Rationale and Objectives
The purpose of this study was to evaluate the diagnostic accuracy of radiologists using monochrome medical-grade 5 megapixel (MP), 3 MP, 2 MP, and 1 MP displays for the detection of cervical fractures on cervical radiographs, while controlling factors such as luminance and ambient conditions.
Materials and Methods
Institutional review board approval was obtained. Two hundred lateral cervical computed radiography images, 97 with fractures, were randomly displayed on 5-MP, 3-MP, 2-MP, or 1-MP liquid crystal displays (LCDs) for a total of 450 interpretations per display. These radiographs were presented in eight sessions, each with 25 radiographs, to nine readers. The reference standard for all cases was computed tomography. Ambient lighting, monitor luminance, and gamma were controlled throughout the study. Measures included receiver operator characteristic areas under the curve (AUC), sensitivity, specificity, and accuracy, mean elapsed time by display, and mean confidence level by display. One way analysis of variance was performed. Results were considered to be significant at an alpha level of 0.05.
Results
AUCs were 0.76 (95% CI, 0.72–0.80) for the 1 MP, 0.80 (95% CI, 0.76–0.84) for the 2 MP, 0.77 (95% CI, 0.73–0.81) for the 3 MP, and 0.76 (95% CI, 0.72–0.80) for the 5 MP medical grade LCDs. There was no significant difference in the AUCs ( P values between .0651 and .8693), confidence ( P = .158), or interpretation times ( P = .751).
Conclusion
When controlling factors such as luminance and ambient light, a difference in accuracy in the detection of cervical fractures by resolution could not be detected when using medical-grade displays. Interpretation time and confidence were also not affected by resolution.
The use of lower resolution medical grade monochrome displays is becoming more common in medical imaging. These displays may have some of the same features as higher resolution displays, with comparable luminance, contrast ratios, and methods for calibration, but are more cost effective. As these liquid crystal displays (LCDs) have become increasingly popular for general radiology practices in a digital environment, the 5 megapixel (MP) cathode ray tubes (CRTs) used by the early adopters of Picture Archiving and Communication Systems (PACS) have been replaced in most settings by LCDs which are nominally of 3 MP or, less commonly, even lower resolution. This has lead to heterogeneous display environments in clinical settings.
With the exception of digital mammography , regulatory mandates for minimum resolution requirements of medical display systems do not exist today in the United States. However, the American College of Radiology Technical Standard for the Electronic Practice of Medical Imaging provides specific illustrations of whether monitors would require the use of magnification to achieve the recommended displayed resolution of 2.5 line pairs (lp)/millimeter (mm). It states that a “5 MP (2048 × 2560) monitor exceeds the American College of Radiology standard of a displayed resolution of at least 2.5 lp/mm when viewing a 14“ × 17” image and thus is sufficient for viewing all types of computed radiography/digital radiography images, a “2 MP (1200 × 1600) or 3 MP (1535 × 2048) monitor needs a 2× magnification when viewing 14“ x 17” images,” and “a 1K × 1.2K (1024 × 1280) will not permit a 10“ × 12”, 12“ × 14”, or a 14“ × 17” image with at least 2.5 lp/mm resolution without zooming or magnifying the image” .
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Materials and methods
Subjects and Reference Standards
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Descriptive Statistics of Cases
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Acquisition
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Reading Sessions
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Displays
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Training Session
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Reading Sessions
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Ambient Conditions
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Statistics
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Results
Sensitivity, Specificity, and Accuracy for Detection of the Presence of Fractures for Each Monitor
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Table 1
Accuracy, Sensitivity, and Specificity for Detecting Cervical Fracture with Different Monitor Resolutions
1 mp 2 mp 3 mp 5 mp Accuracy: 77% Accuracy: 80% Accuracy: 78% Accuracy: 76% Sensitivity: 70% Sensitivity: 73% Sensitivity: 69% Sensitivity: 74% Specificity: 84% Specificity: 87% Specificity: 86% Specificity: 79%
mp, megapixel.
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ROC Curves for Detection of the Presence of Fractures at the Case Level for Each Monitor
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Table 2
Statistical Analysis of ROC Curves for the Various Monitor Resolutions
Display Area Under Curve 95% CI 1 mp 0.76 0.72–0.80 2 mp 0.80 0.76–0.84 3 mp 0.77 0.73–0.81 5 mp 0.76 0.72–0.80
Contrast Difference 95% CI_P_ 1mp vs 2 mp −0.04 −0.08 to 0.00 .0714 1 mp vs 3 mp −0.01 −0.05 to 0.03 .5562 1 mp vs 5 mp 0.00 −0.04 to 0.04 .8693 2 mp vs 3 mp 0.03 −0.01 to 0.06 .1757 2 mp vs 5 mp 0.03 0.00 to 0.07 .0651 3 mp vs 5 mp 0.01 −0.03 to 0.05 .6384
CI, confidence interval; mp, megapixel; ROC, receiver operator characteristic.
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Sensitivity and Specificity for Detection of the Presence of Fractures for Each Reader
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Table 3
Sensitivity and Specificity for Detection of Cervical Fracture for all Nine Readers
Sensitivity 95% CI Specificity 95% CI Reader 1 0.695 0.592–0.785 0.895 0.820–0.947 Reader 2 0.621 0.516–0.719 0.886 0.809–0.940 Reader 3 0.695 0.592–0.785 0.886 0.809–0.940 Reader 4 0.779 0.682–0.858 0.800 0.711–0.872 Reader 5 0.737 0.636–0.822 0.829 0.743–0.895 Reader 6 0.684 0.581–0.776 0.838 0.753–0.903 Reader 7 0.779 0.682–0.858 0.790 0.700–0.864 Reader 8 0.684 0.581–0.776 0.790 0.700–0.864 Reader 9 0.758 0.659–0.840 0.810 0.721–0.880
CI, confidence interval.
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Time Difference between Monitors
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Confidence Differences by Monitor
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Discussion
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