This thesis investigates the use of SABRE as a hyperpolarisation method within the Earth's magnetic Field (EFNMR) and develops an EFNMR apparatus to optimise sensitivity, resolution and performance.
A fundamental problem in NMR and MRI is the inherent low sensitivity of the techniques due to the nature of the normal spin distribution at room temperature and in currently available magnets.This Boltzmann distribution means that few nuclear magnetic moments contribute to the detected signal. Hyperpolarisation is a method used to counter this by enhancing the NMR signal. SABRE, a new hyperpolarisation method for creating a very skewed distribution in the population of spins in a substrate does so without changing its chemical structure and offers the potential to make measurements at lower concentrations previously thought possible. Moreover, this method achieves its novel spin distribution in low field, and therefore provides an opportunity to also detect signals in low field thus, obviating the need for a high field magnet for specific applications.
This project is concerned with the investigation and use of a low field magnetic resonance device to optimize the detection and imaging of nuclear spin from molecules that have been subject to SABRE hyperpolarisation. It includes the description of the background for the investigations, the creation of an optimal devices for imaging and detection as well as for a study of the optimization of hyperpolarisation for molecules that are of biological significance.
The thesis focuses on optimising the SABRE technique in the earth's magnetic field and the primary results show how the signal enhancement is affected by several factors such as the amplitude of the pre-polarisation field, its duration, and the flip angle of the excitation pulse. The relationship between signal enhancement and a range of
dependencies such as the parahydrogen pressure in the test tube, the effect of multiple shakes of the sample and the possibility of achieving 2D imaging by using SABRE in the earth's field have been investigated.
The improvement of the hardware and the software of a purpose-built system employed to produce a versatile earth's field spectrometer is described. Therefore, instead of being limited to a hard excitation pulse it is possible to employ this new system to generate trains of sine excitation pulses. In particular it is possible to create long sequences of, differing, arbitrary shapes (composite pulses).
The observations shown in the final chapter highlight the efforts made to progress the SABRE technique into advanced measurements in the earth's magnetic field such as polarising the sample in one place and performing the excitation/detection in another location. In addition, dedicated measurements were done to observe the long lived states of Aminothiazole and Fluoropyridine in the earth's magnetic field. However, these initial studies did not reveal evidence of a long-lived states, but a proposed plan to complete the long-lived SABRE measurement is given as future work.
