A method of reading out data in a radiation detector having pixels and associated readout circuits, which each have a register. After the pixels detect radiation, data indicative of the radiation is stored in the register(s) of each readout circuit, each time during a plurality of data acquisition periods. Data is read out from the register(s) of each readout circuit, each time during a plurality of readout periods. Each readout period follows a data acquisition period, and each readout period being either a low energy readout period or a high energy readout period. Only data from a single register of each readout circuit indicative of radiation energy above a low energy level is read out during each low energy readout period. Data indicative of radiation energy above a high energy level, higher than the low energy level, is read out during each high energy readout period.