A radiation detector includes a detector block, cables, connectors, and circuit substrates. The detector block has a plurality of radiation detector modules arranged in a slice direction. The cables extend in the slice direction and configured to receive signals from the radiation detector modules of the detector block. The connectors are associated with the cables, respectively, and are spaced, one from another, in the slice direction. The circuit substrates are configured to receive signals via the connectors from the radiation detector modules of the detector block.