High-power closed-cycle 4He cryostat with top-loading sample exchange

Piegsa, F. M.; Brandt, B. van den; Kirch, K.

doi:10.1016/j.cryogenics.2017.08.010

Cited by 3 publications

(1 citation statement)

References 25 publications

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“…The recent developments in cryocooler technology have enabled the implementation of new designs of dissolution DNP polarizers based on closed‐cycle helium refrigerators, which do not require an external supply of liquid helium. The most straightforward scheme incorporates a closed loop aimed at recondensing the helium gas collected from the output of the mechanical vacuum pump to feed it back into the sample space through a circuit cooled by a cryocooler and controlled by a needle valve . Instead of pumping directly on the sample space, it is possible to integrate a separate pumped helium bath referred to as a “1‐K pot”, which conductively cools the sample space.…”

Section: Introductionmentioning

confidence: 99%

A multisample 7 T dynamic nuclear polarization polarizer for preclinical hyperpolarized MR

et al. 2020

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Dynamic nuclear polarization (DNP) provides the opportunity to boost liquid state magnetic resonance (MR) signals from selected nuclear spins by several orders of magnitude. A cryostat running at a temperature of~1 K and a superconducting magnet set to between 3 and 10 T are required to efficiently hyperpolarize nuclear spins.Several DNP polarizers have been implemented for the purpose of hyperpolarized MR and recent systems have been designed to avoid the need for user input of liquid cryogens. We herein present a zero boil-off DNP polarizer that operates at 1.35 ± 0.01 K and 7 T, and which can polarize two samples in parallel. The samples are cooled by a static helium bath thermally connected to a 1 K closed-cycle 4 He refrigerator. Using a modified version of the commercial fluid path developed for the SPINlab polarizer, we demonstrate that, within a 12-minute interval, the system can produce two separate hyperpolarized 13 C solutions. The 13 C liquid-state polarization of [1-13 C]pyruvate measured 26 seconds after dissolution was 36%, which can be extrapolated to a 55% solid state polarization. The system is well adapted for in vitro and in vivo preclinical hyperpolarized MR experiments and it can be modified to polarize up to four samples in parallel. K E Y W O R D Scarbon-13, cryogen-free, cryostat, dynamic nuclear polarization, hyperpolarization, hyperpolarizer, MRI, MRS | INTRODUCTIONDynamic nuclear polarization (DNP) is currently the most efficient and versatile method for hyperpolarizing nuclear spins of molecules in order to obtain enhanced magnetic resonance (MR) signals in solution. 1,2 Numerous preclinical applications have demonstrated the enormous potential of hyperpolarized 13 C MR for in vivo metabolic imaging, 3,4 and several research hospitals are currently performing studies on patients. 5,6 To achieve a high nuclear spin polarization by DNP, the samples containing the molecules of interest have to be doped with either a stable or a nonpersistent radical and cooled to a temperature of 1-1.5 K in a magnetic field of 3-10 T. 7,8 Moreover, they need to be irradiated with microwaves at a frequency near the electron spin resonance (ESR) of the unpaired electron spin of the selected radical. Finally, to transform the cold samples into solutions containing molecules with hyperpolarized nuclear spins, a dissolution or a thermalization and melting process is required. 2,9 The original dissolution DNP polarizer was implemented using a cryostat with a pumped liquid helium bath, in which the sample was directly inserted. 10 In this system, the temperature of the sample is lowered by dynamically reducing the vapor pressure above the liquid

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Section: Introductionmentioning

confidence: 99%