Performance and reproducibility of 13C and 15N hyperpolarization using a cryogen-free DNP polarizer

The setup, operational procedures and performance of a cryogen-free device for producing hyperpolarized contrast agents using dissolution dynamic nuclear polarization (dDNP) in a preclinical imaging center is described. The polarization was optimized using the solid-state, DNP-enhanced NMR signal to calibrate the sample position, microwave and NMR frequency and power and flip angle. The polarization of a standard formulation to yield ~ 4 mL, 60 mM 1-13C-pyruvic acid in an aqueous solution was quantified in five experiments to P(13C) = (38 ± 6) % (19 ± 1) s after dissolution. The mono-exponential time constant of the build-up of the solid-state polarization was quantified to (1032 ± 22) s. We achieved a duty cycle of 1.5 h that includes sample loading, monitoring the polarization build-up, dissolution and preparation for the next run. After injection of the contrast agent in vivo, pyruvate, pyruvate hydrate, lactate, and alanine were observed, by measuring metabolite maps. Based on this work sequence, hyperpolarized 15N urea was obtained (P(15N) = (5.6 ± 0.8) % (30 ± 3) s after dissolution)

Imaging Inflammation - From Whole Body Imaging to Cellular Resolution

Imaging techniques have evolved impressively lately, allowing whole new concepts like multimodal imaging, personal medicine, theranostic therapies, and molecular imaging to increase general awareness of possiblities of imaging to medicine field. Here, we have collected the selected (3D) imaging modalities and evaluated the recent findings on preclinical and clinical inflammation imaging. The focus has been on the feasibility of imaging to aid in inflammation precision medicine, and the key challenges and opportunities of the imaging modalities are presented. Some examples of the current usage in clinics/close to clinics have been brought out as an example. This review evaluates the future prospects of the imaging technologies for clinical applications in precision medicine from the pre-clinical development point of view

Structural and optical properties of short period superlattices for rational (In,Ga)N

In dieser Arbeit untersuchen wir ultradünne (In,Ga)N Quantentöpfe (QW) in Form von kurzperiodischen Übergittern auf (0001) GaN. Wir charakterisieren dieser Strukturen mit verschiedenen Methoden, d.h.: die hochauflösende Transmissionselektronenmikroskopie, die Rastertransmissionselektronenmikroskopie, Röntgenbeugung und die hochenergetischer Refeflexionselektronenbeugung an Oberflächen, sowie die Photolumineszenz (PL) und die Kathodolumineszenz. Wir fokussieren uns dabei auf die Quantifizierung des Indiumgehaltes solche ultradünnen Schichten und diskutieren über grundlegende optische Eigenschaften dieser Übergitter. Wir finden, dass: 1. Der Indiumeinbau in GaN unter Exposition von In und N-Fluss ist selbst-begrenzend auf eine Zusammensetzung von 25% und eine Schichtdicke von einer Monolage. Die Variation der Wachstumsbedingungen führen weder nicht zu einer Höhung des Indiumgehalts noch der Schichtdicke. Diese Selbstbegrenzung ist im Ergebnis auf die Unterschiede in der Bildungsenthalpie von InN und GaN und auf die hohe Gitterfehlanpassung des Systems. Die niedrigste Energiekonfiguration ist einer (2»3×2»3)R30° Oberflächenrekonstruktion. 2. In diesen polaren In0.25Ga0.75N Übergitter Polarisationsfelder, Dickenfluktuationen oder Kompositionsschwankungen keine wesentliche Rolle spielen. Unsere optischen Studien in Kombination mit DFT-Berechnungen zeigen, dass der Rekombinationsprozess durch den Einschluss der Lochwellenfunktion in den Monoschichten gesteuert wird, dass mit abnehmender Barrieredicke verändert werden können. Im Gegenteil, ist die Elektronenwellenfunktion immer delokalisiert. Unsere Übergitter Phänomene sind als in konventionellen QWs, z.B. den nichtexponentiellen Abfall der PL-Intensität, die spektrale Abhängigkeit der PL Lebensdauer und eine S-förmige Temperaturabhängigkeit des Emissionspeaks. Die letzte lassen sich durch das Zusammenspiel von Ladunsgträgerlokalisation und nicht-strahliger Rekombination erklären.In this work we investigate ultra-thin (In,Ga)N quantum wells (QWs) grown on (0001) GaN in the form of short-period superlattices (SLs). We perform a comprehensive study of these structures via various methods, i.e.: high resolution transmission electron microscopy, scanning transmission electron microscopy, x-ray diffraction and reflection high-energy electron diffraction, as well as photoluminescence (PL) and cathodoluminescence. We focus on the quantification of In incorporation and study basic optical properties of these SLs. The main results of our investigations are: 1. The In incorporation into GaN under exposure of In and N flux is self-limited to a composition of 25% and a layer thickness of one monolayer. Varying growth conditions do not increase the In content or the layer thickness. This self-limitation is a result of the differences in formation enthalpy of InN and GaN and the high lattice mismatch of the system. The lowest energy configuration that sets maximum In concentration to a fundamental limit of 25%, stable under various growth regimes, is the one with (2»3×2»3)R30° surface reconstruction. 2. Our polar In0.25Ga0.75N SLs serve as model system for recombination process in (In,Ga)N since their recombination is not suffering from polarization fields, well-width or high compositional fluctuations. The optical studies combined with DFT calculations show that the recombination process is governed by the confinement of the hole wavefunction in the QWs, that can be substantially weakened by decreasing barrier thickness. This leads to an increase of non-radiative recombination in the barriers. In the opposite, the electron wave function is always delocalized. Our SLs show common phenomena observed in conventional QWs or bulk alloys like a non-exponential decay of the PL intensity, spectral dependence of the decay time and S-shape temperature dependence. The latter can be explained by the interplay of carrier localization and non-radiative recombination