Chest radiography with a flat-panel detector:: Image quality with dose reduction after copper filtration

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-mu Gy 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. (c) RSNA, 2005.