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      The Feasibility of Formation and Kinetics of NMR Signal Amplification by Reversible Exchange (SABRE) at High Magnetic Field (9.4 T)

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          Abstract

          1H NMR signal amplification by reversible exchange (SABRE) was observed for pyridine and pyridine- d 5 at 9.4 T, a field that is orders of magnitude higher than what is typically utilized to achieve the conventional low-field SABRE effect. In addition to emissive peaks for the hydrogen spins at the ortho positions of the pyridine substrate (both free and bound to the metal center), absorptive signals are observed from hyperpolarized orthohydrogen and Ir-complex dihydride. Real-time kinetics studies show that the polarization build-up rates for these three species are in close agreement with their respective 1H T 1 relaxation rates at 9.4 T. The results suggest that the mechanism of the substrate polarization involves cross-relaxation with hyperpolarized species in a manner similar to the spin-polarization induced nuclear Overhauser effect. Experiments utilizing pyridine- d 5 as the substrate exhibited larger enhancements as well as partial H/D exchange for the hydrogen atom in the ortho position of pyridine and concomitant formation of HD molecules. While the mechanism of polarization enhancement does not explicitly require chemical exchange of hydrogen atoms of parahydrogen and the substrate, the partial chemical modification of the substrate via hydrogen exchange means that SABRE under these conditions cannot rigorously be referred to as a non-hydrogenative parahydrogen induced polarization process.

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          Most cited references17

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          Increase in signal-to-noise ratio of > 10,000 times in liquid-state NMR.

          A method for obtaining strongly polarized nuclear spins in solution has been developed. The method uses low temperature, high magnetic field, and dynamic nuclear polarization (DNP) to strongly polarize nuclear spins in the solid state. The solid sample is subsequently dissolved rapidly in a suitable solvent to create a solution of molecules with hyperpolarized nuclear spins. The polarization is performed in a DNP polarizer, consisting of a super-conducting magnet (3.35 T) and a liquid-helium cooled sample space. The sample is irradiated with microwaves at approximately 94 GHz. Subsequent to polarization, the sample is dissolved by an injection system inside the DNP magnet. The dissolution process effectively preserves the nuclear polarization. The resulting hyperpolarized liquid sample can be transferred to a high-resolution NMR spectrometer, where an enhanced NMR signal can be acquired, or it may be used as an agent for in vivo imaging or spectroscopy. In this article we describe the use of the method on aqueous solutions of [13C]urea. Polarizations of 37% for 13C and 7.8% for 15N, respectively, were obtained after the dissolution. These polarizations correspond to an enhancement of 44,400 for 13C and 23,500 for 15N, respectively, compared with thermal equilibrium at 9.4 T and room temperature. The method can be used generally for signal enhancement and reduction of measurement time in liquid-state NMR and opens up for a variety of in vitro and in vivo applications of DNP-enhanced NMR.
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            Detecting tumor response to treatment using hyperpolarized 13C magnetic resonance imaging and spectroscopy.

            Measurements of early tumor responses to therapy have been shown, in some cases, to predict treatment outcome. We show in lymphoma-bearing mice injected intravenously with hyperpolarized [1-(13)C]pyruvate that the lactate dehydrogenase-catalyzed flux of (13)C label between the carboxyl groups of pyruvate and lactate in the tumor can be measured using (13)C magnetic resonance spectroscopy and spectroscopic imaging, and that this flux is inhibited within 24 h of chemotherapy. The reduction in the measured flux after drug treatment and the induction of tumor cell death can be explained by loss of the coenzyme NAD(H) and decreases in concentrations of lactate and enzyme in the tumors. The technique could provide a new way to assess tumor responses to treatment in the clinic.
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              Analysis of cancer metabolism by imaging hyperpolarized nuclei: prospects for translation to clinical research.

              A major challenge in cancer biology is to monitor and understand cancer metabolism in vivo with the goal of improved diagnosis and perhaps therapy. Because of the complexity of biochemical pathways, tracer methods are required for detecting specific enzyme-catalyzed reactions. Stable isotopes such as (13)C or (15)N with detection by nuclear magnetic resonance provide the necessary information about tissue biochemistry, but the crucial metabolites are present in low concentration and therefore are beyond the detection threshold of traditional magnetic resonance methods. A solution is to improve sensitivity by a factor of 10,000 or more by temporarily redistributing the populations of nuclear spins in a magnetic field, a process termed hyperpolarization. Although this effect is short-lived, hyperpolarized molecules can be generated in an aqueous solution and infused in vivo where metabolism generates products that can be imaged. This discovery lifts the primary constraint on magnetic resonance imaging for monitoring metabolism-poor sensitivity-while preserving the advantage of biochemical information. The purpose of this report was to briefly summarize the known abnormalities in cancer metabolism, the value and limitations of current imaging methods for metabolism, and the principles of hyperpolarization. Recent preclinical applications are described. Hyperpolarization technology is still in its infancy, and current polarizer equipment and methods are suboptimal. Nevertheless, there are no fundamental barriers to rapid translation of this exciting technology to clinical research and perhaps clinical care.
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                Author and article information

                Journal
                J Am Chem Soc
                J. Am. Chem. Soc
                ja
                jacsat
                Journal of the American Chemical Society
                American Chemical Society
                0002-7863
                1520-5126
                14 February 2015
                14 February 2014
                05 March 2014
                : 136
                : 9
                : 3322-3325
                Affiliations
                [1] International Tomography Center, Novosibirsk State University, Novosibirsk 630090, Russia
                [3] §Institute of Imaging Science, Department of Radiology, Department of Biomedical Engineering, Department of Physics and Astronomy, #Department of Biochemistry, Vanderbilt University , Nashville, Tennessee, 37232-2310, United States
                []Department of Chemistry and Biochemistry, Southern Illinois University , Carbondale, Illinois 62901, United States
                Author notes
                Article
                10.1021/ja501052p
                3985893
                24528143
                41263172-b688-4d93-b0bc-acb0850925df
                Copyright © 2014 American Chemical Society
                History
                : 15 November 2013
                Funding
                National Institutes of Health, United States
                Categories
                Communication
                Custom metadata
                ja501052p
                ja-2014-01052p

                Chemistry
                Chemistry

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