The invention relates to a system for imaging an object in an x-ray imaging mode and in a gamma imaging mode. A radiation detector (1) of the system comprises a conversion unit (202) including a plurality of detector pixels (2061, . . . ,M) and generating for each detection event a detection signal indicative of an energy of the event, and a counting unit (203) including for each detector pixel (2061, . . . ,M) a plurality of comparators (209i; 1, . . . ,N) and associating each detection event to one of a plurality of predetermined energy bins based on the detection signals using the comparators (209i; 1, . . . ,N). In the x-ray imaging mode, the comparators (209i; 1, . . . ,N) of one pixel (2061, . . . ,M), and in the gamma imaging mode, the comparators (209i; 1, . . . ,N) of several pixels (2061, . . . ,M) are available for the association so that more energy bins are available in the gamma imaging mode than in the x-ray imaging mode.