Spin dynamics of signal amplification by reversible exchange

All matter is made up of atoms, each containing a tiny nucleus at its centre. When placed in a magnetic field, these nuclei behave like microscopic magnets due to an intrinsic property called spin. The interaction between the nuclear spins and the magnetic field can be studied by observing how the spins respond to electromagnetic radiation. This technique is known as nuclear magnetic resonance (NMR).

NMR provides rich information about the local environment of the spins, making it an essential tool in chemistry, materials science, and medical imaging. However, NMR signals are generally very weak due to low spin polarisation, making it difficult to study dilute samples. This limitation can be addressed using hyperpolarisation methods, which significantly enhance the NMR signal. One such method, called signal amplification by reversible exchange (SABRE), uses parahydrogen gas as a source of polarisation. In SABRE, the polarisation is transferred to a target molecule by temporarily binding both parahydrogen and the target molecule to a metal complex.

In this thesis, experimental, computational, and theoretical methods are used to provide a better understanding of the underlying physics of SABRE and to find ways to make the method more efficient. The main focus is on the hyperpolarisation of fluorine-19 nuclei, which are attractive for biomedical imaging applications due to the lack of background signal from the body. The results explain the key physical mechanisms responsible for transferring polarisation from parahydrogen to fluorine-19 and demonstrate how carefully chosen magnetic fields can be used to improve fluorine-19 polarisation. In addition, a new analytical model for SABRE hyperpolarisation is developed, providing a foundation for understanding and optimising SABRE experiments.