Abstract: Described here are tileable block detectors for use in nuclear medicine applications, such as in positron emission tomography (“PET”] systems and positron emission mammography (“PEM”] systems. The block detectors described here are four-side tileable such that seamless arrays of block detectors can be constructed for use in PET or PEM systems. When so arrayed, the block detectors allow for a full-size seamless detector that achieves full coverage of an object (e.g., a gently immobilized breast), improves data collection, and enables high-resolution imaging with a significantly lower radiation dose than with other currently available PEM systems.