Collimator design in SPECT, an optimisation tool

Traditional gamma camera collimators have been based on a standard parallel design, usually with parallel holes. The collimator determines the resolution of the camera, but is also the determining factor of the number of counts detected. The uncertainty about the origin of the detected photons is modelled by a Point Spread Function (PSF), which, in literature, is normally assumed to be a Gaussian function, whose full width at half maximum (FWHM), is determined by the collimator's aperture. In this paper, these traditional assumptions will be abandoned. From related work it appears possible to improve resolution recovery based reconstruction by considering different shapes of PSF. A novel collimator geometry has been then proposed, that does not imply necessarily parallel holes, but could involve a polygonal shape of the septa. To model the geometrical and septal penetration component of the point source response function a ray-tracing algorithm has been coded. In addition we developed an optimisation method that, given a target PSF, determines the optimum collimator geometry using a genetic algorithm.