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

Abstract

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).

Parahydrogen-induced polarization and spin order transfer in ethyl pyruvate at high magnetic fields

“…We observed 40 s at neutral and acidic conditions (pH below 7) while 60 s at basic pH (pH above 10). Using the same 1 T spectrometer and 1- 13 C-pyruvate polarized with dDNP we observed a 13 C-T 1 of 90 s 30 , meaning that there can be some impurities in our reagents which increases the relaxation rate of 1- 13 C-pyruvate.…”

“…The starting compound is an unsaturated pyruvate ester such as vinyl, propargyl, allyl, or another unsaturated ester, which is commonly labeled with 13 C in 1-position 29 . After hydrogenation with pH 2 and SOT, the reduced ester is cleaved yielding pyruvate that is hyperpolarized at the 1-13 C nucleus with a relaxation time around 1 min 21,30 . Hence, all manipulations have to be performed rapidly to avoid loss of polarization.…”

“…The rate of production of PHIP-SAH polarized samples is significantly higher and semicontinuous hyperpolarization is possible already, i.e., we can repeat experiments every few minutes without automation 14 . For dDNP, typically, 60 mM pyruvate in a 4 mL aqueous solution were polarized to 50% 13 C polarization right after dissolution 30 . This corresponds to 3 M% molar polarization and 12 mmol% molecular polarization.…”

Highly versatile dissolution DNP: implementation of a multi- sample/multi-nucleus cryogenic probe with parallel NMR detection

“…In the present work, we detail the design and performance of a highly versatile and customizable dDNP cryogenic probe, herein adapted to a 5 T "wet" preclinical polarizer 41 , that, employing a Custom Fluid Path (CFP) 18,42 , can not only co-polarize up to three samples, but it is also capable of monitoring the solid-state dynamic of each of them separately, thanks to dedicated pseudo-Alderman-Grant (AG) coils and multi-nucleus parallel Nuclear Magnetic Resonance (NMR) acquisition on three distinct channels. We tested the system for the generation of three HP solutions of the same substrate (i.e.…”

“…Differently, we employ CFPs that allow more exibility in terms of reusability and nature (i.e. liquid or solid) of the compound of interest upon loading 7,18,41,42 . The 1470 mm long cryogenic probe is built around a 316L stainless steel 3-arms manifold (H) composed by a 58.3/68.0 mm ID/OD tube with 3 ISO-KF16 half-nipples welded on it at a 30° angle (G).…”