Pinhole collimator design for nuclear survey system

A conventional knife-edge collimator, which is widely used in gamma camera for medical diagnosis, is not suitable for nuclear imaging system because many scattering radiations near the pinhole aperture happen and blur image. A new pinhole collimator, which shapes a channeled aperture for reducing image degradation induced by the scattering radiations, is introduced and its characteristics are analyzed by Monte Carlo simulation. Resolutions defined as the full-width at half-maximum (FWHM) of point spread function and efficiencies are calculated about several pinhole diameters from 4 to 8 mm and channel heights from 2 to 10 mm. For this calculation, we assumed that 137Cs radiation sources with 662 keV mono-energies enter into our designed collimator at the 1 m distance from the detector plane. The efficiencies and resolutions of the channeled collimator are compared with those of the conventional collimator. By comparison results, it is verified that the new collimator takes advantage more than the conventional collimator. The optimum channel height and diameter of the pinhole collimator from simulation results are also proposed and designed. We finally acquired nuclear image mounting this collimator in the nuclear survey system.