Three-dimensional geometric sensitivity calculation for three-headed coincidence imaging

All major gamma camera manufacturers nowadays offer two-headed coincidence imaging with their gamma camera systems. To improve sensitivity, three-headed coincidence imaging has been proposed. In an earlier work, we investigated how the two-dimensional sensitivity varies in the field of view of such a system. In this paper, these calculations are extended to three dimensions, taking into account the finite axial length of the detector. The extension to three dimensions becomes particularly important when one acquires data in fully three-dimensional mode, without using axial septa. The three-dimensional sensitivity calculation presented here is valid for any position of the camera, such as a U-shaped configuration or a triangular configuration. We have also investigated the use of axial septa by constraining the maximum axial incidence angle.