Application of added beam filtration to intra-oral radiography.

Abstract

The vast majority of intra-oral radiographic examina­ tions use high-resolution direct-exposure films. This resolution is obtained at the expense of the increased radiation quanta needed for this type of film when compared to the screen-film systems used almost exclusively in medical and dental extra-oral radio­ graphy. The ALARA concept recommends the use of modern technology to reduce radiation exposures to the lowest possible limits while maintaining diagnostic image quality I . Current patient risk estimates from exposure to diagnostic radiation in dentistry dictate that the fastest film (currently E-speed), or other imaging technology consistent with diagnostic require­ ments, and rectangular collimation is used in intra-oral imaging Z -4. Also consistent with this policy is the use of added beam filtration to form a quasi-monochromatic X-ray beam with photon energies in the range most sensitive for the image receptor. Selective beam filtration was first suggested by Ter-Pogossiarr' in 1956 and further considered by Oosterkamp in 1961. Various heavy metal and rare earth beam filters, including yttrium, samarium, gadolinium, holmium, erbium, ytterbium and tungsten have been investigated for medical radiography. These metals filter out not only low­ energy photons from the X-ray beam but also, selec­ tively, those high-energy photons with energies above the k absorption edge of the filtering element 5 ,6 ,9 . The k absorption edges of these elements range from 17keV