Characteristics of direct and indirect active matrix flat-panel portal imagers

Recent advances in thin film transistor (TFT) technology have allowed the construction of active matrix flat-panel imagers (AMFPI) for use in both diagnostic and portal imaging. Since the design of such systems is still in the development stage, it is unclear what detector characteristics are required in order to optimize these detectors. For this reason a theoretical framework is needed. Although theories have been developed for diagnostic radiology using cascaded linear systems analysis, a theory which agrees with experimental data is lacking for megavoltage energies. In this work, we extend the theories which have been successful in describing diagnostic AMFPI detectors, and develop a general equation which can be used for both diagnostic and portal imaging, and with direct and indirect AMFPIs. We validate this theory with existing experimental data. We use the theory to determine the design requirements of AMFPIs for portal imaging, and to explore the possible advantages of a direct detection technique based on the photoconductor amorphous selenium (a-Se),.