Investigation of lag and ghosting in amorphous selenium flat-panel x-ray detectors

Our goal is to understand the temporal response of amorphous selenium (a-Se) x-ray imaging detectors. The temporal response caused by charge trapping and release gives rise to the imaging properties of lag and ghosting. These imaging properties depend on both the design and operational parameters of the detectors as well as the material properties of a-Se. Our approach was to measure the x-ray photocurrent of electroded a-Se detectors as a function of x-ray exposure and correlate these measurements with an experimental investigation of charge trapping by use of the "time-of-flight" method. These experimental results are compared with models based on previously published values of material properties such as electron and hole trapping and recombination cross-sections. The resulting model can be used to predict lag and ghosting in radiographic and fluoroscopic flat panel detectors. We also investigated the effect of charge trapping between the pixel electrodes of an a-Se flat-panel detector on lag and ghosting. Our method for quantitative evaluation of lag and ghosting in a-Se will facilitate the optimization of imaging performance. This is achieved by determining the combination of materials properties, system design and operational parameters which minimize artifacts arising from either lag or ghosting in a-Se flat-panel detectors.