Medical Liquid Crystal Display Research Articles

Medical display application for degraded image sharpness restoration based on the modulation transfer function: initial assessment for a five-megapixel mammography display monitor.

An image-display application for medical liquid-crystal display (LCD) monitors called the sharpness recovery (SR) function has been developed to compensate for image sharpness as a function of deficiencies in the modulation transfer function (MTF) of a monitor. We investigated the effects of the SR function for a five-megapixel (MP) mammography LCD monitor on the resolution and noise properties of the displayed images by measuring the MTF and overall noise power spectrum (NPS), respectively. Furthermore, the effectiveness of the SR function for the 5-MP monitor in displaying subtle microcalcifications on digital mammograms was verified using a two-alternative-forced-choice sensitivity measurement as an initial application for medical image interpretation. Four radiologists compared the visibility of 45 regions of interest with a malignant microcalcification cluster shown on SR-processed and unprocessed mammograms. SR processing improved the MTF of the displayed images by approximately 40% at the Nyquist frequency of the 5-MP monitor, whereas it slightly increased the overall NPS values. All observers indicated that the fraction of cases considered to have better visibility of microcalcifications with the SR processing was significantly greater than that without the processing (averaging 82%, with the 95% confidence interval ranging from 70 to 93%). The SR processing for the 5-MP monitor yielded a significant improvement in the resolution properties of the displayed images, with a certain increase in the image noise. The SR function has the potential to improve the observer performance of radiologists, particularly when reading subtle microcalcifications reproduced on 5-MP monitors.

Examination of the Maximum Brightness of the Monitor Suitable for Radiological Technologists' Interpretation Assistance and Image Inspection

The purpose of this study is to examine the maximum brightness of the monitor, which is suitable for radiological technologists' (hereinafter referred to as technicians) interpretation assistance and image inspection. The signal detection ability was evaluated by receiver operating characteristic (ROC) analysis using a chest X-ray image with a simulated nodule. In order to examine the ease of observation and the effect on the subjective evaluation by changing the maximum brightness, evaluation was performed by the normalized ranking method using chest X-ray images. ROC experiments were performed using images with and without simulated nodules in the chest phantom. There was no significant difference in detectability by changing the maximum brightness (p>0.05), but the average area under the curve (AUC) was higher at 350 cd/m2 than at 100 cd/m2 and 170 cd/m2. A normalized ranking method was performed focusing on simulated nodules on chest X-ray images. In the least significant difference (l.s.d.) method, there was a significant difference between the maximum luminance, and the higher the maximum luminance, the better the evaluation. From these results, the change in the maximum brightness did not significantly affect the signal detection ability of the technician's chest X-ray image, but the higher the maximum brightness, the easier it was to observe and the higher the subjective evaluation. It has been reported that the higher the maximum brightness, the shorter the signal recognition time, and a monitor with a high maximum brightness may lead to more efficient image inspection by a technician. From the results of this study, it is considered appropriate to use a medical liquid crystal display (LCD) monitor with a maximum brightness of 350 cd/m2 for the technician's interpretation assistance and image inspection.

Assessment Tool of Image Quality for Medical Liquid-crystal Displays Using Commercially Available Digital Cameras

We developed a simplified tool for measuring image quality of medical liquid-crystal displays (LCDs) using a commercially available color digital camera. This tool implemented as a plug-in software for ImageJ (open-source image processing program) was designed to compute modulation transfer functions (MTFs) and Wiener spectra (WS) of monochrome and color LCDs from LCD photographed images captured by a camera. The intensities of the red (R), green (G), and blue (B) signals of the unprocessed image data depend on the spectral sensitivity of the image sensor used in the camera. In order to evaluate image quality based on LCD luminance, the plug-in software calibrates the RGB signals from the camera using measured luminance of the LCD and converts them into grayscale signals that correspond to the luminance of the LCD. The MTFs and WS are determined based on the line response from a one-pixel line image and the one-dimensional noise profiles acquired by scanning the uniform image using numerically synthesized slit, respectively. With this plug-in software for ImageJ, we are able to readily compute MTFs and WS of both monochrome and color LCDs from unprocessed image data of cameras. Our simplified tool is helpful to evaluate and understand the physical performance of LCDs for a large number of display users in hospitals and medical centers.

Effect of Color Temperature on Color Scale Test Patterns in Medical Liquid-crystal Display Monitor

In Japan, medical liquid-crystal display (LCD) and general LCD monitors have color temperatures of 7500 and 6500 K, respectively. The differences in color temperature make it difficult for radiologists to judge whether the same color is being displayed on the monitor. Therefore, the radiologist may overlook lesions. We examined chromaticity on a color scale test pattern to determine the relationships between color temperature (6500-12,500 K) of the medical color LCD monitors, there are three types of fluorescent light and three types of illuminance LCD monitors. As the color temperature of the monitor increased, the variation in chromaticity for grayscale test patterns increased and those variations for the blue scale test patterns decreased in a dark room and at 600 lux. In addition, even if the color temperature of the monitor was changed, the variation in chromaticity showed no change under fluorescent lighting with light bulb color and daylight color. The results of this study will be useful for quality control and quality assurance of medical LCD monitors in terms of illuminance and color temperature of the monitor.

Effective luminance deterioration of medical liquid crystal displays in clinical use.

The objective of this work was to evaluate the maximum luminance (L max) level of medical liquid crystal displays (LCDs) as a function of backlight hours (BLH) annually. The L max values for 249 2-megapixel color LCDs (RadiForce RX210, EIZO Corporation) were measured in February 2014, 2015, and 2016. Four near-range luminance meters and the built-in type luminance meters, each with an LCD, were used for the measurements. The average and standard deviation (SD) of BLH measured in 2014 was 15,371±8219h. Four, twenty, and thirty-nine LCDs failed in the constancy tests performed in February 2014, 2015, and 2016, respectively, i.e., they were unable to output 170cd/m2. The SD of L max increased each year and as BLH became longer. In conclusion, evaluation of L max as a function of BLH during constancy testing will help predict the decrease in L max of a clinically used medical color LCD.

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 display's 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.

医用液晶ディスプレイと汎用液晶ディスプレイにおける視覚的評価─胸部CT 画像とモノクロ，カラー表示における核医学画像の模擬信号の検出能─

The purpose of this study was to evaluate the detection performance of simulated nodules in chest computed tomography (CT) images and nuclear medicine images with an ordinary liquid crystal display (LCD) and a medical LCD (grayscale standard display function: GSDF) and gamma 2.2. We collected 72 chest CT image slices obtained from an LSCT phantom with simulated signals composed of various sizes and CT values and 78 slices of monochrome and color nuclear medicine images obtained from a digital phantom with a simulated signal composed of various sizes and radiation levels. Six observers performed receiver operating characteristic (ROC) analysis using a continuous scale. The area under the ROC curve (AUC) was calculated for each monitor. The average AUC values for detection of chest CT images on a medical LCD (GSDF), medical LCD (gamma 2.2), and ordinary LCD were 0.71, 0.67, and 0.73, respectively. The average AUC values for detection of monochrome nuclear medicine images using a medical LCD (GSDF), medical LCD (gamma 2.2), and ordinary LCD were 0.81, 0.75, and 0.72, respectively. The average AUC values for detection of color nuclear medicine images on a medical LCD (GSDF), medical LCD (gamma 2.2), and ordinary LCD were 0.88, 0.86, and 0.90, respectively. Observer performance for detection of simulated nodules in chest CT images and nuclear medicine images was not significantly different between the three LCD monitors. We therefore conclude that an ordinary LCD monitor can be used to detect simulated nodules in chest CT images and nuclear medicine images.

An evaluation of organic light emitting diode monitors for medical applications: Great timing, but luminance artifacts

In contrast to the dominant medical liquid crystal display (LCD) technology, organic light-emitting diode (OLED) monitors control the display luminance via separate light-emitting diodes for each pixel and are therefore supposed to overcome many previously documented temporal artifacts of medical LCDs. We assessed the temporal and luminance characteristics of the only currently available OLED monitor designed for use in the medical treatment field (SONY PVM2551MD) and checked the authors' main findings with another SONY OLED device (PVM2541). Temporal properties of the photometric output were measured with an optical transient recorder. Luminances of the three color primaries and white for all 256 digital driving levels (DDLs) were measured with a spectroradiometer. Between the luminances of neighboring DDLs, just noticeable differences were calculated according to a perceptual model developed for medical displays. Luminances of full screen (FS) stimuli were compared to luminances of smaller stimuli with identical DDLs. All measured luminance transition times were below 300 μs. Luminances were independent of the luminance in the preceding frame. However, for the single color primaries, up to 50.5% of the luminances of neighboring DDLs were not perceptually distinguishable. If two color primaries were active simultaneously, between 36.7% and 55.1% of neighboring luminances for increasing DDLs of the third primary were even decreasing. Moreover, luminance saturation effects were observed when too many pixels were active simultaneously. This effect was strongest for white; a small white patch was close to 400 cd/m(2), but in FS the luminance of white saturated at 162 cd/m(2). Due to different saturation levels, the luminance of FS green and FS yellow could exceed the luminance of FS white for identical DDLs. The OLED temporal characteristics are excellent and superior to those of LCDs. However, the OLEDs revealed severe perceptually relevant artifacts with implications for applicability to medical imaging.

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.

Evaluation of Clinical Usefulness of a Medical Monitor Equipped With an Organic Electroluminescence Panel in Comparison With Liquid Crystal Display Monitors

The medical liquid crystal display (LCD) monitor is a conventionally used imaging device for diagnosis and during endoscopic surgery. Recently, a medical organic electroluminescence panel, the organic light-emitting diode (OLED) monitor, was made available commercially. The advantages of the OLED monitor include good color reproducibility, high contrast, and high video responsiveness. In this nonclinical study, we compared the clinical usefulness and image quality of the OLED monitor and those of the LCD monitor using videos of gynecologic endoscopic surgeries. Monitors were set for blind evaluation. Five evaluators with varying experience in endoscopic surgery evaluated 21 surgery videos played simultaneously on an OLED monitor and two LCD monitors for 2 to 3 minutes twice. Evaluators judged 13 clinical usefulness indices and 11 image quality indices using a 5-point scale (1, very good; 5, very poor) for each video. The mean scores of clinical usefulness indices of the OLED monitor and the LCD monitors 1 and 2 were 2.2 to 2.7, 2.1 to 3.3, and 3.0 to 3.2, respectively. Of seven indices measured, five including motion response, the ability to differentiate organs, recognize lesions, and reproduce actual images, and the general impression of picture quality were statistically superior with use of the OLED monitor compared with the LCD monitor 1, and two including ability to distinguish blood vessels and the ureters were statistically superior with use of the LCD monitor 1 compared with the OLED monitor. The mean scores of image quality indices of the OLED monitor and the LCD monitors 1 and 2 were 1.8 to 3.2, 2.6 to 3.6, and 2.8 to 4.0, respectively. Each index of the OLED monitor was superior to or comparable with those of the LCD monitors. We conclude that the OLED monitor is superior to the LCD monitors insofar as several video presentation characteristics required in gynecologic endoscopic surgery. These findings suggest that the OLED monitor is expected to contribute detailed assessment of organs and the operative field.

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.

Chromaticity and correlated color temperature of the white point in medical liquid–crystal display

The color characteristics of medical liquid-crystal displays (LCDs) have become one of the main interests in quality assurance and quality control of medical display devices. It is necessary to evaluate variations of the color characteristics in medical LCDs in order to provide consistent color characteristics for image reading. In this study, we characterize the color characteristics in grayscale images displayed on medical LCDs. Eight medical color LCDs and eight medical monochrome LCDs were used in this study with operating times ranging from 800 to 25 000 h. Default settings of correlated color temperature (CCT) of white points for all color LCDs were set at 7500 K. We measured chromaticity in the Commission Internationale de l'Éclairage (CIE) u'v' color space and CCT of the white point at 18 luminance levels. A colorimeter and grayscale test patterns with various luminance levels were used for the measurements. First, we examined differences in chromaticity and CCT at 18 luminance levels for each LCD. Second, we compared chromaticities of the different LCDs. Then, chromaticity and CCT of LCDs were measured at different ambient light conditions (30 and 560 lux) and compared to those measured in a dark room. Finally, the relationship between operating times and CCT was evaluated. The chromaticities of monochrome LCDs changed toward the blue and CCT increased as luminance decreased. In color LCDs, the chromaticity and CCT of the white point except at the minimum luminance were nearly constant to those measured at the maximum luminance. We observed differences in chromaticity between color and monochrome LCDs because of the nonadjustable white point of monochrome LCDs. When the ambient light increased, chromaticity varied, and CCT decreased on every LCD. Ambient light had a much greater impact on chromaticity and CCT at lower luminance levels. The CCT of LCDs decreased in longer operating times. The grayscale of LCDs with longer operating times was measured to be more yellowish due to the degradation of cold cathode fluorescent lamps. Our results clearly indicate that the white point in grayscale images displayed on medical LCDs changes depending on luminance levels, color or monochrome LCDs, ambient light conditions, and operating times. These data provide useful information to understand color characteristics of LCD for image reading, especially for quality assurance and quality control of LCDs.

Detection of Cervical Spine Fracture on Computed Radiography Images: A Monitor Resolution Study

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. 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. 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). 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.

Effect of slow display on detectability when browsing large image datasets

Abstract— In this work, the effect of display temporal characteristics on detectability of signals was studied by comparing detection performance with a slow liquid‐crystal‐display (LCD) monitor and a fast, cathode‐ray‐tube (CRT) monitor when browsing multi‐slice image datasets in stack‐mode presentation. Thirteen readers evaluated 200 image sequence pairs in a two‐alternative forced choice experiment. The image sets consisted of three‐dimensional cluster lumpy backgrounds and were presented to the readers in two display devices: a three‐million‐pixel medical color LCD and a color desktop CRT. For the LCD, many inter‐gray‐level transitions are on the order of 50–60 msec, which was almost twice the frame time. The CRT had 2–5‐msec inter‐gray‐level transitions. The reader study was performed with a graphical‐user interface programmed using direct calls to OpenGL libraries to precisely control the browsing speed. The results were analyzed in terms of the difference in reader performance for each reader and each display, between a browsing speed of 20 and 50 frames per sec (fps). Average reader performance difference between 20 and 50 fps was measured to be 0.049 and 0.156 for the CRT and LCD monitors, respectively. The corresponding drop in reader performance associated with slow display was 0.11.

SU‐FF‐I‐50: Development of a 15MsP Super High Resolution Medical Liquid Crystal Display for the Digital Mammography

We developed a new medical display by utilizing our independent sub‐pixel drive (ISD) technology and anti reflection‐coated panel, which realizes resolution of 15M sub‐pixels to accept higher resolution output from modality devices. The ISD technology enables each of three sub‐pixels constituting one pixel element of monochrome displays to be driven independently, and consequently three times resolution enhancement is achieved. We evaluated its sharpness and noise characteristics quantitatively, and performed perceptual evaluations by radiologists by using clinical images for comparison with conventional displays. This new technology was considered effective for the accurate depiction of the fine anatomical structures such as micro‐calcifications of the mammography.

A New Resolution Enhancement Technology Using the Independent Sub-Pixel Driving for the Medical Liquid Crystal Displays

A new resolution enhancement technology using the independent sub-pixel driving technology was developed for the medical monochrome liquid crystal displays (LCDs). Each pixel of monochrome LCDs, which employ the color liquid crystal panels that its color filters are removed, consists of three sub-pixels. In the new LCD system implemented with this new technology, the sub-pixel intensities were modulated according to the detailed image information, and consequently resolution was enhanced three times. Thus the new technology realized a 15 mega-pixels (MP) super high-resolution LCD (SHR-LCD) out of a conventional 5 MP LCD and a 9 MP SHR-LCD out of a conventional 3 MP LCD. Physical measurements and perceptual evaluations performed in this study proved that the achieved 15 MP (through our new technology) was appropriate and efficient to depict the finer anatomical structures such as the micro calcifications in mammography.

High-resolution monochrome liquid crystal display versus efficient household colour liquid crystal display: comparison of their diagnostic performance with unenhanced CT images in focal liver lesions

This study compared the ability of an efficient household liquid crystal display (LCD) and a medical high-resolution LCD to detect small hepatic lesions on unenhanced computed tomography (CT) images. We obtained the images from 100 subjects who had undergone abdominal CT. They consisted of 41 patients with a single space-occupying lesion (SOL) in the liver and 59 control subjects with no SOL. Independently, five radiologists rated their confidence concerning the presence of hepatic SOLs on a continuous scale from 0 to 1. Receiver-operating characteristic (ROC) analysis was performed using the jackknife method using the program LABMRMC. We evaluated the differences in A(z) based on the 95% confidence intervals. The mean A(z) of the five observers was 0.9594 with the efficient household LCD vs. 0.9335 with the medical high-resolution LCD. The difference was -0.0422, and the 95% confidence interval was -0.1101 to 0.0257 (p=0.2203). There was no significant difference in the A(z) value between the two types of LCDs. The diagnostic performance with the household LCD was comparable to that with the high-resolution LCD, implying that the former type of LCD can be used to diagnose CT images.

Image Browsing in Slow Medical Liquid Crystal Displays

Statistics show that radiologists are reading more studies than ever before, creating the challenge of interpreting an increasing number of images without compromising diagnostic performance. Stack-mode image display has the potential to allow radiologists to browse large three-dimensional (3D) datasets at refresh rates as high as 30 images/second. In this framework, the slow temporal response of liquid crystal displays (LCDs) can compromise the image quality when the images are browsed in a fast sequence. In this article, we report on the effect of the LCD response time at different image browsing speeds based on the performance of a contrast-sensitive channelized-hoteling observer. A stack of simulated 3D clustered lumpy background images with a designer nodule to be detected is used. The effect of different browsing speeds is calculated with LCD temporal response measurements from our previous work. The image set is then analyzed by the model observer, which has been shown to predict human detection performance in Gaussian and non-Gaussian lumpy backgrounds. This methodology allows us to quantify the effect of slow temporal response of medical liquid crystal displays on the performance of the anthropomorphic observers. We find that the slow temporal response of the display device greatly affects lesion contrast and observer performance. A detectability decrease of more than 40% could be caused by the slow response of the display. After validation with human observers, this methodology can be applied to more realistic background data with the goal of providing recommendations for the browsing speed of large volumetric image datasets (from computed tomography, magnetic resonance, or tomosynthesis) when read in stack-mode.

Medical displays by using plasma‐beam‐alignment technology

Abstract— Novel anode layer plasma within minimum chamber space was developed for non‐contact alignment process. The plasma‐treated polyimide (PI) surface showed no particle contamination and no micro‐scratches. Surface morphology was investigated by using scanning electron microscope (SEM), an atomic force microscope (AFM), and X‐ray photoemission spectroscopy. The different oxygen‐to‐carbon ratio ([O]/[C] ratio) for XPS spectra indicated a composition change after plasma treatment. Surface pretilt angles were varied from 0 to 2.1° under different plasma exposure times. Finally, a prototype 20.8‐in. QXGA IPS‐mode gray‐scale medical liquid‐crystal display was successfully demonstrated with high contrast ratio, excellent uniformity, and wide viewing angle using this new plasma‐beam‐alignment technique.

Visual Assessment of Angular Response in Medical Liquid Crystal Displays

In spite of having non-Lambertian emission, displays based on liquid crystal technology are becoming popular for medical diagnostic work stations. For all liquid crystal displays (LCDs), the contrast performance varies with viewing direction. Accurate measurements of the angular distribution of light emission require expensive instrumentation and extensive expertise. We investigated the possibility of using a test pattern to visually assess the angular response performance of LCDs. We found that this procedure offers the end user of displays a simple, fast, and relatively consistent technique to verify that the viewing angle performance of the display device is within certain acceptable limits.