Design and performance of a small bath cryostat with NMR capability for transport of hyperpolarized samples

Abstract

As of today, dissolution Dynamic Nuclear Polarization (dDNP) is the only clinically available hyperpolarization technique for 13C-MRI. Despite the clear path towards personalized medicine that dDNP is paving as an alternative and/or complement to Positron Emission Tomography (PET), the technique struggles to enter everyday clinical practice. Because of the minute-long hyperpolarization lifetime after dissolution, one of the reasons lies in the need and consequent complexities of having the machine that generates the hyperpolarization (i.e. the dDNP polarizer) on site. Since some years, research groups are working to make hyperpolarization transportable. Two different methods have been developed that allow “freezing” of the nuclear spin state prior to samples extraction from the polarizer. Nevertheless, so far, all attempts of transport have been limited to a very small scale and to the level of proof-of-principle experiments. The main reason for that is the lack of adequate hardware, strategy, and control on most of the crucial parameters. To bridge the technical gap with PET and provide MRI facilities with hours long relaxing hyperpolarized compounds at controlled conditions, a new generation of low cost/small footprint liquid He cryostats equipped with a magnetically enforced cryogenic probe is needed. In this paper, we detail the theoretical and practical construction of a hyperpolarized samples transportation device small enough to fit in a car and able to hold a sample at 4.2 K for almost 8 h despite the presence of a cryogenically-demanding purpose-built probe that provides enough magnetic field upon insertion of the sample and NMR quality homogeneity at storage position. Should transportable hyperpolarization via DNP become a reality, we herein provide important details to make it possible.

Long-Lived, Transportable Reservoir of Nuclear Polarization Used to Strongly Enhance Solution-State NMR Signals

“…Alternatively, photogenerated radicals that disappear upon heating of the sample have been used as PA to hyperpolarize 13 C-labeled metabolic contrast agents. , Thus, shortening of the lifetime of the nuclear spin polarization due to the PA could be eliminated and carbon relaxation times of 4 h at 1 T and 4.2 K were obtained for a 13 C-labeled glucose sample . Very recently, a helium bath cryostat enabling storage for up to 8 h of such samples has been developed and used for the transport of a polarized sample over a long distance…”

Parallel detection of chemical reactions in a microfluidic platform using hyperpolarized nuclear magnetic resonance

“…Advances in dDNP-MR have improved polarization efficiency, 12,13 chemical formulations to avoid persistent radicals in the sample [14][15][16][17] and lifetime of spin hyperpolarization in the solid state for sample transportation. 3,18,19 However, the application potential of dDNP-MR is still limited by the time-consuming polarization build-up process and fast relaxation of the nuclear magnetization post dissolution. For instance, polarization time of [1- 13 C]pyruvate is usually on the order of tens of minutes, while T 1 relaxation is on the order of tens of seconds at room temperature.…”

129Xe Dynamic Nuclear Polarization Demystified: The Influence of the Glassing Matrix on the Radical Properties

“…Unpaired electron spins in the form of organic free radicals represent the source of the polarization. Generally, they are added to the sample by chemical doping. , More recently, other strategies involving polarizing matrices , and nonpersistent photoinduced radicals − were developed with the intent of facilitating radical filtration and enabling transport of hyperpolarization. − …”