Gamma ray imaging in industrial and medical applications

This thesis details the design and development of solutions for gamma-ray imaging problems in Nuclear Medicine and nuclear decommissioning. The designs presented are: a compact gamma camera for locating the sentinel lymph node, a near-field coded aperture imager for in-vivo imaging of the distribution of a radio-labelled pharmaceuticals in small animals, a coded aperture imager based upon an existing pinhole imager and finally, an imaging system designed to aid in the decommissioning of the Windscale piles, at Sellafield. The design of a coded-aperture imaging system for use in the nuclear industry is presented and its performance is compared with that of an existing pinhole imaging system. The sensitivity of the coded aperture system was demonstrated to be superior to that of pinhole system in high background environments, thus allowing the use of comparatively less shielding. However, the non-uniformity of the PSPMT detector plane was demonstrated to be a limiting factor in the sensitivity of the pinhole imager. In the context of a detector suitable for a scintimamography detector system, a multi-wire data acquisition system was evaluated with a 5" Position Sensitive Photomultiplier (PSPMT) in order to improve upon the poor performance of the resistive divider technique. The readout system improved the useable area of the PSPMT by 36% and the spatial resolution from 1.9 to 1.5 mm when imaging a CsI(Tl) crystal array of 2x2x3mm elements, compared with the resistive divider network. Subsequent to this evaluation the potential of the Multi-pixel Hybrid Photodiode (MHPD) was evaluated as an alternative to the PSPMT in this application. The spatial resolution of the MHPD was measured to be 600 mm with a 1mm thick planar CsI(Tl) scintillator. This data was then extrapolated to generate the parameters of a large area, 72mm diameter, device with a spatial resolution of <1mm.