title: Chest radiography with a flat-panel detector: image quality with dose reduction after copper filtration.
abstract: OBJECTIVE
  To compare image quality and estimated dose for chest radiographs obtained by using a cesium iodide-amorphous silicon flat-panel detector at fixed tube voltage and detector entrance dose with and without additional 0.3-mm copper filtration.
  
  
  METHODS
  The study was approved by the institutional ethics committee. All prospectively enrolled patients signed the written consent form. Chest radiographs in two projections were acquired at 125-kVp tube voltage and 2.5-microGy detector entrance dose. The experimental group (38 patients) was imaged with 0.3-mm copper filtration; the control group (38 patients) was imaged without copper filtration. An additional 12 patients were imaged with and without copper filtration and served as paired subject-controls. Three readers blinded to group and clinical data independently evaluated the radiographs for image quality on a digital display system. Twelve variables (six for each radiographic projection) were assigned scores on a seven-point ordinal scale. Scores between experimental and control groups were compared: Logistic regression analysis and Mann-Whitney U test were used for unpaired patients; and Wilcoxon and McNemar test, for paired patients. In all, 72 comparisons were determined (36 [12 variables x three readers] for unpaired patients and 36 for paired patients). In a phantom study, radiation burden of experimental protocol was compared with that of control protocol by using Monte Carlo calculations.
  
  
  RESULTS
  For 70 of 72 comparisons, digital radiographs obtained with copper filtration were of similar image quality as radiographs obtained without copper filtration (P = .123 to P > .99). For two of 72 comparisons, one observer judged the experimental protocol superior to the control protocol (P = .043, P = .046). Patient dose reduction estimated with Monte Carlo calculations was 31%. Use of copper filtration increased exposure times by 48% for posteroanterior views and by 34% for lateral views.
  
  
  CONCLUSIONS
  Subjectively equivalent chest radiographic image quality was found with estimated 30% dose reduction after addition of 0.3-mm copper filtration with flat-panel cesium iodide-amorphous silicon technology.
authors.affiliation: Department of Diagnostic Radiology, University Hospital of Regensburg, Franz-Josef-Strauss-Allee 11, 93042 Regensburg, Germany. o.hamer@gmx.de
authors.forename: Okka W
authors.initials: OW
authors.lastname: Hamer
authors.forename: Claude B
authors.initials: CB
authors.lastname: Sirlin
authors.forename: Michael
authors.initials: M
authors.lastname: Strotzer
authors.forename: Ingitha
authors.initials: I
authors.lastname: Borisch
authors.forename: Niels
authors.initials: N
authors.lastname: Zorger
authors.forename: Stefan
authors.initials: S
authors.lastname: Feuerbach
authors.forename: Markus
authors.initials: M
authors.lastname: Völk
mesh_terms: D002586:Cesium; D003300:Copper; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007454:Iodides; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011446:Prospective Studies; D011829:Radiation Dosage; D011856:Radiographic Image Enhancement / Q000295:instrumentation*; D013902:Radiography, Thoracic / Q000295:instrumentation*; D012189:Retrospective Studies; D012825:Silicon; D018709:Statistics, Nonparametric; D014963:X-Ray Intensifying Screens
chemical_list: D007454:Iodides; D002586:Cesium; D003300:Copper; C040050:cesium iodide; D012825:Silicon