To serve well as luminescent labels in biological applications, complexes of the lanthanide ions need to fulfil many criteria, including the requirement of high quantum yields, stability towards dissociation in biological media and preferably, excitation at wavelengths over 350 nm. Herein, a number of aspects regarding the sensitization of europium(III) and terbium(III) ions are discussed with respect to the design and development of novel complexes. The effect of the addition of anions such as fluoride and phosphate to the Eu(III) and Tb(III) complexes of a known tris(bipyridyl) cryptate, are studied with a view to gaining a better understanding of non-radiative deactivation pathways of the lanthanide excited state. Enhancements of Eu3+ emission within the cryptate are noted whilst with the Tb3+ analogue, emission is significantly reduced upon displacement of OH by these ions. A new ligand based on a polyaminocarboxylate structure with a single bipyridyl chromophore is then reported, which displays nine-coordination around the enclosed lanthanide ion. The luminescence properties of the europium complex are very good but the terbium complex shows more complex behaviour, suggestive of a back energy transfer mechanism from the terbium excited state to the ligand triplet level. The development of ligands with mixed N,O pyrido-phenol chromophoric groups, which are expected to be better sensitizers of terbium(III) luminescence, is also outlined. Finally, in the quest to sensitize europium using longer wavelengths, acridone is incorporated into an azamacrocyclic structure and luminescence is observed from the complexed Eu3+. The quantum yield of luminescence is found to increase with decreasing distance between the sensitizer and the ion, and in the presence of coordinating donor atoms.

Positron Emission Tomography (PET) is an imaging technique that uses biologically relevant molecules labelled with positron emitting radioisotopes to measure regional tissue function in living organisms. To maximise the detection efficiency, data are acquired in 3D, that is, all possible detector combinations in a scanner without inter-ring shielding (septa). The gain in sensitivity afforded by 3D PET is offset by the increase in random coincidences, scattered coincidences and deadtime. These problems must be overcome for the gain in sensitivity to be fully realised. The aim of this research project was to investigate strategies to increase the signal to noise ratio of the 3D PET data. Additional side shielding, both in neuro and body scanning, has been implemented and assessed. Large gains were achieved using the neuro shields in experimental and clinical studies. The potential of the body shields was tested in experimental and in-vivo studies which showed that they were scan dependent. For example, no gain was found for a cardiac blood flow (H2 IS0) study. A model-based scatter correction was assessed by companng compartment ratios within the 'Utah' phantom with radioactivity outside the field of view, with and without neuroshielding. Recovered ratios were within 6% of their actual values. The integration time was reduced in an effort to decrease the system deadtime. A peak increase of 150/0 in noise equivalent count rate was measured for a uniform cylinder inside the field of view. A random coincidence variance reduction technique was implemented and assessed to reduce the noise contained in the delayed window random coincidence estimate. The algorithm was evaluated using phantoms and tested on clinical data. A mean 16% reduction in coefficient of variation was measured for a C15O torso study.

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