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Detection of Subtle Undisplaced Rib Fractures in a Porcine Model: Radiation Dose Requirement—Digital Flat-Panel versus Screen-Film and Storage-Phosphor Systems¹

¹ From the Department of Clinical Radiology (K.L., C.S., S.D., D.W., H.L., T.M.B., W.H.) and Institute of Experimental Biomechanics (P.B.), University of Munster, Albert-Schweitzer-Strasse 33, D-48129 Munster, Germany. Received April 1, 2002; revision requested June 11; revision received July 9; accepted August 16. Address correspondence to K.L. (e-mail: lud@uni-muenster.de).

PURPOSE: To compare a large-area direct read-out flat-panel detector radiography system with screen-film and storage-phosphor systems with regard to detection of subtle undisplaced rib fractures and to assess the diagnostic performance of the flat-panel system with decreasing exposure level.

MATERIALS AND METHODS: Subtle fractures were created artificially in 100 of 200 porcine rib specimens. Specimens were enclosed in containers of water to generate absorption and scatter radiation conditions similar to those of a human chest wall. Imaging was performed with flat-panel, screen-film, and storage-phosphor systems with conditions that were exactly matched. Different exposure levels equivalent to speed classes (S) of 400, 800, 1,600, and 6,400 were used. All images were independently assessed for the presence of fracture by three radiologists with a five-level confidence scale. Receiver operating characteristic (ROC) analysis was performed for a total of 4,200 observations (600 for each imaging system and exposure level). Diagnostic performance was estimated with area under the ROC curve (A_z). Significance of differences in diagnostic performance was tested with analysis of variance.

RESULTS: ROC analysis yielded mean A_z values for the flat-panel system of 0.879 (S = 400), 0.833 (S = 800), 0.765 (S = 1,600), and 0.576 (S = 6,400). A_z values were 0.834 (S = 400) for the screen-film system and 0.789 (S = 400) and 0.729 (S = 800) for the storage-phosphor system. Analysis of variance revealed significant differences in diagnostic performance between various combinations of imaging system and exposure levels (P < .05).

CONCLUSION: The flat-panel system is superior to the screen-film and storage-phosphor systems for detection of subtle undisplaced rib fractures at clinical exposure settings (eg, S = 400). With the flat-panel system, radiation dose can be reduced by 50% to achieve diagnostic performance comparable to that of a speed class 400 screen-film system.

© RSNA, 2003

Index terms: Experimental study • Radiations, measurement • Radiography, digital • Radiography, flat panel • Radiography, comparative studies • Ribs, fractures, 471.41

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