Field-cycled proton-electron double resonance imaging of dissolved oxygen
Field-Cycled Proton-Electron Double Resonance Imaging (FC-PEDRI) is a new imaging technique that has potential for detecting and monitoring concentrations of dissolved oxygen in aqueous solutions. This technique is based upon the magnetic interactions that can occur between nitroxide free radicals and water molecules. This thesis describes why the FC-PEDRI signal is sensitive to dissolved oxygen and explores different methods of making quantitative measurements of oxygen concentration using FC-PEDRI. It starts by developing a comprehensive theoretical model which describes all the relevant magnetic interactions which can occur between nitroxide molecules, molecules of dissolved oxygen and solvent water protons. It was found that the complicated chemical structure of nitroxide molecules can greatly affect the oxygen-sensitivity of the FC-PEDRI signal. Methods of correcting for some of these effects are discussed. The instrumentation necessary to perform FC-PEDRI oximetry is also described, as is the implementation of oxygen-sensitive FC-PEDRI pulse sequences. The success of these sequences was found to be strongly dependent on the performance of the field-cycling apparatus. Two different FC-PEDRI instruments are described in this thesis. The construction and commissioning of one of these instruments is fully discussed. This instrument was large enough to allow in-vivo FC-PEDRI experiments to be undertaken and was based upon the use of novel field-cycling control electronics. The improved operation of this machine, in comparison to that of the older instrument, allowed the oxygen-sensitive pulse sequences developed in this thesis to be performed much more satisfactorily.