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The University of Southampton

Hyperpolarised NMR

The enormous signal enhancement achieved through hyperpolarisation techniques is currently revolutionising the range of NMR, extending the method into new areas such as in vivo characterisation of cancer metabolism in humans and the NMR of thin surface layers.

Quantum-rotor-induced polarization in g-picoline

Hyperpolarisation techniques enormously increase the signal strength of NMR experiments, with enhancements exceeding 4 orders of magnitude demonstrated experimentally. The available hyperpolarisation techniques include spin-exchange optical pumping (restricted to noble gases such as 129Xe), parahydrogen-induced polarisation (PHIP), its variant signal amplification by reversible exchange (SABRE) and dissolution-dynamic nuclear polarisation (dDNP). In our laboratory we are working on dDNP and PHIP.

The PHIP method consists in preparing para-enhanced hydrogen gas by deposition of hydrogen on a cold (typically <77K) paramagnetic surface (charcoal, Fe2O3 or similar) and then reacting this with an unsaturated bond present in the molecule of interest. The addition reaction transfers the hyperpolarised (singlet) order from para-H2 to the molecule of interest which can now produce enhanced NMR signals.

The dDNP method transfers the very high thermal polarisation of electrons at low temperatures (~100% at 1.5K) to nuclear spins by applying microwaves. A molecular substrate is mixed with a substance containing unpaired electrons and cooled to about 1.5K. The sample is irradiated with microwaves in the presence of a magnetic field to establish the nuclear polarisation and then rapidly dissolved by a stream of hot solvent. This produces a solution with a high degree of hyperpolarised Zeeman order as well as some hyperpolarised singlet order. Most substances may be hyperpolarised this way, unless they do not tolerate the extreme conditions.

The availability of general-purpose hyperpolarisation methods such as dDNP have revolutionary impact. Some experiments that were considered to be impossible, such as the metabolic imaging of human cancer by MRI, have now been demonstrated in a clinical context. Nevertheless all such applications still remain on the borderline of feasibility. For example the spatial resolution of hyperpolarised MRI imaging of cancer metabolism is strongly compromised by the loss of signal during transport and purification of the hyperpolarised material. Improvements to hyperpolarisation protocols and the ability to transport hyperpolarised material would improve the emerging techniques and open up new areas.

Our efforts in this area are focused on:


  1. building a 188 GHz nuclear spin polariser for dissolution-DNP
  2. developing new methodology for the dissolution of hyperpolarised samples
  3. investigating the phenomenon of quantum-rotor-induced polarisation
  4. developing a device that uses parahydrogen-enhanced polarization (PHIP) to generate a continuous flow of hyperpolarized material for practical applications
  5. developing pulse sequence for the efficient conversion of hyperpolarised singlet order (generated via PHIP) into hyperpolarised magnetisation
  6. combining hyperpolarisation techniques with long-lived spin states to obtain long-lived reservoirs of hyperpolarisation
  7. combining dissolution-DNP with supercritical fluids for storage and transport of hyperpolarised spin order
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