AbstractID: 9750 Title: Lag Mechanism in A-Se Radiation Detectors
Amorphous selenium (a-Se) x-ray detector research and development has been ongoing for several decades due to its favorable intrinsic
properties that make it a good photodetector. It has been used in commercial systems for general radiography and mammography, and has been
under consideration for use in fluoroscopy and megavoltage CT (MVCT). In recent years, a-Se active matrix flat panel imagers (AMFPIs) have
been developed for medical imaging. Amorphous selenium detectors do however suffer from a temporal lag effect, which is due to residual signal
from previous exposures, and can be seen in subsequently acquired dark images. The lag generates artifacts, which result in reduced contrast in
the images subsequently produced by the detector. To date, no model has been developed to explain this phenomenon for the externally biased
detector. A theoretical approach to describe the mechanism of lag in AMFPIs has been derived. Differential equations characterizing the carrier
photogeneration, trapping, and recombination have been used to derive an analytical expression for the temporal a-Se AMFPI detector sensitivity
response. We have fitted this theoretical model to the experimentally measured lag data for 81 kvp x-rays and a frame time of 7.2 s by using a
Monte Carlo method.