Hyperpolarization without persistent radicals for in vivo real-time metabolic imaging

Abstract

Hyperpolarized substrates prepared via dissolution dynamic nuclear polarization have been proposed as magnetic resonance imaging (MRI) agents for cancer or cardiac failure diagnosis and therapy monitoring through the detection of metabolic impairments in vivo. The use of potentially toxic persistent radicals to hyperpolarize substrates was hitherto required. We demonstrate that by shining UV light for an hour on a frozen pure endogenous substance, namely the glucose metabolic product pyruvic acid, it is possible to generate a concentration of photo-induced radicals that is large enough to highly enhance the 13 C polarization of the substance via dynamic nuclear polarization. These radicals recombine upon dissolution and a solution composed of purely endogenous products is obtained for performing in vivo metabolic hyperpolarized 13 C MRI with high spatial resolution. Our method opens the way to safe and straightforward preclinical and clinical applications of hyperpolarized MRI because the filtering procedure mandatory for clinical applications and the associated pharmacological tests necessary to prevent contamination are eliminated, concurrently allowing a decrease in the delay between preparation and injection of the imaging agents for improved in vivo sensitivity.is a very powerful imaging modality in terms of temporal and spatial resolution of anatomical structures. The modality is widespread, well established in clinical environments, and paramagnetic agents are used extensively for enhanced contrast or perfusion examination. MR is also a unique technique to obtain in vivo metabolic maps using the spectroscopic information that can be extracted from the time-domain acquisitions. In particular, it is possible to monitor the biochemical transformations of specific substrates that are delivered to subjects. Because it gives access to the kinetics of the conversion of substrates into metabolites, MR spectroscopy (MRS) of the carbon nuclei ( 13 C) is one of the most powerful techniques to investigate intermediary metabolism (1).The well-known weakness of MR as a spectroscopic technique is its relatively low sensitivity. It can be offset by so-called hyperpolarization methods, in particular the one based on dynamic nuclear polarization (DNP) (2), which is now commonly referred to as dissolution DNP and was first proposed about a decade ago (3). The hyperpolarized substrates obtained following dissolution DNP are biomolecules in aqueous solution with a largely out-ofequilibrium nuclear spin polarization corresponding to an enhancement of several orders of magnitude compared with the thermal equilibrium polarization attainable in MRI scanners. A basic requirement for DNP is the presence of unpaired electron spins in the sample to be hyperpolarized. These polarizing agents are usually incorporated in the form of persistent radicals. An inherent limit of any hyperpolarization method is that the intrinsic longitudinal nuclear spin relaxation will annihilate the polarization enhancement in the course of time to reach t...

Optimal Glass-Forming Solvent Brings Sublimation Dynamic Nuclear Polarization to 129Xe Hyperpolarization Biomedical Imaging Standards

“…trityl radicals or UV induced radicals). 39 Replacing natural xenon by 129 Xe-enriched 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 …”

Michel Borghini as a Mentor and Father of the Theory of Polarization in Polarized Targets

“…25 for a recent development and references therein. The medical people call this hyperpolarization, but the polarization happens in setups similar to the ones used in polarized targets, see e.g.. 26 The surprising discovery: after thawing the samples in a magnetic field, the polarization is largely maintained in the gas phase. Dissolving the gas into a liquid and injecting it into the body yields strongly enhanced NMR signals of the tumors.…”

Persistent Radicals of Self‐assembled Benzophenone bis‐Urea Macrocycles: Characterization and Application as a Polarizing Agent for Solid‐state DNP MAS Spectroscopy

“…9,10 Instead, the quasi-stable, short-lived UV-induced radicals were shown to afford sizeable DNP enhancements at low temperatures. 9, 10 Larger DNP enhancements are possible in solution and have been observed in frozen media under constant irradiation (photochemically induced DNP). 11 With exogenous radicals, optimum concentration is key, as high radical concentration can result in excessive paramagnetic relaxation and line broadening.…”

“…4, 12 Few studies have examined DNP using endogenous radicals in the solid-state or single crystals. 5, 9, 10 …”