I. Introduction
Compact high-resolution gamma cameras are very useful in applications like small animal pinhole single photon emission computed tomography (SPECT) imaging. With small detectors one can place many pinhole cameras around the object of investigation, resulting in a high counting sensitivity [1]–[9]. Other applications of compact gamma cameras include planar gamma camera imaging [10]–[12], radiation monitoring (e.g., [13]), tumor surgery [14], and autoradiography [15].