  Thallium-doped cesium iodide (CsI(Tl)) screens are widely used in X-ray
imaging devices because of the columnar structure of CsI(Tl) layer, but few
reports focus on the optical role of the substrate in the screen system. In
this paper, four substrates including fused silica (SiO2), silver-film coated
SiO2, graphite (C) and fiber optic plate (FOP) are used to fabricate CsI(Tl)
screens by thermal evaporation. Their imaging performance is evaluated by
relative light output (RLO), modulation transfer function (MTF), normalized
noise power spectrum (NNPS) and noise equivalent quanta (NEQ). The results
reveal that although CsI(Tl) film on graphite plate yields images with the
lowest light output, it presents relatively higher spatial resolution and
better signal-to-noise characteristics. However, films on SiO2 plate obtain low
MTF but high NNPS curves, whether or not coated with silver film. Furthermore,
scintillation screens on FOP have bright images with low NNPS and high NEQ, but
have the lowest MTF. By controlling the substrate optical features, CsI(Tl)
films can be tailed to suit a given application.
