Keita Takahashi

Magnetic Phase Diagram of a Random Mixture with Competing Interactions: Co1-xMnxCl2·2H2O

Magnetic and thermal properties of Co 1- x Mn x Cl 2 ·2H 2 O with competing exchange interactions have been studied experimentally, For the system with x ∼0.5, the magnetic heat capacity have revealed only a broad maximum around 5 K, which is quite different from the heat capacity peak of λ-type for the pure systems and similar to that observed in metallic spin-glasses. The hysteresis in the magnetic susceptibility and thermoremanent magnetization have been observed in the mixtures with x ≤0.5, reflecting the frustration of magnetic interactions, while normal antiferromagnetic behavior has been seen in the region x >0.5. The magnetic phase diagram of this system is given, which contains four states: paramagnetic, antiferromagnetic, frustrated antiferromagnetic and anisotropic spin-glass states.

SU‐GG‐I‐49: Comparison of the Visual Fatigue with a High‐Brightness Color LCD and a Monochrome LCD

Purpose: To investigate whether there are the differences among the visual fatigue of observers in the 500 cd/m2 color and the monochrome LCDs and the 170 cd/m2 color LCD (two‐mega pixels). Method and Materials: Posteroanterior chest radiographs with a lung nodule were displayed on a high‐brightness color LCD (Radiforce RX211, Eizo) with two maximum luminance settings (500 and 170 cd/m2) and a monochrome LCD (500 cd/m2, Radiforce GS220, Eizo). Six radiologic technologists aged 24.0±1.3 years were independently trained to understand various lung nodules for two hours, deemed the “Fatigue Session”. The visual fatigue of observers was evaluated in terms of the critical flicker fusion frequency (CFFF) and the visual accommodation time by use of a flicker device (Handy Flicker HF, Neitz) and an accommodation device (HS‐9E, Kowa), respectively. The measurement of the degree of visual fatigue was performed before and after the Fatigue Session for each observer. Both the decrement of the CFFF and the extension of the accommodation time were utilized as a measure of visual fatigue. The ambient lighting was set at 35 lux during all Fatigue Sessions and the measurement of visual fatigue. Results: The average visual fatigue that analyzed both the CFFF and accommodation time increased after the Fatigue Sessions. The CFFF with the 500 cd/m2 color, monochrome LCDs, and the 170 cd/m2 color LCD decreased 3.7, 3.9, and 5.6%, respectively. The accommodation times after the Fatigue Sessions with the 500 cd/m2 color, monochrome LCDs, and the 170 cd/m2 color LCD were extended by 18.5, 18.1, and 3.2%, respectively. Conclusion: In terms of the decrement of the CFFF, there were little differences among the three monitor conditions. On the other hand, the extension of the accommodation time with the 500 cd/m2 color and monochrome LCD was longer than that of the 170 cd/m2 color LCD.

SU‐GG‐I‐48: Evaluation of Viewing Angle Performance on the Latest High‐Brightness Color LCD Monitors with the In‐Plane Switching Panel for Medical Images

Purpose: Our purpose was to compare the viewing angle performance on high‐brightness color liquid‐crystal display (LCD) monitors to that of monochrome LCD monitors. Method and Materials: We used four LCD monitors with an in‐plane switching (IPS) panel: two high‐brightness color LCD unt il 300 cd/m2, two‐megapixel, Eizo), and RX210, 220, cd/m2, two‐megapixel, Eizo), and two monochrome LCD monitors, (GS220, 500 cd/m2, two‐megapixel, Eizo, and G31‐S, 450 cd/m2, three‐megapixel, Eizo). The luminance performance of each LCD monitor was measured as a function of the viewing angle (−60° to +60°) in the horizontal, the vertical, and the diagonal directions by use of a telescopic‐type luminance meter without any ambient lighting. The viewing angle performance was evaluated with a relative contrast ratio of 70 % or greater. Results: The range of viewing angle in terms of relative contrast ratio on the 300 cd/m2 high‐brightness color, the 240 cd/m2 high‐brightness color, the 500 cd/m2 two‐megapixel monochrome, and the 450 cd/m2 three‐megapixel monochrome LCD monitors with similar IPS panels were 34° to 74°, 29° to 48°, 55° to 81°, and 39° to 74°, respectively. The relative contrast ratios showed notable variations for different viewing angles in spite of similar types of panels. Our results indicate that the viewing angle performance on the 240 cd/m2 color LCD monitor tended to provide a slightly inferior angular performance to the two monochrome LCD monitors used in this study. On the other hand, the 300 cd/m2 color LCD monitor had a comparable viewing angle performance with the 450 cd/m2 monochrome LCD monitor. Conclusion: The viewing angle performance on the high‐brightness color LCD monitors is inferior to that of monochrome LCD monitors. However the 300 cd/m2 color LCD monitor had comparable viewing angle performance with the 450 cd/m2 monochrome LCD monitor.

SU-GG-I-50: When Should We Recalibrate the Grayscale Standard Display Function in Different Ambient Lighting Conditions?

Purpose: Liquid‐crystal display (LCD) monitors for medical use may not be always used under the same ambient lighting condition for calibration of the grayscale standard display function (GSDF). The purpose of this study is to clarify need for recalibration to the GSDF in different ambient lighting conditions. Method and Materials: An LCD monitor (two‐mega pixels, Radiforce GS220, Eizo, Japan) was used in this study. The calculated diffuse reflection coefficient of this LCD monitor was 0.0026 sr−1. This LCD monitor was calibrated to the GSDF including four ambient lighting conditions such as typical diagnostic reading stations (10 lx and 60 lx), hospital clinical viewing stations (250 lx), and operating rooms (400 lx) levels based on guidelines of the American Association of Physicists in Medicine task group (AAPM TG) 18. The maximum deviation from the contrast response was calculated at various tentative changes in ambient lighting conditions. Results: When the ambient lighting condition changed, the maximum deviation of contrast responses increased. The degree of the effect of the change of ambient lighting depended on the ambient lighting conditions used for the calibration to the GSDF. The darker the ambient lighting condition for calibration was, the greater the variation in the contrast response was. If 50 lx and 100 lx were added to typical diagnostic reading stations (10 lx), the maximum deviations of the contrast response were −10.3% and −18.5%, respectively. Those maximum deviations of the contrast response were beyond an acceptable range (±10%) of AAPM TG18. Thus, the contrast in especially dark regions of medical images will be decreased. Conclusion: As the LCD monitor calibrated included typical diagnostic reading stations (10 lx), the need for recalibration to the GSDF with ambient lighting conditions increased over 50 lx to maintain imagecontrast.

MO‐FF‐A4‐05: Comparison of Detectability of a Simple Object with Low Contrast Displayed On a High‐Brightness Color LCD Monitor and a Monochrome LCD Monitor

Purpose: To examine the potential usefulness of a high‐brightness color liquid crystal display(LCD) monitor, the detectability of the color monitor was compared with the detectability of a monochrome LCD monitor by using receiver operating characteristic (ROC) analysis.Materials and Method: Two LCD monitors were used in this study: a two‐megapixel high‐brightness color monitor (RX‐211, 750 cd/m2 (maximum), Nanao, Japan), and a two‐megapixel monochrome monitor (GS‐220, 1,000 cd/m2 (maximum), Nanao, Japan). Both monitors were calibrated to grayscale standard display function. We examined the detectability of a color LCD monitor with different luminance settings (500 and 170 cd/m2) and a monochrome LCD monitor (500 cd/m2). Totally, 40 images were taken — including 20 images with a ball (8 mm in diameter), which was used as a signal and put on the surface of a 15.5 cm acrylic plate. All images were acquired by use of a computed radiographic system (CR9000, Fuji Film, Japan). All images were displayed on the LCD monitors with 8‐bit gray scale without any ambient lighting. Finally, the confidence data obtained by thirteen observers were analyzed by use of software (DBM MRMC, The University of Chicago) for ROC analysis, and the statistically significant differences between the areas under the ROC curve (AUC) were determined with the jackknife method. Results: The AUCs of color the LCD monitor with a maximum luminance of 500 cd/m2, 170 cd/m2 and monochrome LCD monitor with a maximum luminance of 500 cd/m2 were 0.937, 0.924, and 0.915, respectively. There were no statistically significant differences between the monochrome LCD monitor and the color LCD monitor with different luminance settings. Conclusion: The detectability of a high‐brightness color LCD monitor indicated comparable performances obtained with a monochrome LCD monitor.