Investigation of optimal viewing size for detecting nodular ground-glass opacity on high-resolution computed tomography with cine-mode display.

We evaluated the effect of the displayed image sizes on observers' ability to detect nodular ground-glass opacity (n-GGO) on CT and investigated the optimal viewing size for soft-copy reading at CT screening for lung cancer. A total of 46 patients' high-resolution computed tomography (HRCT) images (22 patients with one GGO; 24 without GGO) were displayed on a monochromatic liquid crystal display monitor at a resolution of 1,200 × 1,600. HRCT was presented on the screen with cine-mode display. We compared two viewing sizes (original size, i.e., the image displayed with a zoom factor of 1 in which each pixel value in the image is displayed as one pixel on the display: 13 cm × 13 cm; fit size, i.e., by zooming the captured image until it occupies the entire screen: 30 cm × 30 cm) in terms of radiologists' performance for detecting n-GGO on HRCT and the viewing times required for soft-copy reading decisions. Observer performance was analyzed in terms of the receiver operating characteristic (ROC) curve. A statistically significant improvement was found with the original size in the average area-under-the-ROC curve values for the accuracy of diagnosis and the viewing times compared to the fit size (P < 0.05). The original size with cine-mode display leads to increased lung GGO detection at CT screening for lung cancer, and the reduced time spent performing the diagnosis offers cost savings.

Investigation of optimal display size for detecting ground-glass opacity on high resolution computed tomography using a new digital contrast-detail phantom.

The purpose of this study was to clarify the relationship between display sizes of high resolution computed tomography (HRCT) images for detecting ground-glass opacity (GGO) and observer performance using a digital contrast-detail (d-CD) phantom. A structure of the d-CD phantom was determined on the basis of the actual images of GGOs and background noises of 22 patients who were diagnosed as GGO by chest HRCT. The d-CD phantom has a 512×512 matrix in size and has total of 100 holes: the diameter of these holes increases stepwise from 2 to 20 pixels with 2 pixels interval in a vertical direction and the CT value varies stepwise from 2 to 200 HU in a horizontal direction. The observer performance study was carried out for three different display sizes (30 cm×30 cm as an enlarged size, 13 cm×13 cm as an original size, and 7 cm×7 cm as a reduced size) using a 2-megapixels LCD monitor, and it was analyzed using Friedman and Wilcoxon statistical tests. As a result, the observer performance for the original display and the reduced display sizes was superior to that for the enlarged size (P=0.006 and 0.037 for the original display and the reduced display sizes, respectively), whereas there was no significant difference between the original display and reduced display sizes (P=0.77). The d-CD phantom enables a short-term evaluation of observer performance and is useful in analyzing relationship between display size and observer performance.

Patient setup verification procedure for a portal image in a computed radiography system with a high-resolution liquid-crystal display monitor.

In our conventional visual inspection for setup verification, we have routinely used a console monitor of a CR system and a monitor of a treatment-planning system (i.e., the separate-monitor method) in order to avoid the need for CR portal-film generation. However, the separate-monitor method provided insufficient precision in detecting setup errors. We devised a setup verification procedure that uses a high-resolution liquid-crystal display monitor (i.e., the single-monitor method). Our objective in the present study was to evaluate the precision of the single-monitor method. These two methods were compared in terms of the precision of visual inspection. The single-monitor method was significantly superior to the separate-monitor method in sensitivity and in the magnitude of the discrepancy that could not be detected. The single-monitor method provides higher precision in visual inspection than does the separate-monitor method, and is a useful verification procedure.

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

RATIONALE AND OBJECTIVES: 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. MATERIALS AND METHODS: 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). RESULTS: 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). CONCLUSION: 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.