[Characterization of the response of hexagonal parallel-hole collimators of scintillation cameras]

This paper presents a formulation of the frequency response of hexagonal parallel-hole collimator scintillation cameras. To describe this response, we propose an equation determined semi-empirically from a great number of simulations. The utility of the equation is that it enables the simple calculation of the response from collimator characteristics by taking into account the collimator's hexagonal structure. Because the equation does not assume translation invariance, the results can be directly compared with experimental measurements obtained with a point source. It is particularly interesting for collimators with large holes, like the medium-resolution ones used for high-energy radiation. Quality control and physical performance measurements are thus facilitated for this kind of collimator. Also, we present a new parameter that gives a quantitative assessment of the importance of partition penetration. This parameter is measured directly from the collimator frequency response. It has been studied by simulation, taking into account gamma photon attenuation in collimator partitions. The experimental measurements that have been made are in accord with the proposed equations.