Conventional methods of X-raying rely on photographic film technology which is quite expensive, time-consuming and inconvenient because of the necessarily applied radiation doses. Among the results of the Esprit program, the MEDID project offers an efficient alternative for digital radiography in the shape of a non-chemical flat panel detector. This solid-state device is based upon silicon technology and digital signal processing to convert X-rays into a high-quality digital image. As a major advantage, the system provides real time performance with low radiation doses. The digital images can also easily be stored and retrieved, visually enhanced as well as transmitted to other locations for remote consultation.
The new flat panel detector takes the shape of a large area of 43 cm by 43 cm consisting of an active-matrix sensor which contains 3000 x 3000 pixels. Each pixel is composed of a thin-film amorphous silicon photodiode, highly sensitive to visible light, coupled to a switch. A scintillator covers the whole matrix and converts incoming X-rays to visible light, which activates individual photodiodes to build a pixel-based image, addressed via lines and columns for signal readout.
The detector is only a few centimetres thick but has a 14-bit dynamic range. Dedicated electronics activate and control the unit. Digital data are processed using a system optimised for real time and high data throughput. Noise is reduced to a minimum thanks to the fine tuned readout amplifier.
The MEDID device generates high-quality digital images at real time speed, thus offering a great reliability in demanding work environments. As a result, important costs can be saved by fast and accurate diagnosis. The project was set up by Thomson Tubes Electroniques in collaboration with Siemens.