X-ray imaging using amorphous selenium: inherent spatial resolution

This is a theoretical study of the inherent spatial resolution of the latent image on the surface of an amorphous selenium (a-Se) plate used for diagnostic x-ray imaging. The following effects are considered: (A) ranges of primary photoelectrons; (B) reabsorption of K fluorescence; (C) reabsorption of Compton scattered photons; (D) diffusion; (E) the geometric effect due to oblique incidence of x rays; (F) electrostatic effect; and (G) the space charge effect. The modulation transfer function of a-Se in the diagnostic x-ray energy range has been estimated. In conclusion, (A) and (E) are the main factors limiting the resolution, and for diagnostic x rays, the inherent spatial resolution of a-Se plates is much better than that of CsI layers used in x-ray image intensifiers.