When performing positron emission tomography (PET) scanning and image reconstruction, a primary PET system (10) with a primary PET detector array (12) is used to image a patient or subject, and a secondary PET detector array (14) is coupled to the system at specific input points to mitigate unnecessary duplication of system components. The primary system (10) provides PET data processing and reconstruction for the secondary array (14), in addition to the first array (12). An adjustable array (120) includes radially movable detectors (122) and stationary detectors (124) with different crystal resolutions. The movable detectors (122) are alternately positioned with the stationary detectors (124) at a first radius to form a large detector ring, or are positioned at a second, smaller radius without the stationary detectors (124) to form a small detector ring.