Measuring absolute spin polarization in dissolution-DNP by Spin PolarimetrY Magnetic Resonance (SPY-MR)

Abstract

Dynamic nuclear polarization at 1.2 K and 6.7 T allows one to achieve spin temperatures on the order of a few millikelvin, so that the high-temperature approximation (ΔE<kT) is violated for the nuclear Zeeman interaction ΔE=γB0h/(2π) of most isotopes. Provided that, after rapid dissolution and transfer to an NMR or MRI system, the hyperpolarized molecules contain at least two nuclear spins I and S with a scalar coupling JIS, the polarization of spin I (short for 'investigated') can be determined from the asymmetry AS of the multiplet of spin S (short for 'spy'), provided perturbations due to second-order (strong coupling) effects are properly taken into account. If spin S is suitably discreet and does not affect the relaxation of spin I, this provides an elegant way of measuring spin polarizations 'on the fly' in a broad range of molecules, thus obviating the need for laborious measurements of signal intensities at thermal equilibrium. The method, dubbed Spin PolarimetrY Magnetic Resonance (SPY-MR), is illustrated for various pairs of (13)C spins (I, S) in acetate and pyruvate.

Imaging of Extracellular pH Using Hyperpolarized Molecules

“…The polarization enhancement ( ϵ ) is the ratio of the hyperpolarized signal ( S hyper ) to the thermal signal ( S thermal ) measured under the same experimental conditions. The polarization level ( P hyper ) can be determined by multiplying the thermal polarization level P thermal with ϵ (equation : …”

Transport of hyperpolarized samples in dissolution-DNP experiments

“…Here we provide an explanation for the dependence of the appearance of the detected multiplets on B trans . We argue that these effects can be traced back to proton polarizations in coupled two-spin systems that can reach almost P( 1 H) = 100%, 18 resulting in the formation of a 'population imbalance' 19 between the triplet and singlet states, known as Triplet-Singlet Imbalance (TSI) after rapid transfer to solution state conditions. Generally, the amplitudes of the components of the multiplets reflect the polarization.…”

“…In principle, this allows one to determine the absolute spin polarization by spin polarimetry magnetic resonance. 18 It is well documented [20][21][22] that a TSI can constitute a long-lived state (LLS), i.e. it can have a lifetime T LLS that is longer than the relaxation time T 1 of the individual participating spins.…”

Voxel-by-voxel correlations of perfusion, substrate, and metabolite signals in dynamic hyperpolarized13C imaging

“…It is important to note that lactate signal normalization using the signal from a HP perfusion agent generally does not account for polarization, as the substrate and perfusion agent may have different initial polarizations. One approach to polarization normalization may involve measuring the absolute spin polarization using a spin‐coupled nucleus . The sample preparation protocol for this study included adding 10% [1,2‐ 13 C 2 ]pyruvic acid to the [1‐ 13 C]pyruvic acid, which would facilitate the measurement of the pyruvate C 2 asymmetry in the spectroscopy interleaf to estimate the pyruvate C 1 polarization without appreciable signal contamination in the pyruvate imaging interleaf .…”