In the work described in this thesis, new techniques to reduce the electron paramagnetic resonance (EPR) irradiation power required in field cycled proton electron double resonance (FC-PEDRI) and to improve the temporal resolution of FC-PEDRI have been investigated. These are the aims of this work. Details of free radicals and basic principles of EPR and EPR imaging are given and the fundamentals of NMR are also described. The principles of NMR imaging (MRI) are summarised and the essential hardware of MRI for the experiments are also described. Details of PEDRI and FC-PEDRI are also described in this thesis. It is widely realised in MRI that a surface coil, or local RF coil, generates very strong magnetic fields in the coil proximity and that the field decreases rapidly with the distance away from the coil. This should be a useful advantage to limit the EPR irradiation within the desired area of the sample. Hence, the use of a surface coil as an EPR irradiation resonator has been investigated. Not only is the EPR irradiation restricted to the area of interest close to the surface coil but a stronger RF field and high SNR are also generated in this region too. The double resonance coil assembly developed here consisted of a split-solenoid coil (for NMR) and a loop-gap resonator surface coil (for EPR). The results confirmed that the enhancement of NMR signal was higher compared to the whole-body birdcage EPR coil used previously and that the enhancement area was restricted within the proximity of the surface coil. Using the technique of rapid imaging in NMR with FC-PEDRI, fast imaging of free radicals has been investigated. A number of fast pulse sequences are presented in this thesis. A snapshot centric-reordered phase-encoding pulse sequence using the technique of population preparation has been studied and employed. With an essential ideal of EPR irradiation applied only once followed by a snapshot NMR imaging pulse sequence, the EPR power is greatly reduced and the temporal resolution is greatly improved, too. However, the experimental results showed that the image quality needed much improvement and this technique is still limited to be used with samples where the longitudinal relaxation time (Ti) is longer than 250 ms. Next, the rapid imaging of free radicals in very short Ti samples equivalent to biological tissue (typically Ti of -150 ms) was investigated. The basis of image artefacts was studied. From the experimental results, it was found that the snapshot NMR pulse sequence must be commenced very soon after the end of field cycling to avoid the signal enhancement decay. To address the problem of image artefacts, the NMR FID data have been analysed. As a result, phase shift correction and amplitude adjustment schemes have been adopted and applied to the FID data. Details of the data correction schemes are given. Experiments employing rapid imaging of free radicals in vivo using FC-PEDRI are presented. The results show that the rapid imaging in vivo using this technique are possible. However, the resulting images are still noisy. More study is required for further refinement of this technique. Experiments using EPR surface coils with rapid FC-PEDRI were also investigated. The preliminary results obtained from biological-equivalent samples show the possibility of the use of this method in in vivo experiments.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:635955 |
| Date | January 1999 |
| Creators | Puwanich, Patana |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU602006 |
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