title: Evaluating scintillators used in radiation detectors of medical imaging systems by the effective fidelity index method.
abstract: OBJECTIVE
  The performance of medical X-ray image receptors depends: (1) on the scintillator light emission efficiency; and (2) on the compatibility of the scintillator light spectrum with the spectral sensitivity of the light detector (film, photocathode, or photodiode), employed in conjunction with the scintillator. In this study, a scintillator performance measure, the effective fidelity index (EFI), is defined as function of both the scintillator light emission efficiency and spectral compatibility.
  
  
  METHODS
  CsI:Na, Gd2O2S:Tb and La2O2S:Tb scintillators were employed in the form of phosphor screens prepared in our laboratory with various coating thicknesses. The screens were irradiated with X-rays employing tube voltages ranging between 50-120 kVp.
  
  
  RESULTS
  The EFI performance of CsI:Na was found to increase with screen coating thickness and it was best when combined with the orthochromatic film or the ES/20 photocathode. Gd2O2S:Tb showed peak EFI performance at 70 mg/cm2 coating thickness and it was well combined with the light detectors considered.
  
  
  CONCLUSIONS
  In accordance with our results, CsI:Na may be employed in radiography when adequately protected against humidity. Gd2O2S:Tb suitability for conventional imaging was verified and it was found that it may be useful in all types of digital imaging. La2O2S:Tb could also be used in digital detectors of imaging applications demanding medium X-ray tube voltages.
authors.affiliation: Department of Medical Instrumentation Technology, Technological Educational Institution of Athens, Greece.
authors.forename: I
authors.initials: I
authors.lastname: Kandarakis
authors.forename: D
authors.initials: D
authors.lastname: Cavouras
authors.forename: P
authors.initials: P
authors.lastname: Prassopoulos
authors.forename: E
authors.initials: E
authors.lastname: Kanellopoulos
authors.forename: C D
authors.initials: CD
authors.lastname: Nomicos
authors.forename: G S
authors.initials: GS
authors.lastname: Panayiotakis
mesh_terms: D015902:Gamma Cameras; D008027:Light; D008722:Methods; D011859:Radiography / Q000295:instrumentation* / Q000592:standards