Real-time x-ray imaging with flat panels

To provide real-time x-ray imaging, industry relies almost entirely on the combination of the x-ray image intensifier and the high-performance television camera. Although these devices have been pushed to remarkable degrees of performance, they remain complex electro-optical assemblies with significant built-in errors, instabilities and degradation mechanisms. We describe a replacement for these systems utilizing as a sensor a large array of amorphous silicon photodiodes and thin-film switching transistors. Specifically, the equipment described is a replacement for a 9-inch dual-mode x-ray image intensifier with a high-performance 2000-line digital tv camera capable of operating in both real-time video radioscopic and highperformance radiographic modes. The sensor-panel imager consists of three units: 1) a sensor assembly including a 1536x1920 pixel sensor, an x-ray scintillator and all electronics necessary to drive the sensor panel, collect the readout charge, convert the signal to 12-bit digital data and format the data into a serial data stream for transmission, 2) a controller which receives configuration and timing commands from the world, an image processor which corrects the pixel data for variations in dark level and sensitivity and interpolates dead pixels all in real time and provides digital and analog video data and a set of system interface signals out, and 3) a power supply module. In the radioscopic mode, this imager produces x-ray images at 30 frames per second with a resolution of just under 2 lp/mm. In the radiographic mode, five frames per second may be produced with nearly 4 lp/mm resolution. Doses from 1 mu R to 10mR per frame can be accommodated. Unlike x-ray image intensifiers, this system has no geometric distortion or performance rolloff at the edges, requires no high voltage and has no susceptibility to external magnetic fields. Unlike CCD x-ray sensors, this sensor tolerates accumulated x-ray exposures at the megarad level. Additional work is underway to develop sensors with larger area and higher resolution. Current status on these extensions will be reported. Others have reported on the development of amorphous silicon sensors suitable for replacement of photographic film in radiography. The present work extends this to real-time applications thereby promising the availability of the digital flat-panel technology as a universal x-ray imaging medium.