Dynamic Nuclear Polarisation And Non-Equilibrium Physics

Dyamic Nuclear Polarisation (DNP) is a technique that makes it possible to enhance the signal and hence the sensitivty of magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) spectroscopy. MRI is one of the key modalities in medical diagnostics and NMR spectroscopy is widely used in biomolecular research for structural investigation and in material research for probing molecular properties. The fundamental principle of these techniques is the detection of a weak sample magnetisation that arises from placing the sample (small as in the case of NMR spectroscopy or large as in the case of medical whole body imaging) in a strong magnetic field generated by a magnet. The strong magnetic field interacts on the atomic level with some nuclei (e.g. hydrogen 1H or the stable carbon isoptope 13C) and also any unpaired electron since these nuclei or the electron have also a magnetic moment. In a simple explanation one can envisage the nuclei or the unpaired electron to either align parallel or unparallel with the direction of the external magnetic field. There is a small difference in the order of a few ppm in the number of nuclear that align parallel and antiparallel with the magnetic field and this difference between these two groups gives rise to the signal used in MRI or NMR. If it would be possible to align all nuceli in the same orientation the signal would dramatically increase. However, the thermal energy in the sample usually prevents the perfect alignment but it has been shown that the nuclei can be aligned with the help of unpaired electrons. The process of aligning nuclei with the help of electrons is called DNP. The underlying physics is complex because all nuclei interact with each other as well as with the electron and the alignment process follows the rules of quantum mechanics. Interestingly, we have recently discovered that some of the dynamical aspects in a large system containing many interacting nuclei and an electron are identical to properties of other systems containing a large number of interacting particles such as for instance systems changing their state in a glass transition. In our project we will investigate the links between DNP and other non-equilibrium systems to find out whether such systems share more common properties which perhaps can be described by generalising rules. Furthermore, we propose to develop models that predict the dynamics of systems of many nuclei during DNP experiments. The goal here is to gain enough insight so that DNP experiments can be made more efficient by providing even a higher signal enhancement in a shorter time.

The knowledge and insight that this theory-led project will deliver will produce impact on several levels. Any optimisation strategy that delivers an increased nuclear spin polarisation in comparison to the current state of the art will immediately benefit DNP applications that are currently developed at the University of Nottingham (UoN) and a number of DNP research groups worldwide. Funded by the Medical Research Council, we are constructing at the UoN hospital a sterile DNP polariser for clinical applications. These include novel methods for studying muscle pathology, brain metabolism and cancer diagnostics. All these applications crucially depend in the first instance on the efficient generation of high nuclear spin polarisation by DNP. In addition, we have recently installed the first commercial 395GHZ/600MHz DNP MAS NMR spectrometer in the UK which will be operated as a facility with open access for the UK science community supported by EPSRC equipment grant (EP/L022524). Results obtained in WP2 will feed into research carried out with our new spectrometer and will enhance the activities funded by the EPSRC equipment grant (EP/L022524). From this it is clearly evident that the proposed project will have an direct impact on the DNP related research activities at our University.

In additioon to the expected effect on ongoing DNP projects, the research described in this proposal will have a much broader impact as it tackles fundamental questions in the realm of non-equilibrium quantum dynamics. In our research programme we propose to use DNP for investigating general aspects of the many-body spin systems far from equilibrium. The questions addressed by our proposal fall into the remit of the EPSRC Physics grand challenge \emph{Emergence and Physics Far From Equilibrium} and thus establish a direct link to the topical domain of non-equilibrium phenomena in general. They also link specifically to the EPSRC funded research projects ({\em Non-equilibrium Dynamics of Quantum Open Systems}, EP/I017828/1) and {\em Rydberg Soft Matter} (EP/M014266/1). \\

Both NMR spectroscopy and MRI are methods widely used in many research disciplines. MRI is one of the most important imaging modalities in medical diagnostics. Since our research ultimately aims to improve these techniques and to develop more sophisticated applications, it is clear that the impact on society and economy can be substantial. We maintain close links to a number of commercial enterprises that are involved in the design and manufacturing of MR instruments (Bruker, the leading manufacturer of NMR spectrometers is funding currently a PhD studenthip in WK's lab for a project related to DNP). Any invention or novel strategies for DNP are of immediate commercial interest and we will use our established links to the industrial sector to ensure that the technology will be made available to a wider user community.