title: Light output measurements and computational models of microcolumnar CsI scintillators for x-ray imaging.
abstract: OBJECTIVE
  The authors report on measurements of light output and spatial resolution of microcolumnar CsI:Tl scintillator detectors for x-ray imaging. In addition, the authors discuss the results of simulations aimed at analyzing the results of synchrotron and sealed-source exposures with respect to the contributions of light transport to the total light output.
  
  
  METHODS
  The authors measured light output from a 490-μm CsI:Tl scintillator screen using two setups. First, the authors used a photomultiplier tube (PMT) to measure the response of the scintillator to sealed-source exposures. Second, the authors performed imaging experiments with a 27-keV monoenergetic synchrotron beam and a slit to calculate the total signal generated in terms of optical photons per keV. The results of both methods are compared to simulations obtained with hybridmantis, a coupled x-ray, electron, and optical photon Monte Carlo transport package. The authors report line response (LR) and light output for a range of linear absorption coefficients and describe a model that fits at the same time the light output and the blur measurements. Comparing the experimental results with the simulations, the authors obtained an estimate of the absorption coefficient for the model that provides good agreement with the experimentally measured LR. Finally, the authors report light output simulation results and their dependence on scintillator thickness and reflectivity of the backing surface.
  
  
  RESULTS
  The slit images from the synchrotron were analyzed to obtain a total light output of 48 keV-1while measurements using the fast PMT instrument setup and sealed-sources reported a light output of 28 keV-1. The authors attribute the difference in light output estimates between the two methods to the difference in time constants between the camera and PMT measurements. Simulation structures were designed to match the light output measured with the camera while providing good agreement with the measured LR resulting in a bulk absorption coefficient of 5 × 10-5μm-1.
  
  
  CONCLUSIONS
  The combination of experimental measurements for microcolumnar CsI:Tl scintillators using sealed-sources and synchrotron exposures with results obtained via simulation suggests that the time course of the emission might play a role in experimental estimates. The procedure yielded an experimentally derived linear absorption coefficient for microcolumnar Cs:Tl of 5 × 10-5μm-1. To the author's knowledge, this is the first time this parameter has been validated against experimental observations. The measurements also offer insight into the relative role of optical transport on the effective optical yield of the scintillator with microcolumnar structure.
authors.affiliation: Royal Institute of Technology (KTH), Stockholm SE-100 44, Sweden.
authors.forename: Peter
authors.initials: P
authors.lastname: Nillius
authors.affiliation: Royal Institute of Technology (KTH), Stockholm SE-100 44, Sweden.
authors.forename: Wlodek
authors.initials: W
authors.lastname: Klamra
authors.affiliation: National Centre for Nuclear Research, Otwock 05-400, Poland.
authors.forename: Pawel
authors.initials: P
authors.lastname: Sibczynski
authors.affiliation: Division of Imaging, Diagnostics, and Software Reliability, Office of Science and Engineering Laboratories, Center for Devices and Radiological Health, FDA, Silver Spring, Maryland 20993.
authors.forename: Diksha
authors.initials: D
authors.lastname: Sharma
authors.affiliation: Royal Institute of Technology (KTH), Stockholm SE-100 44, Sweden.
authors.forename: Mats
authors.initials: M
authors.lastname: Danielsson
authors.affiliation: Division of Imaging, Diagnostics, and Software Reliability, Office of Science and Engineering Laboratories, Center for Devices and Radiological Health, FDA, Silver Spring, Maryland 20993.
authors.forename: Aldo
authors.initials: A
authors.lastname: Badano
mesh_terms: D002586:Cesium; D003198:Computer Simulation; D004583:Electrons; D007454:Iodides; D008027:Light; D008962:Models, Theoretical; D009010:Monte Carlo Method; D017785:Photons; D011859:Radiography / Q000295:instrumentation* / Q000379:methods*; D012588:Scintillation Counting / Q000295:instrumentation* / Q000379:methods; D013793:Thallium; D014965:X-Rays
chemical_list: D007454:Iodides; D002586:Cesium; D013793:Thallium; C040050:cesium iodide
keywords: Absorption coefficient; Biological material, e.g. blood, urine; Haemocytometers; Cameras; CsI; Electron multipliers; Emission spectra; Image sensors; Measurement of nuclear or x-radiation; Monte Carlo methods; Monte Carlo simulations; Photomultipliers; phototubes and photocathodes; Photons; Plates or blocks in which tracks of nuclear particles are made visible by after-treatment, e.g. using photographic emulsion, using mica; Radiography; Scintillation detectors; Spatial resolution; Tubes for determining the presence, intensity, density or energy of radiation or particles; Visible spectra; X-ray imaging; blur; caesium compounds; diagnostic radiography; light output; light transport; photomultipliers; scintillator; solid scintillation detectors; thallium; the detector being a crystal; the detector being a liquid; the detector being made of plastics; with semiconductor detectors