A new pinhole aperture design for single photon imaging is introduced whose distinctive feature is a channeled aperture. This allows greater attenuation near the pinhole aperture which is especially important when imaging 131I with its medium and high energy emissions. Point source response functions were simulated for pinhole inserts with different pinhole diameters (0.4-2.0 mm diameter) and channel heights (0.1-3.0 mm) with acquisition parameters appropriate for 131I brain tumor imaging. A photon transport simulation code was used to comprehensively model photon transport and detection. Tradeoff curves between resolution and sensitivity suggest that varying pinhole diameter and channel height to achieve higher resolution at the expense of decreased sensitivity may be advantageous for imaging tumors with intratumoral administration of 131I radiolabeled monoclonal antibodies.