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The goal of the present work is to develop a large area, flat-panel solid-state detector for both digital radiography and fluoroscopy. The proposed detector employs a photoconductive layer of amorphous selenium (a-Se) to convert x rays into charge. The charge image formed by the a-Se layer is electronically read out in situ using a two dimensional array of thin film transistors (TFTs), or active matrix. Since the active matrix readout is capable of producing x-ray images in real-time, it can potentially be applied in both radiography and fluoroscopy. In this paper, the imaging performance of this concept is investigated using a prototype x-ray imaging detector. The designs for the active matrix, the peripheral electronic circuits, and the image acquisition system are described. Measurements of x-ray imaging properties of the prototype detector, i.e., x-ray sensitivity, presampling modulation transfer function (MTF), and noise power spectrum (NPS), were performed, and from which the spatial frequency dependent detective quantum efficiency (DQE) of the prototype was derived. The experimental results are in agreement with the results of our theoretical analysis. The factors affecting the imaging performance and methods of improvement in the future are discussed.

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Future imaging techniques will be capable of high image quality, fast acquisition, compactness, and versatile operation. A flat-panel imager that is expected to achieve these goals is under development. It consists of a thin layer of amorphous selenium that converts x rays directly to an electric charge and a thin-film electronic circuit, or active matrix, to read out the electronic signal directly to a computer host. The advantages of amorphous selenium include high resolution and low noise without loss of signal strength. The advantages of the active matrix are real-time readout, flexible design parameters, and compactness of the readout structures. A prototype of this imager has been built and operated, and initial images (of an x-ray test bar pattern and a hand phantom) have been acquired. Although the prototype was built to test scientific principles and many possibilities for optimization remain, the images already possess the quality necessary for many radiographic procedures. A large range of current and new applications exist for this imager.

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