Flat panel detector (FPD) technology for X-ray detection and imaging advanced rapidly in the last decade fueled by continuous improvements in large area, amorphous silicon (a-Si) thin film transistors (TFT) arrays and innovations in deposition techniques for scintillators and photoconductors. Amorphous selenium (a-Se) is a direct X-ray to charge converter material whose properties as photoconductor as well as semiconductor make it suitable for both static and dynamic imaging. In this paper we will present a series of a-Se based X-ray detectors, will characterize their defining parameters and will describe the most recent advances in materials and low noise application specific integrated circuits (ASIC) conducive to their superior performance in real-time imaging applications.