Noriyuki Hashimoto

Effect of test patterns on measurement of the luminance of LCD devices by use of a telescopic-type luminance meter

Quality assurance of electronic display devices is important for maintaining reliable soft-copy image interpretations. This paper presents effects of test patterns on measurement of the luminance of liquid-crystal display (LCD) devices by use of a telescopic-type luminance meter. The luminance for different types of test patterns having different backgrounds and measurement areas was measured and compared with the results obtained with AAPM task group-18 (TG-18) LN test patterns. The luminance measured for the test patterns with a black background was lower than that measured for TG-18 LN test patterns due to the light emitted from the outside the focused area of the telescopic-type luminance meter. Also, the luminance obtained with smaller measurement areas indicated lower luminance. These tendencies were particularly obvious at low luminance. The luminance of the LCD device by use of a telescopic-type luminance meter should be measured with test patterns that have a black background and a smaller measurement area than that for the TG-18 LN test patterns.

A preliminary study for exploring the luminance ratio of liquid-crystal displays required for display of radiographs

Medical-grade liquid-crystal displays (LCDs) with high contrast ratio (CR) values have recently been developed and become available for soft-copy reading. When the LCD is used under ambient light conditions, the luminance ratio (LR) is a more appropriate indicator than the CR. Our aim was to explore the LR required for LCDs for soft-copy reading by comparing the effective LR values with the LR of the LCD. We defined “the luminance ratio in an image (LRimg)”, the ratio of the maximum to minimum luminance in a radiograph displayed on the LCD, as the effective LR values required for the LCD. The maximum LRimg values in chest radiographs and those in mammograms ranged from 109 to 143 and 372 to 431, respectively. The LR of the LCD was higher than the LRimg values of the radiographs. Our results indicate that currently available medical-grade LCDs have enough LR for display of radiographs.

Effect of fluorescent lighting on the color of liquid-crystal displays

Liquid-crystal displays (LCDs) are used for displaying medical images under various illuminance conditions and with ambient-lighting colors. Our purpose in this study was to understand the variations of the chromaticity in LCDs under different fluorescent lighting conditions. The variation of chromaticity of LCDs at a white point consisting of equivalent pixel value in Red, Green, and Blue was examined under different types of fluorescent lighting. The direction of changes in the chromaticity diagram shifted to the color of each fluorescent lighting. When the differences in chromaticity (∆u′v′) increased, the observers’ confidence levels in distinguishing color differences also increased. When the luminance of the LCD increased, observers’ sensitivities for recognizing differences in chromaticity also increased as compared to observers’ sensitivities at lower luminances. Our results indicate that observers recognized slightly yellowish colors even if ∆u′v′ was less than 0.01; thus, observers could perceive differences in chromaticity. These results could provide important and relevant information with regard to better ambient lighting conditions in an image-reading room.

Effect of ambient lighting on liquid–crystal displays with different types of surface treatment

Liquid–crystal displays (LCDs) with different types of surface treatment have been developed for decreasing the effect of ambient lighting on a displayed image. The effect of ambient lighting on LCDs with different surface treatments, namely, glare (G)-type, anti-glare (AG)-type, and anti-reflection (AR)-coating LCDs, was evaluated quantitatively in this study for appropriate selection. The effect of ambient lighting on diffuse reflection and specular reflection was investigated. The coefficient of diffuse reflection of the AR-coating LCD was smaller than the others. The effect of diffuse reflection on the display function of each LCD was evaluated in terms of the deviation of the contrast response at the lowest luminance level when the illuminance changed from the condition that was used for calibration of the grayscale standard display function. The display function of the AR-coating LCD was affected less by diffuse reflection compared to the others. On the other hand, the coefficient of specular reflection of the AG-type LCD was the smallest until the angle of aperture of the light source was 4.6°. The specular-reflected image on the AG-type LCD had a remarkably broad distribution compared to the others. Our results are merely examples for a limited number of LCDs; however, we clarified quantitatively that the AR-coating and the AG-type LCDs were affected less by diffuse and specular reflection than the G-type LCD.

Effect of angular performance on the chromaticity of grayscale images displayed on medical liquid-crystal displays

Although variation of chromaticity in medical liquid-crystal displays (LCDs) has created interest in the quality assurance and quality control of display devices for medical use, it is unknown how chromaticity varies with the viewing angle. Our aims in this study were to investigate the variations of chromaticity in grayscale images displayed on medical LCDs depending on viewing angles, and to examine color discrimination at different viewing angles. Variations in chromaticity, Δu′v′, between 0° and each viewing angle (−60° to +60°) were investigated. The chromaticity of each LCD varied as the viewing angle changed. We examined confidence levels of color discrimination at different viewing angles by rotating the LCD for ten observers. When the viewing angle and variation in chromaticity increased, the confidence levels of color discrimination increased. Our results indicated that observers, such as radiologists and radiological technologists, could recognize variation in chromaticity at different viewing angles.

Visual assessment method of angular performance in medical liquid-crystal displays by use of the ANG test pattern: Effect of ambient illuminance and effectiveness of modified scoring

A visual assessment method of the angular performance in medical liquid–crystal displays (LCDs) by use of the “ANG test pattern” was proposed by Badano and the International Electrotechnical Commission. Our goals were to examine the effect of ambient illuminance on the visual assessment, and to investigate whether our modified visual assessment (with the ANG test pattern) can be used instead of the conventional assessment based on luminance measurements. As the ambient illuminance increased, the original scores obtained with the visual assessment decreased. The modified score of the visual assessment was in reasonable agreement with the results of the luminance-based assessment. We conclude that the visual assessment with the ANG test pattern should be performed in a room with constant ambient illuminance, and the modified visual assessment could have the potential to be used instead of the luminance-based assessment for quality assurance of medical LCDs.

SU‐E‐I‐16: Comparison of the Blue Part of the Spectral Power Distribution in a Medical Liquid‐Crystal Display for Different Color Temperature Settings

PURPOSE The effects of blue light exposure on visual fatigue have received much attention in recent years. There have been attempts to reduce the blue part of the spectral power distribution in a displays output by using commercial films and glasses. However, reducing the blue part of the spectral power distribution in medical liquid-crystal displays (LCDs) by changing the color temperature settings may prove to be a simpler solution. Our study aimed to quantitatively compare the blue part of the spectral power distribution of a medical LCD in different color temperature settings. MATERIALS AND METHODS We used two color LCDs (RadiForce RX340, 400 cd/m2 , EIZO). The spectral power distribution, chromaticity, and correlated color temperature were measured for LCDs with different color temperature settings (6500, 7500, and 8500 K). The default color temperature setting of the medical LCDs used in this study was 7500 K. A spectroradiometer (CS-2000, KONICA MINOLTA) and original gray-scale test patterns with 18 different luminance levels were used for the measurements. RESULTS The blue parts of the spectral power distribution (380-495 nm) were different for each color temperature setting. The integrated power values over the blue of the spectral power distribution decreased by 9% from 8500 to 7500 K and 13% and from 7500 to 6500 K. The correlated color temperature changed by approximately 1000 K depending on the color temperature setting. The difference in the chromaticity was 0.011 between 8500 and 7500 K and between 7500 and 6500 K. CONCLUSION Our results quantitatively indicate that the blue part of the spectral power distribution of the medical LCDs tested varies for different settings of color temperature.

SU‐E‐I‐44: Investigation of the Contrast Ratio Required for Medical‐Grade Liquid‐Crystal Displays

Purpose: Liquid‐crystal displays (LCDs) with a higher contrast ratio (CR) have been recently developed. However, only a few studies have been reported regarding the CR of the LCDs required for displaying medical images. The purpose of this study was to investigate the CR of LCDs required for displaying medicalimages.Methods: A two‐megapixel monochrome LCD (GS220, maximum 1,000 cd/m2, recommended 500 cd/m2, Eizo Nanao, Japan) was used in this study. This LCD was calibrated to the grayscale standard display function (GSDF) with different maximum‐luminance settings such as 250, 500, and 700 cd/m2 for mammograms and 175, 500, and 700 cd/m2 for chest radiographs. The minimum luminance of the LCD was kept at 0.7 cd/m2 for each calibration. The CR was calculated from the maximum and minimum luminance of each luminance setting. Mammograms (40 images) and chest radiographs (10 images) were selected as research subjects. To examine the maximum luminance (Lmax) and the minimum luminance (Lmin) in each image, region of interests (ROIs) were set based on the histogram analysis. Then, luminance corresponding to ROIs was calculated by using the GSDF curve with different maximum luminance settings. Finally, luminance ratio (LRimg) in mammograms and chest radiographs were obtained from the Lmax and Lmin in each image.Results: The average LRimg of mammograms with the maximum‐luminance setting of 250, 500, and 700 cd/m2 was 209:1, 388:1, and 523:1, respectively. On the other hand, the average LRimg of chest radiographs with the maximum‐luminance settings of 175, 500, and 700 cd/m2 was 37:1, 70:1, and 86:1, respectively Conclusions: We found that the CR of the LCD required for displaying mammograms and chest radiographs ranged from 209:1 to 523:1 and 37:1 to 86:1, respectively. A significant difference in the CR of LCD required for displaying medical image was observed between mammograms and chest radiographs.

SU‐E‐I‐43: Verification of the Usefulness of Evaluation Method for Angular Performance with the ANG Test Pattern

Purpose: A simple method with the ANG test pattern to evaluate the angular performance of medical‐grade liquid‐crystal display (LCD) monitors was proposed by the International Electrotechnical Commission (IEC) in December 2009 (IEC 62563‐1). The purpose of this study was to investigate correlation between the results obtained by using the ANG test pattern and the angular performance measured by a luminance meter. We also examined the effect of ambient‐light conditions on the results evaluated by using the ANG test pattern. Methods: Three LCDs, a medical‐grade monochrome LCD (Radiforce GS220, 500 cd/m2, Eizo Nanao), a medical‐grade color LCD (Radiforce RX211, 300 cd/m2, Eizo Nanao), and a general‐purpose LCD (SyncMaster940B, 180 cd/m2, Samsung) were used in this study. The ANG test pattern was observed by eight observers under three ambient‐light conditions (0, 35, and 327 lux). Two different scoring methods were used. One is the method proposed by the IEC 62563‐1, and the other is the method modified for comparison of results measured by a luminance meter. The luminance performance was measured as a function of viewing angle, and evaluated as the relative contrast ratio. Finally, the results in terms of the modified scores were compared to the luminance performance in various viewing angles. Results: Variations of the modified scores and the relative contrast ratio as a function of viewing angle indicated a similar tendency for medical‐grade LCDs. On the other hand, the two results did not correspond well for the general‐purpose LCD. The difference between the results obtained at 0 and 327 lux was 0.11 at a maximum for all LCDs used in this study. Conclusions: The evaluation method with the ANG test pattern is considered to be useful for evaluation of the angular performance for medical‐grade LCDs taking ambient‐light conditions into consideration.

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.