X-ray CT apparatus, radiation detector and method for reading out electric signals of a radiation detector

An X-ray CT apparatus comprises an X-ray generating unit and a radiation detector . The radiation detector includes a plurality of detecting elements put in two-dimensional positions and separated into a plurality of readout blocks, a readout circuit for reading out electric signals from the detecting elements in the respective readout blocks, a switch circuit for switching the electric signals read out to the readout circuit from the detecting elements at the readout blocks and a switch control circuit for controlling the switch circuit so as to read out electric signals with time-sharing from corresponding detecting elements in a common readout block of the readout blocks to the readout circuit and to read out corresponding electric signals in parallel from at least two of the detecting elements to the readout circuit, the two being in different readout blocks each other.