The development of a new direct digital extra-oral radiographic system prototype using a thin-film transistor panel

To develop a new method of direct digital image acquisition for extra-oral radiography. A selenium detector was combined with a thin-film transistor sensor and integrated with current technology for computed radiography in a system named Direct Radiography (DR). The effective image area of the prototype is 178 mm x 213.5 mm, and consists of a 1280 x 1536 pixel matrix with a pixel pitch of 139 microns x 139 microns. The electrical characteristics were evaluated and image quality was tested with a dried human mandible and half-skull phantom. The resultant images were subjectively reviewed by seven oral and maxillofacial radiologists. The prototype had a signal-to-noise ratio of 400:1 when the exposure was 250 x 10(-8) C/Kg. Spatial resolution was equal to the Nyquist frequency of 3.55 cycles/mm. The images of the phantoms were considered to be of equivalent quality to conventional screen-film images and demonstrated the normal anatomical structures used for clinical evaluation. Three to four images per minute were generated with this system. The DR system has an X-ray sensitivity comparable with a 400-speed film-screen system and appears suitable for clinical radiography. Further evaluation is therefore planned.