In this thesis, the x-ray time-of-flight (TOF) method was developed for the investigation of ghosting (i.e. radiation-induced changes of sensitivity) in amorphous selenium (a-Se) based real-time flat-panel imagers (FPIs). The method consists of irradiating layers of a-Se with short x-ray pulses. From the current generated in the a-Se layer, ghosting is quantified and the ghosting parameters (charge carrier generation rate, and carrier lifetimes and mobilities) are assessed. The x-ray TOF method is novel in that (1) ghosting and ghosting parameters can be measured simultaneously, (2) transport of holes and electrons can be isolated and (3) the method is applicable to practical a-Se layers with blocking contacts. This work provides the basis for understanding ghosting in a-Se based FPIs thus making them fit for high frame-rate and high dose x-ray imaging applications.