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Digital Storage Phosphor Chest Radiography: An ROC Study of the Effect of 2K versus 4K Matrix Size on Observer Performance¹

¹ From the Department of Radiology, Stanford University Medical Center, 300 Pasteur Dr, S072A, Stanford, CA 94305-5105. Received February 23, 2000; revision requested April 9; revision received June 12; accepted July 25. Supported in part by a grant from Fuji Medical Systems. Address correspondence to A.N.L. (e-mail: aleung@stanford.edu).

PURPOSE: To compare observer performance in the detection of abnormalities on 1,760 x 2,140 matrix (2K) and 3,520 x 4,280 matrix (4K) digital storage phosphor chest radiographs.

MATERIALS AND METHODS: One hundred sixty patients who underwent dedicated computed tomography (CT) of the thorax were prospectively recruited into the study. Posteroanterior and lateral computed radiographs of the chest were acquired in each patient and printed in 2K and 4K formats. Six radiologists independently analyzed the hard-copy images and scored the presence of parenchymal (opacities 2 cm, opacities >2 cm, and subtle interstitial), mediastinal, and pleural abnormalities on a five-point confidence scale. With CT as the reference standard, observer performance tests were carried out by using receiver operating characteristic (ROC) analysis.

RESULTS: Analysis of averaged observer performance showed 2K and 4K images were equally effective in detection of all three groups of abnormalities. In the detection of the three subtypes of parenchymal abnormalities, there were no significant differences in averaged performance between the 2K and 4K formats (area below ROC curve [A_z] values: opacities 2 cm, 0.62 ± 0.056 [standard error] and 0.59 ± 0.045; opacities >2 cm, 0.86 ± .025 and 0.85 ± 0.030; subtle interstitial abnormalities, 0.73 ± 0.041 and 0.72 ± 0.041). Averaged performance in detection of mediastinal and pleural abnormalities was equivalent (A_z values: mediastinal, 0.70 ± 0.046 and 0.73 ± 0.033; pleural, 0.85 ± 0.032 and 0.86 ± 0.033).

CONCLUSION: Observer performance in detection of parenchymal, mediastinal, and pleural abnormalities was not significantly different on 2K and 4K storage phosphor chest radiographs.

Index terms: Radiography, comparative studies, 60.1215 • Radiography, digital, 60.1215 • Radiography, storage phosphor, 60.1215 • Receiver operating characteristic (ROC) curve • Thorax, radiography, 60.1215

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