Quadrupolar relaxation-based methods in Fast Field-Cycling MRI Nicholas R. Payne Aberdeen Biomedical Imaging Centre, University of Aberdeen, AB25 2ZD, Scotland, UK Fast Field-Cycling MRI (FFC-MRI) can access contrast based on the dependence of a sample's relaxation rate to the applied magnetic field strength. This technique can provide signal based on interactions with local quadrupolar nuclei through cross-relaxation, however, there are other so-called Nuclear Quadrupole Double Resonance (NQDR) techniques described in the literature. This work has been centred on efforts to apply these techniques to FFC-MRI and otherwise explore how interactions between protons and quadrupolar nuclei can be further exploited. Through this work two irradiation systems were designed and built for manual tuning, in the first instance, and automatic tuning. The latter was able to quickly retune to coil, however, it was limited in RF power handling capability. A second strand of work was concerned with the reduction in receiver deadtime required to detect signal from solid-state samples such as those previously used in NQDR experiments in the literature. However, circuitry designed to dampen coil ringing by temporarily reducing the resonator's Q-factor following a pulse, along with a novel method utilising field-cycling were not able to reduce the deadtime enough to detect signal from relevant samples. This, coupled with a lack of evidence of NQDR effects in gel-like samples, proved the ultimate stumbling block for NQDR in FFC-MRI. Success was seen in a third strand of work in which simulations were used to design custom experiments which could be used to provide large increases to the signal-to-noise ratio in some experiments. The simulated environment also allowed for fast testing and development of new post-process algorithms which could more accurately calculate relaxation rates. The work concluded that NQDR is unlikely to be useful in FFC-MRI due to the constraints on both the sample and the technique. However the information from quadrupolar nuclei can be improved with better post-processing and tailored pulse sequence parameters.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:767352 |
| Date | January 2019 |
| Creators | Payne, Nicholas Roy |
| Contributors | Lurie, David ; Levitt, Malcolm H. ; Broche, Lionel M. |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=240235 |
Page generated in 0.0021 seconds