (SPPs) and second, gold nanoparticles embedded in refractive index symmetric environment exhibiting collective localized surface plasmons (cLSPs). Finite-difference time-domain simulations are performed in order to design structures for the optimum amplification of established Cy5 and Alexa Fluor 647 fluorophore labels with the absorption and emission wavelengths in the red region of spectrum. The design takes into account combined effect of surface plasmon-enhanced excitation rate, directional surface plasmon-driven emission and modified quantum yield for characteristic distances in immunoassays. Homebuilt optical instruments are developed for the experimental observation of the surface plasmon mode spectrum, measurements of the angular distribution of surface plasmon-coupled fluorescence light and a setup mimicking commercial fluorescence reading systems in epifluorescence geometry.rnCrossed relief grating structures are prepared by interference lithography and multiple copies are made by UV nanoimprint lithography. The fabricated crossed diffraction gratings were utilized for sandwich immunoassay-based detection of the clinically relevant inflammation marker interleukin 6 (IL-6). The enhancement factor of the crossed grating reached EF=100 when compared to a flat gold substrate. This result is comparable to the highest reported enhancements to date, for fluorophores with relatively high intrinsic quantum yield. The measured enhancement factor excellently agrees with the predictions of the simulations and the mechanisms of the enhancement are explained in detail. Main contributions were the high electric field intensity enhancement (30-fold increase) and the directional fluorescence emission at (4-fold increase) compared to a flat gold substrate.rnCollective localized surface plasmons (cLSPs) hold potential for even stronger fluorescence enhancement of EF=1000, due to higher electric field intensity confinement. cLSPs are established by diffractive coupling of the localized surface plasmon resonance (LSPR) of metallic nanoparticles and result in a narrow resonance. Due to the narrow resonance, it is hard to overlap the cLSPs mode with the absorption and emission bands of the used fluorophore, simultaneously. Therefore, a novel two resonance structure that supports SPP and cLSP modes was proposed. It consists of a 2D array of cylindrical gold nanoparticles above a low refractive index polymer and a silver film. A structure that supports the proposed SPP and cLSP modes was prepared by employing laser interference lithography and the measured mode spectrum was compared to simulation results.rn

Performance evaluation of detector for digital radiography

Lo scopo di questo lavoro è la caratterizzazione fisica del flat panel PaxScan4030CB Varian, rivelatore di raggi X impiegato in un ampio spettro di applicazioni cliniche, dalla radiografia generale alla radiologia interventistica. Nell’ambito clinico, al fine di una diagnosi accurata, è necessario avere una buona qualità dell’immagine radiologica mantenendo il più basso livello di dose rilasciata al paziente. Elemento fondamentale per ottenere questo risultato è la scelta del rivelatore di radiazione X, che deve garantire prestazioni fisiche (contrasto, risoluzione spaziale e rumore) adeguati alla specifica procedura. Le metriche oggettive che misurano queste caratteristiche sono SNR (Signal-to-Noise Ratio), MTF (Modulation Transfer Function) ed NPS (Noise Power Spectrum), che insieme contribuiscono alla misura della DQE (Detective Quantum Efficiency), il parametro più completo e adatto a stabilire le performance di un sistema di imaging. L’oggettività di queste misure consente anche di mettere a confronto tra loro diversi sistemi di rivelazione. La misura di questi parametri deve essere effettuata seguendo precisi protocolli di fisica medica, che sono stati applicati al rivelatore PaxScan4030CB presente nel laboratorio del Centro di Coordinamento di Fisica Medica, Policlinico S.Orsola. I risultati ottenuti, conformi a quelli dichiarati dal costruttore, sono stati confrontati con successo con alcuni lavori presenti in letteratura e costituiscono la base necessaria per la verifica di procedure di ottimizzazione dell’immagine radiologica attraverso interventi sul processo di emissione dei raggi X e sul trattamento informatico dell’immagine (Digital Subtraction Angiography).

Performance analysis of reconstruction algorithms for breast microwave imaging

The problem of localizing a scatterer, which represents a tumor, in a homogeneous circular domain, which represents a breast, is addressed. A breast imaging method based on microwaves is considered. The microwave imaging involves to several techniques for detecting, localizing and characterizing tumors in breast tissues. In all such methods an electromagnetic inverse scattering problem exists. For the scattering detection method, an algorithm based on a linear procedure solution, inspired by MUltiple SIgnal Classification algorithm (MUSIC) and Time Reversal method (TR), is implemented. The algorithm returns a reconstructed image of the investigation domain in which it is detected the scatterer position. This image is called pseudospectrum. A preliminary performance analysis of the algorithm vying the working frequency is performed: the resolution and the signal-to-noise ratio of the pseudospectra are improved if a multi-frequency approach is considered. The Geometrical Mean-MUSIC algorithm (GM- MUSIC) is proposed as multi-frequency method. The performance of the GMMUSIC is tested in different real life computer simulations. The performed analysis shows that the algorithm detects the scatterer until the electrical parameters of the breast are known. This is an evident limit, since, in a real life situation, the anatomy of the breast is unknown. An improvement in GM-MUSIC is proposed: the Eye-GMMUSIC algorithm. Eye-GMMUSIC algorithm needs no a priori information on the electrical parameters of the breast. It is an optimizing algorithm based on the pattern search algorithm: it searches the breast parameters which minimize the Signal-to-Clutter Mean Ratio (SCMR) in the signal. Finally, the GM-MUSIC and the Eye-GMMUSIC algorithms are tested on a microwave breast cancer detection system consisting of an dipole antenna, a Vector Network Analyzer and a novel breast phantom built at University of Bologna. The reconstruction of the experimental data confirm the GM-MUSIC ability to localize a scatterer in a homogeneous medium.

Audiological results with Baha in conductive and mixed hearing loss

The level of improvement in the audiological results of Baha(®) users mainly depends on the patient's preoperative hearing thresholds and the type of Baha sound processor used. This investigation shows correlations between the preoperative hearing threshold and postoperative aided thresholds and audiological results in speech understanding in quiet of 84 Baha users with unilateral conductive hearing loss, bilateral conductive hearing loss and bilateral mixed hearing loss. Secondly, speech understanding in noise of 26 Baha users with different Baha sound processors (Compact, Divino, and BP100) is investigated. Linear regression between aided sound field thresholds and bone conduction (BC) thresholds of the better ear shows highest correlation coefficients and the steepest slope. Differences between better BC thresholds and aided sound field thresholds are smallest for mid-frequencies (1 and 2 kHz) and become larger at 0.5 and 4 kHz. For Baha users, the gain in speech recognition in quiet can be expected to lie in the order of magnitude of the gain in their hearing threshold. Compared to its predecessor sound processors Baha(®) Compact and Baha(®) Divino, Baha(®) BP100 improves speech understanding in noise significantly by +0.9 to +4.6 dB signal-to-noise ratio, depending on the setting and the use of directional microphone. For Baha users with unilateral and bilateral conductive hearing loss and bilateral mixed hearing loss, audiological results in aided sound field thresholds can be estimated with the better BC hearing threshold. The benefit in speech understanding in quiet can be expected to be similar to the gain in their sound field hearing threshold. The most recent technology of Baha sound processor improves speech understanding in noise by an order of magnitude that is well perceived by users and which can be very useful in everyday life.

Restricted or severely hindered diffusion of intramyocellular lipids in human skeletal muscle shown by in vivo proton MR spectroscopy

Although magnetic resonance spectroscopy can be used as a unique tool to study molecular diffusion, it is rarely used to measure the diffusion properties of intramyocellular and extramyocellular lipids. Lipids have very low apparent diffusion coefficients (ADCs), which make these measurements difficult and necessitate strong diffusion gradients and long diffusion times. Consequence is that these measurements have inherently low signal-to-noise ratio and are prone to artifacts. The addition of physiological triggering and individual storage and processing of the spectra is seen to be a possible approach to maximize signal intensity and achieve high reproducibility of the experiments. Thus, the optimized measurement protocol was used to investigate the diffusion properties of lipids in human skeletal muscle in vivo. At a diffusion time of about 110 ms, intramyocellular lipids show a significantly lower ADC (2.0 × 10(-6) mm(2)/s, 95% confidence interval 1.10 × 10(-6) to 2.94 × 10(-6) mm(2)/s) than extramyocellular lipids (1.58 × 10(-5) mm(2)/s, 95% confidence interval 1.41 × 10(-5) to 1.75 × 10(-5) mm(2)/s). Because the chemical properties of both lipid pools can be assumed to be similar, the difference can only be attributed to restricted or severely hindered diffusion in the intramyocellular droplets.

A 20-channel receive-only mouse array coil for a 3 T clinical MRI system

A 20-channel phased-array coil for MRI of mice has been designed, constructed, and validated with bench measurements and high-resolution accelerated imaging. The technical challenges of designing a small, high density array have been overcome using individual small-diameter coil elements arranged on a cylinder in a hexagonal overlapping design with adjacent low impedance preamplifiers to further decouple the array elements. Signal-to-noise ratio (SNR) and noise amplification in accelerated imaging were simulated and quantitatively evaluated in phantoms and in vivo mouse images. Comparison between the 20-channel mouse array and a length-matched quadrature driven small animal birdcage coil showed an SNR increase at the periphery and in the center of the phantom of 3- and 1.3-fold, respectively. Comparison with a shorter but SNR-optimized birdcage coil (aspect ratio 1:1 and only half mouse coverage) showed an SNR gain of twofold at the edge of the phantom and similar SNR in the center. G-factor measurements indicate that the coil is well suited to acquire highly accelerated images.

Non-water-suppressed proton MR spectroscopy improves spectral quality in the human spinal cord

Magnetic resonance spectroscopy enables insight into the chemical composition of spinal cord tissue. However, spinal cord magnetic resonance spectroscopy has rarely been applied in clinical work due to technical challenges, including strong susceptibility changes in the region and the small cord diameter, which distort the lineshape and limit the attainable signal to noise ratio. Hence, extensive signal averaging is required, which increases the likelihood of static magnetic field changes caused by subject motion (respiration, swallowing), cord motion, and scanner-induced frequency drift. To avoid incoherent signal averaging, it would be ideal to perform frequency alignment of individual free induction decays before averaging. Unfortunately, this is not possible due to the low signal to noise ratio of the metabolite peaks. In this article, frequency alignment of individual free induction decays is demonstrated to improve spectral quality by using the high signal to noise ratio water peak from non-water-suppressed proton magnetic resonance spectroscopy via the metabolite cycling technique. Electrocardiography (ECG)-triggered point resolved spectroscopy (PRESS) localization was used for data acquisition with metabolite cycling or water suppression for comparison. A significant improvement in the signal to noise ratio and decrease of the Cramér Rao lower bounds of all metabolites is attained by using metabolite cycling together with frequency alignment, as compared to water-suppressed spectra, in 13 healthy volunteers.

Pros and cons of low-field magnetic resonance imaging in veterinary practice

Low-field (LF) (0.2-0.4T) magnetic resonance (MR) imaging predominates in veterinary practice. Advantages of LF MR include reduced costs, better patient access, and greater safety. High quality examinations can be achieved using appropriate protocols and investing more scanning time than with high-field (HF) systems. The main disadvantage of LF MR is the reduced signal to noise ratio compared with HF systems. LF MR protocols for small animal brain and spine imaging are described.

Esophageal ECG: The challenge of electrode design

Two commercially available electrode catheters are examined for their suitability in esophageal long-term ECG recordings. Both, electrical sensing characteristics as well as clinical acceptance were investigated in a clinical study including inpatients with cardiovascular diseases. In total, 31 esophageal ECG were obtained in 36 patients. Results showed that esophageal electrodes were well tolerated by the patients. Hemispherical electrodes with higher diameter required more insertion attempts and were associated with increased failure rates as compared to cylindrical electrodes. In contrast, the higher surface area of hemispherical electrodes resulted in significantly higher signal-to-noise ratio. Contact impedance was equal for both electrode types, but esophageal electrodes had lower impedance if compared with skin electrodes.

Graph-Based Multi-Surface Segmentation of OCT Data Using Trained Hard and Soft Constraints

Optical coherence tomography (OCT) is a well-established image modality in ophthalmology and used daily in the clinic. Automatic evaluation of such datasets requires an accurate segmentation of the retinal cell layers. However, due to the naturally low signal to noise ratio and the resulting bad image quality, this task remains challenging. We propose an automatic graph-based multi-surface segmentation algorithm that internally uses soft constraints to add prior information from a learned model. This improves the accuracy of the segmentation and increase the robustness to noise. Furthermore, we show that the graph size can be greatly reduced by applying a smart segmentation scheme. This allows the segmentation to be computed in seconds instead of minutes, without deteriorating the segmentation accuracy, making it ideal for a clinical setup. An extensive evaluation on 20 OCT datasets of healthy eyes was performed and showed a mean unsigned segmentation error of 3.05 ±0.54 μm over all datasets when compared to the average observer, which is lower than the inter-observer variability. Similar performance was measured for the task of drusen segmentation, demonstrating the usefulness of using soft constraints as a tool to deal with pathologies.

Enhancing Sensitivity In Natural Product Nmr: Exploring Optimal Non-Uniform Sampling

Recent optimizations of NMR spectroscopy have focused their attention on innovations in new hardware, such as novel probes and higher field strengths. Only recently has the potential to enhance the sensitivity of NMR through data acquisition strategies been investigated. This thesis has focused on the practice of enhancing the signal-to-noise ratio (SNR) of NMR using non-uniform sampling (NUS). After first establishing the concept and exact theory of compounding sensitivity enhancements in multiple non-uniformly sampled indirect dimensions, a new result was derived that NUS enhances both SNR and resolution at any given signal evolution time. In contrast, uniform sampling alternately optimizes SNR (t < 1.26T2) or resolution (t~3T2), each at the expense of the other. Experiments were designed and conducted on a plant natural product to explore this behavior of NUS in which the SNR and resolution continue to improve as acquisition time increases. Possible absolute sensitivity improvements of 1.5 and 1.9 are possible in each indirect dimension for matched and 2x biased exponentially decaying sampling densities, respectively, at an acquisition time of ¿T2. Recommendations for breaking into the linear regime of maximum entropy (MaxEnt) are proposed. Furthermore, examination into a novel sinusoidal sampling density resulted in improved line shapes in MaxEnt reconstructions of NUS data and comparable enhancement to a matched exponential sampling density. The Absolute Sample Sensitivity derived and demonstrated here for NUS holds great promise in expanding the adoption of non-uniform sampling.

Fiberoptic system for recording dendritic calcium signals in layer 5 neocortical pyramidal cells in freely moving rats

Calcium influx into the dendritic tufts of layer 5 neocortical pyramidal neurons modifies a number of important cellular mechanisms. It can trigger local synaptic plasticity and switch the firing properties from regular to burst firing. Due to methodological limitations, our knowledge about Ca2+ spikes in the dendritic tuft stems mostly from in vitro experiments. However, it has been speculated that regenerative Ca2+ events in the distal dendrites correlate with distinct behavioral states. Therefore it would be most desirable to be able to record these Ca2+ events in vivo, preferably in the behaving animal. Here, we present a novel approach for recording Ca2+ signals in the dendrites of populations of layer 5 pyramidal neurons in vivo, which ensures that all recorded fluorescence changes are due to intracellular Ca2+ signals in the apical dendrites. The method has two main features: 1) bolus loading of layer 5 with a membrane-permeant Ca2+ dye resulting in specific loading of pyramidal cell dendrites in the upper layers and 2) a fiberoptic cable attached to a gradient index lens and a prism reflecting light horizontally at 90 degrees to the angle of the apical dendrites. We demonstrate that the in vivo signal-to-noise ratio recorded with this relatively inexpensive and easy-to-implement fiberoptic-based device is comparable to conventional camera-based imaging systems used in vitro. In addition, the device is flexible and lightweight and can be used for recording Ca2+ signals in the distal dendritic tuft of freely behaving animals.

Evaluation of magnetic resonance colonography at 3.0 Tesla regarding diagnostic accuracy and image quality

OBJECTIVES: To assess magnetic resonance (MR)-colonography (MRC) for detection of colorectal lesions using two different T1w three-dimensional (3D)-gradient-recalled echo (GRE)-sequences and integrated parallel data acquisition (iPAT) at a 3.0 Tesla MR-unit. MATERIALS AND METHODS: In this prospective study, 34 symptomatic patients underwent dark lumen MRC at a 3.0 Tesla unit before conventional colonoscopy (CC). After colon distension with tap water, 2 high-resolution T1w 3D-GRE [3-dimensional fast low angle shot (3D-FLASH), iPAT factor 2 and 3D-volumetric interpolated breathhold examination (VIBE), iPAT 3] sequences were acquired without and after bolus injection of gadolinium. Prospective evaluation of MRC was performed. Image quality of the different sequences was assessed qualitatively and quantitatively. The findings of the same day CC served as standard of reference. RESULTS: MRC identified all polyps >5 mm (16 of 16) in size and all carcinomas (4 of 4) correctly. Fifty percent of the small polyps signal-to-noise ratio (8 +/- 3.3 standard deviation (SD) in lesions without contrast enhancement (CE); 24.3 +/- 7.8 SD after CE). For the 3D-VIBE sequence, signal-to-noise ratio doubled in the detected lesions (147 +/- 54 SD without and 292 +/- 168 SD after CE). Although image quality was ranked lower in the VIBE, the image quality score of both sequences showed no statistical significant difference (chi > 0.6). CONCLUSIONS: MRC using 3D-GRE-sequences and iPAT is feasible at 3.0 T-systems. The high-resolution 3D-FLASH was slightly preferred over the 3D-VIBE because of better image quality, although both used sequences showed no statistical significant difference.