THE DEVELOPMENT OF A NEW DIRECT DIGITAL EXTRAORAL RADIOGRAPHIC SYSTEMPROTOTYPE USING A THIN-FILM-TRANSISTOR PANEL

Objective: To develop a new method of direct digital image acquisition for extra-oral radiography. Methods: A selenium detector was combined with a thin-film transistor sensor and integrated with current techno logy 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 mu m x 139 mu m. The electrical characteristics were evaluated and image q uality was tested with a dried human mandible and half-skull phantom. The resultant images were subjectively reviewed by seven oral and maxi llofacial radiologists. Results: The prototype had a signal-to-noise r atio of 400 : 1 when the exposure was 250 x 10(-8) C/Kg. Spatial resol ution was equal to the Nyquist frequency of 3.55 cycles/mm. The images of the phantoms were considered to be of equivalent quality to conven tional screen-film images and demonstrated the normal anatomical struc tures used for clinical evaluation. Three to four images per minute we re generated with this system. Conclusion: 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 pl anned.