MODELING THE FACTORS AFFECTING IMAGE QUALITY FOR THE RAL BIRMINGHAM POSITRON CAMERA

The RAL-Birmingham positron camera is based on position sensitive multiwire technology developed originally for particle physics. It provides quantitative images of positron emitting tracers in a wide variety of process engineering research applications. A simulation of the camera has been developed to give insights into how the physical processes underlying positron-based imaging affect the overall performance. It is shown, by comparison with real data, that the simulation reproduces the useful data logging rate and spatial resolution to within 5% of the real values over the whole field of view. It reproduces the detector efficiency as a function of energy to better than 10% in the range 50 keV to 511 keV and better than 15% in the range 511 keV to 1.3 MeV. A series of point source measurements has been simulated to study the effect on spatial resolution of photon scattering in the object and in the detectors themselves. This shows that detector scatter contributes 0.9 mm to the FWHM and 3.2 mm to the FWTM of the point spread function (PSF) of a central F-18 source. Scatter in the object, or additional gamma-rays accompanying positron decay, produces a broad background on the PSF that contains little spatial information.