Design and performance of a DNP prepolarizer coupled to a rodent MRI scanner

For most of the last forty years, the techniques of Dynamic Nuclear Polarization (DNP) have been confined to particle-physics laboratories building polarized targets, but recently it has been shown that samples similar to a solid target can be transformed into room temperature liquid solutions while retaining a high nuclear polarization. This method of "hyperpolarization" is of interest in NMR/MRI/MRS. We describe a 3.35 T DNP/9.4 T MRI installation based on a continuous-flow cryostat, using a standard wide-bore low-field NMR magnet as prepolarizer magnet and a widely available radical as polarizing agent. The interfacing to a rodent scanner requires that the infusion of the polarized solution in the animal be remotely controlled, because of limited access inside the magnet bore. Physiological constraints on the infusion rate can be a serious source of polarization loss, and the discussion of efficiency is therefore limited to that of the prepolarizer itself, i.e., the spin temperatures obtained in the solid state. To put our results in context, we summarize data obtained in targets with different types of radicals, and provide a short review of the DNP mechanisms needed in their discussion. (C) 2007 Wiley Periodicals, Inc

CdTe solar cells in a novel configuration

Polycrystalline thin-film CdTe/CdS solar cells have been developed in a configuration in which a transparent conducting layer of indium tin oxide (ITO) has been used for the first time as a back electrical contact on p-CdTe. Solar cells of 7.9% efficiency were developed on SnOx:F-coated glass substrates with a low-temperature (<450\ub0C) high-vacuum evaporation method. After the CdCl2 annealing treatment of the CdTe/CdS stack, a bromine methanol solution was used for etching the CdTe surface prior to the ITO deposition. The unique features of this solar cell with both front and back contacts being transparent and conducting are that the cell can be illuminated from either or both sides simultaneously like a 'bi-facial' cell, and it can be used in tandem solar cells. The solar cells with transparent conducting oxide back contact show long-term stable performance under accelerated test conditions

Dynamic nuclear polarization of small labelled molecules in frozen water-alcohol solutions

In recent years methods of creating 'hyperpolarized' substances have gained considerable attention in biomedical magnetic resonance and dynamic nuclear polarization (DNP) is one of the most promising, especially for imaging applications. Here we present results of DNP studies on protons and C-13 nuclei in frozen solutions of sodium acetate and glycine, dissolved in water-ethanol and water-glycerol, doped with TEMPO free radicals and EHBA-Cr-V complexes. Up to 14% C-13 polarization and close to 50% proton polarization were achieved at similar to 1.2K in a magnetic field of similar to 3.5 T under irradiation with similar to 97 GHz microwaves, which corresponds to an enhancement of more than 15 000 with respect to thermal equilibrium polarization in a 9.4 T magnet at room temperature. For all investigated samples the main DNP mechanism was found to be thermal mixing. The absolute polarization values achieved are mainly depending on the type of solvent, the water-alcohol ratio, its degree of deuteration and the concentration of paramagnetic centres. This allows application of the so-established sample preparation and DNP procedure to other molecules in future experiments. Two further examples of DNP of molecules in solution underline the general applicability of the method to a wide variety of organic compounds

A 140 GHz prepolarizer for dissolution dynamic nuclear polarization

Apart from their very classical use to build polarized targets for particle physics, the methods of dynamic nuclear polarization (DNP) have more recently found application for sensitivity enhancement in high-resolution NMR, both in the solid and in the liquid state. It is often thought that the possible signal enhancement in such applications deteriorates when the DNP is performed at higher fields. We show that for a dissolution-DNP method that uses conventional (2,2,6,6-tetramethylpiperidine 1-oxyl) radicals as the paramagnetic agent, this is not the case for fields up to 5 T. (C) 2008 American Institute of Physics

Producing over 100 ml of highly concentrated hyperpolarized solution by means of dissolution DNP

New low-temperature inserts compatible with an existing hyperpolarizer were developed to dynamically polarize nuclei in large samples. The performance of the system was tested on 8 ml glassy frozen solutions containing 13C-labeled molecules and doped with nitroxyl free radicals. The obtained 13C low-temperature polarization was comparable to the one measured on 20 times smaller sample volume with only 3-4 times higher microwave power. By using a dissolution insert that fits to the new design, it was possible to obtain about 120 ml of room-temperature hyperpolarized solution. The polarization as well as the molecule concentration was comparable to the values obtained in standard size hyperpolarized samples. Such large samples are interesting for future studies on larger animals and possibly for potential clinical applications. © 2008 Elsevier Inc. All rights reserved