Usefulness of reduced image display size in softcopy reading: evaluation of lung nodules in chest screening

The purposes of the present study were to investigate the impact of viewing size on soft-copy diagnosis for detecting abnormalities on digital chest radiographs and to verify the usefulness of reduced digital chest radiography.

Receiver-operating characteristic (ROC) and localized ROC (LROC) analysis of clinical images was performed using the standard digital image database of the Japanese Radiation Technology Society. A total of 30 images with and 20 images without nodule samples were extracted randomly from the database and used for ROC analysis. A total of 100 images were prepared for observation of reduced and nonreduced images. Observers' viewing images were adjusted as nonreduced size (large, 30 x 30 cm) and reduced size (small, 15 x 15 cm).

The estimated mean areas under the LROC curves were 0.665 +/- 0.071 for large-size images and 0.669 +/- 0.087 for small-size images. However, no statistically significant difference was found between the two groups (P = .823). The viewing time of small-size images (1201.4 seconds) was significantly shorter than that of large-size images (1719.7 seconds). A statistically significant difference was also found in viewing times between reduced and nonreduced digital images with Wilcoxon's signed-rank test (P < .05).

This study provided important information that there was a statistically significant difference in viewing times between reduced and nonreduced digital chest radiographic images, whereas no significant difference was found in areas under the LROC curves for the accuracy of diagnosis between the two groups. However, the double-check method for chest x-ray screening would be done efficiently by changing the viewing size to improve the specificity of diagnosis.