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Chest Radiography with a Flat-Panel Detector: Image Quality with Dose Reduction after Copper Filtration¹

¹ From the Department of Diagnostic Radiology, University Hospital of Regensburg, Franz-Josef-Strauss-Allee 11, 93042 Regensburg, Germany (O.W.H., I.B., N.Z., S.F.); Department of Radiology, UCSD Medical Center, San Diego, Calif (C.B.S.); Department of Radiology, Hospital Hohe Warte, Bayreuth, Germany (M.S.); and Department of Radiology, Ulm Army Hospital, Ulm/Donau, Germany (M.V.). From the 2004 RSNA Annual Meeting. Received October 9, 2004; revision requested December 21; revision received February 6, 2005; accepted March 7. Address correspondence to O.W.H. (e-mail: o.hamer{at}gmx.de).

PURPOSE: 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.

MATERIALS AND 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-µGy 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.

CONCLUSION: 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.

© RSNA, 2005