Design and performance of a DNP prepolarizer coupled to a rodent MRI scanner

Abstract

For most of the last forty years, the techniques of Dynamic Nuclear Polarization (DNP) have been confined to particle-physics laboratories building polarized targets, but recently it has been shown that samples similar to a solid target can be transformed into room temperature liquid solutions while retaining a high nuclear polarization. This method of ' 'hyperpolarization' ' is of interest in NMR/MRI/MRS. We describe a 3.35 T DNP/9.4 T MRI installation based on a continuous-flow cryostat, using a standard wide-bore low-field NMR magnet as prepolarizer magnet and a widely available radical as polarizing agent. The interfacing to a rodent scanner requires that the infusion of the polarized solution in the animal be remotely controlled, because of limited access inside the magnet bore. Physiological constraints on the infusion rate can be a serious source of polarization loss, and the discussion of efficiency is therefore limited to that of the prepolarizer itself, i.e., the spin temperatures obtained in the solid state. To put our results in context, we summarize data obtained in targets with different types of radicals, and provide a short review of the DNP mechanisms needed in their discussion.

Direct noninvasive estimation of myocardial tricarboxylic acid cycle flux in vivo using hyperpolarized 13C magnetic resonance

“…A total volume of 300 μL of this solution was inserted, in the form of 10 μL frozen beads (prepared in liquid nitrogen), into a 5 T custom-designed DNP polarizer prefilled with liquid helium [38]. The 13 C nuclei were dynamically polarized for 2 h at 1.15 K. Following a previously described automated process [39], the beads were rapidly dissolved in 6 mL of pressurized, heated D 2 O and the resulting solution was transferred within 2 s into a separator/infusion pump located inside an actively shielded 31-cm diameter horizontal bore 9.4 T magnet (Magnex Scientific, Abingdon, UK) [40]. The separator/infusion pump was prefilled with 0.6 mL of phosphate buffered saline and heparin.…”

Feasibility of in vivo15N MRS detection of hyperpolarized 15N labeled choline in rats

“…This solution was polarized at 3.35 T and 1.2 K using a custombuilt polarizer described by Comment et al 35,48 The output power of the 94 GHz microwave source was set to 30 mW. After dissolution into 5 ml of superheated D 2 O pressurized at 10 bars, the solution was automatically transferred within 4 s to a phase separator/infusion pump placed in the bore of the 9.4 T system positioned approximately 4 m away from the DNP polarizer.…”

“…pyruvate, acetate and bicarbonate) have been the most promising candidates. [32][33][34][35] Previous studies have shown the utility of this technique for detecting in vivo tumors in animal models 36,37 and very low contrast agent concentrations. 38 To date, besides optically polarized 3 He and 129 Xe, 39 6 Li is the only hyperpolarized nucleus besides 13 C that has been reported to be detected in vivo.…”

Proton NMR of 15N-Choline Metabolites Enhanced by Dynamic Nuclear Polarization

“…Frozen beads were placed in a home-built prepolarizer 12 and irradiated with 30 mW of microwave power at 94 GHz for 3 h at 1.2 K and 3.35 T. The sample was rapidly dissolved in 5 mL of D 2 O (at ca. 190°C and 12 bar) to a final choline concentration of 50 ( 5 mM.…”