Performance assessment of CsI(Tl) screens on various substrates for X-ray imaging

摘要

Thallium-doped cesium iodide (CsI(Tl)) screens are widely used in X-rayimaging devices because of the columnar structure of CsI(Tl) layer, but fewreports focus on the optical role of the substrate in the screen system. Inthis paper, four substrates including fused silica (SiO2), silver-film coatedSiO2, graphite (C) and fiber optic plate (FOP) are used to fabricate CsI(Tl)screens by thermal evaporation. Their imaging performance is evaluated byrelative light output (RLO), modulation transfer function (MTF), normalizednoise power spectrum (NNPS) and noise equivalent quanta (NEQ). The resultsreveal that although CsI(Tl) film on graphite plate yields images with thelowest light output, it presents relatively higher spatial resolution andbetter signal-to-noise characteristics. However, films on SiO2 plate obtain lowMTF 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, buthave the lowest MTF. By controlling the substrate optical features, CsI(Tl)films can be tailed to suit a given application.