Dissolution Dynamic Nuclear Polarization capability study with fluid path

Enhanced Solubility and Polarization of 13C-Fumarate with Meglumine Allows for In Vivo Detection of Gluconeogenic Metabolism in Kidneys

Hyperpolarized 13C-labeled fumarate probes tissue necrosis via the production of 13C-malate. Despite its promises in detecting tumor necrosis and kidney injuries, its clinical translation has been limited, primarily due to the low solubility in conventional glassing solvents. In this study, we introduce a new formulation of fumarate for dissolution dynamic nuclear polarization (DNP) by using meglumine as a counterion, a nonmetabolizable derivative of sorbitol. We have found that meglumine fumarate vitrifies by itself with enhanced water solubility (4.8 M), which is expected to overcome the solubility-restricted maximum concentration of hyperpolarized fumarate after dissolution. The achievable liquid-state polarization level of meglumine-fumarate is more than doubled (29.4 ± 1.3%) as compared to conventional dimethyl sulfoxide (DMSO)-mixed fumarate (13.5 ± 2.4%). In vivo comparison of DMSO- and meglumine-prepared 50-mM hyperpolarized [1,4-13C2]fumarate shows that the signal sensitivity in rat kidneys increases by 10-fold. As a result, [1,4-13C2]aspartate and [13C]bicarbonate in addition to [1,4-13C2]malate can be detected in healthy rat kidneys in vivo using hyperpolarized meglumine [1,4-13C2]fumarate. In particular, the appearance of [13C]bicarbonate indicates that hyperpolarized meglumine [1,4-13C2]fumarate can be used to investigate phosphoenolpyruvate carboxykinase, a key regulatory enzyme in gluconeogenesis.

Parahydrogen-Polarized [1-13 C]Pyruvate for Reliable and Fast Preclinical Metabolic Magnetic Resonance Imaging

Hyperpolarization techniques increase nuclear spin polarization by more than four orders of magnitude, enabling metabolic MRI. Even though hyperpolarization has shown clear value in clinical studies, the complexity, cost and slowness of current equipment limits its widespread use. Here, a polarization procedure of [1-13 C]pyruvate based on parahydrogen-induced polarization by side-arm hydrogenation (PHIP-SAH) in an automated polarizer is demonstrated. It is benchmarked in a study with 48 animals against a commercial dissolution dynamic nuclear polarization (d-DNP) device. Purified, concentrated (≈70-160 mM) and highly hyperpolarized (≈18%) solutions of pyruvate are obtained at physiological pH for volumes up to 2 mL within 85 s in an automated process. The safety profile, image quality, as well as the quantitative perfusion and lactate-to-pyruvate ratios, are equivalent for PHIP and d-DNP, rendering PHIP a viable alternative to established hyperpolarization techniques.

Practical dissolution dynamic nuclear polarization

This review article intends to provide insightful advice for dissolution-dynamic nuclear polarization in the form of a practical handbook. The goal is to aid research groups to effectively perform such experiments in their own laboratories. Previous review articles on this subject have covered a large number of useful topics including instrumentation, experimentation, theory, etc. The topics to be addressed here will include tips for sample preparation and for checking sample health; a checklist to correctly diagnose system faults and perform general maintenance; the necessary mechanical requirements regarding sample dissolution; and aids for accurate, fast and reliable polarization quantification. Herein, the challenges and limitations of each stage of a typical dissolution-dynamic nuclear polarization experiment are presented, with the focus being on how to quickly and simply overcome some of the limitations often encountered in the laboratory.

A novel sample handling system for dissolution dynamic nuclear polarization experiments

We present a system for facilitated sample vitrification, melting, and transfer in dissolution dynamic nuclear polarization (DDNP) experiments. In DDNP, a sample is typically hyperpolarized at cryogenic temperatures before dissolution with hot solvent and transfer to a nuclear magnetic resonance (NMR) spectrometer for detection in the liquid state. The resulting signal enhancements can exceed 4 orders of magnitude. However, the sudden temperature jump from cryogenic temperatures close to 1 K to ambient conditions imposes a particular challenge. It is necessary to rapidly melt the sample to avoid a prohibitively fast decay of hyperpolarization. Here, we demonstrate a sample dissolution method that facilitates the temperature jump by eliminating the need to open the cryostat used to cool the sample. This is achieved by inserting the sample through an airlock in combination with a dedicated dissolution system that is inserted through the same airlock shortly before the melting event. The advantages are threefold: (1) the cryostat can be operated continuously at low temperatures. (2) The melting process is rapid as no pressurization steps of the cryostat are required. (3) Blockages of the dissolution system due to freezing of solvents during melting and transfer are minimized.

Hyperpolarized MR - What's up Doc?

Hyperpolarized MR by dissolution Dynamic Nuclear Polarization (dDNP) appeared on the scene in 2003. Since then, it has been translated to the clinic and several sites are now conducting human studies. This has happened at record pace despite all its complexities. The method has reached a pivotal point, and the coming years will be critical in realizing its full potential. Though the field has been characterized by strong collaboration between academia, government and industry, the key message of this perspective paper is that accelerated consensus building is of the essence in fulfilling the original vision for the method and ensuring widespread adoption. The challenge is to gain acceptance among clinicians based on strong indications and clear evidence. The future appears bright; initial clinical data looks promising and the scope for improvement is significant.

Cryogen-free dissolution dynamic nuclear polarization polarizer operating at 3.35 T, 6.70 T, and 10.1 T

PURPOSE

A novel dissolution dynamic nuclear polarization (dDNP) polarizer platform is presented. The polarizer meets a number of key requirements for in vitro, preclinical, and clinical applications.

METHOD

It uses no liquid cryogens, operates in continuous mode, accommodates a wide range of sample sizes up to and including those required for human studies, and is fully automated.

RESULTS

It offers a wide operational window both in terms of magnetic field, up to 10.1 T, and temperature, from room temperature down to 1.3 K. The polarizer delivers a ¹³ C liquid state polarization for [1-¹³ C]pyruvate of 70%. The build-up time constant in the solid state is approximately 1200 s (20 minutes), allowing a sample throughput of at least one sample per hour including sample loading and dissolution.

CONCLUSION

We confirm the previously reported strong field dependence in the range 3.35 to 6.7 T, but see no further increase in polarization when increasing the magnetic field strength to 10.1 T for [1-¹³ C]pyruvate and trityl. Using a custom dry magnet, cold head and recondensing, closed-cycle cooling system, combined with a modular DNP probe, and automation and fluid handling systems, we have designed a unique dDNP system with unrivalled flexibility and performance.

Simultaneous imaging of hyperpolarized [1,4-13 C2 ]fumarate, [1-13 C]pyruvate and 18 F-FDG in a rat model of necrosis in a clinical PET/MR scanner

A co-polarization scheme for [1,4-¹³ C₂ ]fumarate and [1-¹³ C]pyruvate is presented to simultaneously assess necrosis and metabolism in rats with hyperpolarized ¹³ C magnetic resonance (MR). The co-polarization was performed in a SPINlab polarizer. In addition, the feasibility of simultaneous positron emission tomography (PET) and MR of small animals with a clinical PET/MR scanner is demonstrated. The hyperpolarized metabolic MR and PET was demonstrated in a rat model of necrosis. The polarization and T₁ of the co-polarized [1,4-¹³ C₂ ]fumarate and [1-¹³ C]pyruvate substrates were measured in vitro and compared with those obtained when the substrates were polarized individually. A polarization of 36 ± 4% for fumarate and 37 ± 6% for pyruvate was obtained. We found no significant difference in the polarization and T₁ values between the dual and single substrate polarization. Rats weighing about 400 g were injected intramuscularly in one of the hind legs with 200 μL of turpentine to induce necrosis. Two hours later, ¹³ C metabolic maps were obtained with a chemical shift imaging sequence (16 × 16) with a resolution of 3.1 × 5.0 × 25.0 mm³ . The ¹³ C spectroscopic images were acquired in 12 s, followed by an 8-min ¹⁸ F-2-fluoro-2-deoxy-d-glucose (¹⁸ F-FDG) PET acquisition with a resolution of 3.5 mm. [1,4-¹³ C₂ ]Malate was observed from the tissue injected with turpentine indicating necrosis. Normal [1-¹³ C]pyruvate metabolism and ¹⁸ F-FDG uptake were observed from the same tissue. The proposed co-polarization scheme provides a means to utilize multiple imaging agents simultaneously, and thus to probe various metabolic pathways in a single examination. Moreover, it demonstrates the feasibility of small animal research on a clinical PET/MR scanner for combined PET and hyperpolarized metabolic MR.

Large dose hyperpolarized water with dissolution-DNP at high magnetic field

We demonstrate a method for the preparation of hyperpolarized water by dissolution Dynamic Nuclear Polarization at high magnetic field. Protons were polarized at 6.7T and 1.1K to >70% with frequency modulated microwave irradiation at 188GHz. 97.2±0.7% of the radical was extracted from the sample in the dissolution in a two-phase system. 16±1mL of 5.0M ¹H in D₂O with a polarization of 13.0±0.9% in the liquid state was obtained, corresponding to an enhancement factor of 4000±300 compared to the thermal equilibrium at 9.4T and 293K. A longitudinal relaxation time constant of 16±1s was measured. The sample was polarized and dissolved in a fluid path compatible with clinical polarizers. The volume of hyperpolarized water produced by this method enables angiography and perfusion measurements in large animals, as well as NMR experiments for studies of e.g. proton exchange and polarization transfer to other nuclei.