Rationale and Objectives
To evaluate the comparative performance of high-fidelity liquid crystal display (LCD) and cathode ray tube (CRT) devices for mammography applications, and to assess the impact of LCD viewing angle on detection accuracy.
Materials and Methods
Ninety 1 k × 1 k images were selected from a database of digital mammograms: 30 without any abnormality present, 30 with subtle masses, and 30 with subtle microcalcifications. The images were used with waived informed consent, Health Insurance Portability and Accountability Act compliance, and Institutional Review Board approval. With postprocessing presentation identical to those of the commercial mammography system used, 1 k × 1 k sections of images were viewed on a monochrome CRT and a color LCD in native grayscale, and with a grayscale representative of images viewed from a 30° or 50° off-normal viewing angle. Randomized images were independently scored by four experienced breast radiologists for the presence of lesions using a 0–100 grading scale. To compare diagnostic performance of the display modes, observer scores were analyzed using receiver operating characteristic (ROC) and analysis of variance.
Results
For masses and microcalcifications, the detection rate in terms of the area under the ROC curve (A z ) showed a 2% increase and a 4% decrease from CRT to LCD, respectively. However, differences were not statistically significant ( P > .05). The viewing angle data showed better microcalcification detection but lower mass detection at 30° viewing orientation. The overall results varied notably from observer to observer yielding no statistically discernible trends across all observers, suggesting that within the 0–50° viewing angle range and in a controlled observer experiment, the variation in the contrast response of the LCD has little or no impact on the detection of mammographic lesions.
Conclusions
Although CRTs and LCDs differ in terms of angular response, resolution, noise, and color, these characteristics seem to have little influence on the detection of mammographic lesions. The results suggest comparable performance in clinical applications of the two devices.
The image technology for screening mammography is in a transition, with conventional analog screen-film mammography systems being gradually replaced by digital mammography systems. The transition is expected to accelerate because of a recent large-scale trial that found an essential equivalence of the two modalities for the majority of women but a notable advantage of digital for women with dense breasts ( ).
Soft-copy display is an integral element of digital mammography without which many advantages of digital mammography such as efficiency and optimized image quality would not be fully realized. Soft-copy display of digital mammograms may be achieved via two types of display devices: liquid crystal display (LCD) and cathode ray tube (CRT). These displays present distinctly differing resolution and noise characteristics. LCDs offer higher resolution but poorer noise performance than CRTs ( ). LCD technology has also enabled incorporation of color without an undue effect on display contrast, a common problem with color CRT displays, color CRTS have notably lower contrast ratios than their monochrome counterpart. This improvement suggests the possibility of using color LCDs for diagnosis. However, LCDs exhibit a non-Lambertian angular response characteristic by which the luminance and contrast of the displayed image changes as a function of viewing angle. Display specifications often characterize the angular response in terms of angular cones within which the luminance ratio exceeds 10, a threshold applicable to text applications. Using this metric, angular response specifications of 160–170° are common. However, within those ranges, the contrast of the medical images can change significantly, potentially affecting the diagnostic utility of LCDs.
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Materials and methods
Images
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Display Systems
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Observer Experiment
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Statistical Analysis
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Results
Detection of Microcalcifications
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Table 1
Values for the Areas Under the ROC Curve (A z ) Associated With the Detection of Microcalcifications and Masses for Each Display (CRT and LCD at Different Viewing Angles) and for Each of the Four Observers
Observer CRT_0 LCD_0 LCD_30 LCD_50 Microcalcification Detection A 0.84 ± 0.05 0.83 ± 0.05 0.88 ± 0.04 0.87 ± 0.05 B 0.90 ± 0.05 0.87 ± 0.06 0.89 ± 0.05 0.88 ± 0.05 C 0.91 ± 0.04 0.82 ± 0.06 0.92 ± 0.03 0.84 ± 0.05 D 0.89 ± 0.04 0.87 ± 0.04 0.89 ± 0.04 0.87 ± 0.05 All 0.89 ± 0.04 0.85 ± 0.05 0.90 ± 0.04 0.86 ± 0.05 Mass Detection A 0.76 ± 0.07 0.83 ± 0.05 0.79 ± 0.06 0.81 ± 0.06 B 0.85 ± 0.07 0.82 ± 0.06 0.85 ± 0.06 0.88 ± 0.05 C 0.89 ± 0.04 0.84 ± 0.05 0.83 ± 0.05 0.83 ± 0.05 D 0.80 ± 0.06 0.85 ± 0.05 0.76 ± 0.06 0.81 ± 0.06 All 0.82 ± 0.06 0.84 ± 0.05 0.81 ± 0.06 0.83 ± 0.05
Note.—ROC, receiver operating characteristics; CRT, cathode ray tube; LCD, liquid crystal display.
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Table 2
The Results of the Analysis of Variance Indicating that only the Case Variability Exhibited a Statistically Significant Impact
Source of Variability Microcalcification Detection P Value Mass Detection P Value Display .1316 .5284 Case <.05 ⁎ <.05 ⁎ Reader .5517 .5094 Display-Case .0766 .8405 Display-Reader .8975 .5875 Reader-Case <.05 ⁎
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Detection of Masses
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Discussion
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Conclusions
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