For boosting/blanking the filament current of a cathode of an X-ray tube the temporal variation of the tube current of the X-ray tube is measured and stored in a first memory. Then an iterative boosting/blanking is performed wherein the boosting/blanking current is applied to the filament for a short time interval (Δt), based on the stored temporal variation of the tube current the tube current after the short time interval (ΔT) is determined, and the tube current is stored in a second memory. Based on the stored temporal variation of the tube current it is determined if the tube current (IE) is less than a target value (IE2) thereof, and if so, the boosting/blanking current is applied to the filament for an additional time interval (Δt), else it is determined that the tube current (IE) is equal to the target value (IE2). Therefore, the tube current (IE) after each time interval (Δt) is known (may be determined from the tube current data stored in the second memory)such that the iterative boosting/blanking may be interrupted anytime.