A photomultiplier detector cell for tomography includes a detector unit and a readOUT unit. The detector unit is configured to generate a digitized detect signal in response to receives light having a certain range of wavelength. The readOUT unit is configured to generate an output signal corresponding to the detect signal generated by the detector unit and to transmit the output signal to an external circuit. The readOUT unit is configured to transmit the output signal to the external circuit right after the detect signal is received.