CT Scanner Component: High Voltage Generator

To Produce and maintain the desired x ray flux output, the voltage and current to the x ray tube must be kept at a constant or desired level. Unfortunately, the voltage of the power fluctuates sinusoidally from negative to positive relative to the front. This is undesirable for two reason :

1. If cathode voltage becomes positive relative to anode, electron emitted from the hot anode will accelerate toward the cathode, causing the cathode filament to age prematurely and generate undesired x ray photons(located significant off the x ray focal spot)
2. High fluctuation of the voltage causes significant difficulties in the calibration and data conditioning for the CT systems. Note that the energy spectrum of the x ray flux is linked closely to the voltage potential across the cathode and anode. When significant variation exist in the power supply voltage, the x ray spectrum changer constantly from view to view. This makes some of correction process, such as beam hardening, nearly impossible.  To ensure adequate image quality and prevent premature x ray tube failure, the power supply to the x ray is typically rectified and additional efforts are made to ensure the voltages is as close to a constant as possible ( to simulate a dc power supply). The voltage generator from single phase rectified typically has ripple of 100 %. Ripple is defined as t he peaks to valley voltage over peak voltage