Investigation of strategies to achieve optimal DQE performance from indirect detection, active matrix flat-panel imagers (AMFPIs) through novel pixel amplification architectures

The numerous merits of x-ray imagers based on active matrix, flat-panel array technology have led to their introduction in a wide variety of x-ray imaging applications. However, under certain conditions, the performance of direct and indirect detection AMFPIs is significantly limited by the relatively modest ratio of signal to noise provided by conventional systems. While substantial reduction in the additive noise of such systems is difficult, significant enhancement of signal can be achieved through the incorporation of an amplification circuit in each pixel. In addition, innovative photodiode structures can be incorporated into indirect detection designs to enhance optical signal collection efficiency. In this paper, an investigation of these strategies, involving the design, fabrication and performance evaluation of a variety of novel, small area, indirect detection arrays, is described. Each prototype array incorporates innovative features, such as continuous photodiodes and single-stage and dual-stage in-pixel amplifiers, that are designed to provide insight into promising avenues for achieving significant signal-to-noise enhancement. This information will assist in the realization of a next generation of highly-optimized AMFPI pixel architectures whose DQE performance will be limited only by x-ray noise and x-ray converter properties under a very wide range of conditions. In this paper, the design and operation of the present prototype arrays are described and initial performance results are reported. In addition, the benefits of significant improvements to the signal-to-noise properties of AMFPIs are illustrated through cascaded systems calculations of the DQE performance of hypothetical systems.