[en] This thesis is primarily concerned with the development of novel detector techniques for Positron Emission Tomography (PET). In recent years, PET has evolved to the extent that the technique is routinely used to provide valuable quantitative information related to a variety of health care problems. A review of the concepts and techniques associated with PET imaging systems is presented, including the performance characteristics of current systems. This review concludes by highlighting a number of key design features that should be incorporated in new PET systems. Following this review, work is presented on the development of two novel PET detector systems that seek to meet some of these objectives. Both designs, though significantly different, have the potential to provide high resolution imaging (<2mm) with low dead- time (<100ns), a depth-of-interaction capability (5-10mm), a high packing-fraction and a minimal perimeter dead-space. Also, as a consequence of the novel fibre readout methods employed, the detector modules should prove to be very cost-effective. In addition to this, both detectors are capable of operation within the coil of an MRI scanner in order to co- register the PET data with a high-resolution anatomical image. The final chapter concerns an extensive study into the characterisation and analysis of the energy-resolution performance of arrays of small scintillation crystals. Such arrays are commonly used for both PET detectors and some gamma camera designs. This study was intended to provide insights into improving the energy-resolution through scintillator optimisation, and also to form the basis of an accurate detector-response function for such arrays. This could be used to apply a spectral-deconvolution technique that has recently achieved great success when applied to conventional gamma-ray spectrometers, improving the energy-resolution from 12% to 3% at 662keV. This spectral-deconvolution, if successfully applied to gamma cameras, might result in an energy-resolution performance comparable to that of current room temperature semi-conductor detectors. (author)

[en] In this paper we present some recent results we have obtained in the development of detectors for small animal PET and for PEM, based on the use of Position Sensitive PMTS or Hybrid Photo Diodes (HPDs) coupled to crystal matrices. New ideas and future developments are discussed

[en] The Silicon PhotoMultiplier (SiPM) APD represents an interesting advance in photodetection and could soon be a rival to traditional PMTs in many applications. The SiPM is effectively a densely packed 2D array of Geiger-mode APD microcells, each having individual resistive quenching and multiplexed outputs. In this way the SiPM acts as a linear, high-gain photodetector for moderate photon flux (N_photon< N_cells). The Metal-Resistor-Silicon (MRS) structure SiPM, produced by CPTA Russia, has been characterised and tested for scintillator light detection in medical applications such as PET. We present a summary of measurements of the device's primary operating characteristics and results of the application to scintillator readout

[en] Commercially constructed crystal matrices are characterised for use with PSPMT detectors for PET system developments and other nuclear medicine applications. The matrices of different scintillation materials were specified with pixel dimensions of 1.5x1.5 mm² in cross-section and a length corresponding to one gamma ray interaction length at 511 keV. The materials used in this study were BGO, LSO, LYSO, YSO and CsI(Na). Each matrix was constructed using a white TiO loaded epoxy that forms a 0.2 mm septa between each pixel. The white epoxy is not the optimum choice in terms of the reflective properties, but represents a good compromise between cost and the need for optical isolation between pixels. We also tested a YAP matrix that consisted of pixels of the same size specification but was manufactured by a different company, who instead of white epoxy, used a thin aluminium reflective layer for optical isolation that resulted in a septal thickness of just 0.01 mm, resulting in a much higher packing fraction. The characteristics of the scintillation materials, such as the light output and energy resolution, were first studied in the form of individual crystal elements by using a single pixel HPD. A comparison of individual pixels with and without the epoxy or dielectric coatings was also performed. Then the matrices themselves were coupled to a PSPMT in order to study the imaging performance. In particular, the system pixel resolution and the peak to valley ratio were measured at 511 and 122 keV

[en] Positron Emission Tomography (PET) for small animal studies requires high-resolution gamma cameras with high sensitivity. Traditionally, inorganic scintillators are used and, in recent times, coupled to position sensitive PMTs to achieve a higher resolution. Such PSPMTs are costly, operated at high voltage and have a relatively low packing fraction. However, their advantage, compared to current solid state photodetectors, is their high signal-to-noise ratio. The Silicon Photomultiplier (SiPM) is a silicon diode detector that shows great promise as a photodetector for scintillators and hence application in nuclear medicine imaging applications. The microcell MRS (Metal-Resistor-Semiconductor) structure of the SiPM leads to a self-quenching, Geiger-mode avalanche photodiode (GAPD), that produces a large gain (5x10⁵) at low bias voltage (50V) and proportional output for moderate photon flux. Such a compact silicon detector, with a performance similar to a PMT, is obviously well disposed to being developed into a close-packed array in order to have a position-sensitive detection surface. We propose a miniature, high-resolution camera for a small-animal PET imaging system that is based on such an array of SiPM. The design is based upon the classic Anger camera principle; each detector module consists of a continuous slab of scintillator, viewed by a matrix of SiPM. A detector head of 4x4cm² in area is proposed, constructed from three such modules of the continuous camera described above. The stacked layers would give the system intrinsic depth of interaction (DOI) information. A summary of measured SiPM performance and results of a simulation of the proposed camera, using the Monte Carlo package GEANT4, are presented. It is shown that using three layers of 5mm thick LSO, gives an efficiency of 68% with maximum count rates in the front layers. Intrinsic spatial resolution of <0.4mm FWHM was found although this is degraded at the edges. Although the inclusion of DOI information increases the overall spatial resolution, the parallax error was still found to be the limiting factor in a small animal system