A control system (54) for an X-ray scanner, the system comprising an input (Din) arranged to receive an input signal identifying which of a plurality of electron emitters (25) is to be active, and to produce a plurality of outputs (HVout0 ... HVout 31) each arranged to control operation of one of the emitters. Each of the outputs can be in a first state arranged to activate its respective emitter, and a second state arranged to de-activate said emitter. The system further comprising blanking means (606, BLA) arranged to fix all of the outputs in the second state irrespective of which state the input signal indicates they should nominally be in.
