Effect of room illuminance on monitor black level luminance and monitor calibration

Pathologists light level preferences using the microscope-study to guide digital pathology display use

Background

Currently, there is a paucity of guidelines relating to displays used for digital pathology making procurement decisions, and optimal display configuration, challenging.Experience suggests pathologists have personal preferences for brightness when using a conventional microscope which we hypothesized could be used as a predictor for display setup.

Methods

We conducted an online survey across six NHS hospitals, totalling 108 practicing pathologists, to capture brightness adjustment habits on both microscopes and displays.A convenience subsample of respondents was then invited to take part in a practical task to determine microscope brightness and display luminance preferences in the normal working environment. A novel adaptation for a lightmeter was developed to directly measure the light output from the microscope eyepiece.

Results

The survey (response rate 59% n=64) indicates 81% of respondents adjust the brightness on their microscope. In comparison, only 11% report adjusting their digital display. Display adjustments were more likely to be for visual comfort and ambient light compensation rather than for tissue factors, common for microscope adjustments. Part of this discrepancy relates to lack of knowledge of how to adjust displays and lack of guidance on whether this is safe; But, 66% felt that the ability to adjust the light on the display was important.Twenty consultants took part in the practical brightness assessment. Light preferences on the microscope showed no correlation with display preferences, except where a pathologist has a markedly brighter microscope light preference. All of the preferences in this cohort were for a display luminance of <500 cd/m2, with 90% preferring 350 cd/m2 or less. There was no correlation between these preferences and the ambient lighting in the room.

Conclusions

We conclude that microscope preferences can only be used to predict display luminance requirements where the microscope is being used at very high brightness levels. A display capable of a brightness of 500 cd/m2 should be suitable for almost all pathologists with 300 cd/m2 suitable for the majority. Although display luminance is not frequently changed by users, the ability to do so was felt to be important by the majority of respondents.Further work needs to be undertaken to establish the relationship between diagnostic performance, luminance preferences, and ambient lighting levels.

A systematic review of viewing conditions and monitor specifications in mammography

OBJECTIVES

The purpose of this systematic review was to establish the current status of recommended monitor specifications and viewing conditions in mammography for image acquisition and reporting rooms. A literature search was completed between August 2018 and March 2019 using ScienceDirect, PubMed, Web of Science and MEDLINE databases. An additional manual search was performed to identify relevant guidelines to support the review. Only articles and guidelines written in English were included.

KEY FINDINGS

Results were selected according to the following criteria; articles detailing (i) monitor specification and, (ii) viewing conditions in mammography acquisition and reporting rooms. Twenty-one studies met the inclusion criteria. Six papers described monitor specifications, five described viewing conditions and ten guideline documents were identified from the UK, Europe and the US. Common outcomes were that monitors with 3 or 5 MP resolution seemed to be preferred and at the same time higher illumination levels (>15 lux) were found to decrease the luminance of the monitors and negatively impact the assessment of image quality. Contrary to this, the majority of guideline documents recommended illumination levels above 20 Lux. Finally, there is a lack of guidance for viewing conditions in acquisition rooms.

CONCLUSION

This review did not reveal any strong evidence for the proposed room illumination levels in acquisition rooms. In reference to monitors specifications, there is preference for using higher resolution displays (3 and 5 MP) but again, the evidence is not strong. Moreover, variance exists in the guidelines and that promotes inconsistency in mammography departments.

IMPLICATIONS FOR PRACTICE

This review highlights the lack of standardised guidelines and the need for further research on the viewing conditions and monitor specifications for the acquisition rooms in mammography.

Development and Evaluation of a Novel Point-of-Use Quality Assurance Tool for Digital Pathology

Context.—

Flexible working at diverse or remote sites is a major advantage when reporting using digital pathology, but currently there is no method to validate the clinical diagnostic setting within digital microscopy.

Objective.—

To develop a preliminary Point-of-Use Quality Assurance (POUQA) tool designed specifically to validate the diagnostic setting for digital microscopy.

Design.—

We based the POUQA tool on the red, green, and blue (RGB) values of hematoxylin-eosin. The tool used 144 hematoxylin-eosin–colored, 5×5-cm patches with a superimposed random letter with subtly lighter RGB values from the background color, with differing levels of difficulty. We performed an initial evaluation across 3 phases within 2 pathology departments: 1 in the United Kingdom and 1 in Sweden.

Results.—

In total, 53 experiments were conducted across all phases resulting in 7632 test images viewed in all. Results indicated that the display, the user's visual system, and the environment each independently impacted performance. Performance was improved with reduction in natural light and through use of medical-grade displays.

Conclusions.—

The use of a POUQA tool for digital microscopy is essential to afford flexible working while ensuring patient safety. The color-contrast test provides a standardized method of comparing diagnostic settings for digital microscopy. With further planned development, the color-contrast test may be used to create a “Verified Login” for diagnostic setting validation.

Black perception in a transparent OLED display

Black perception (perceived blackness of gray 0) of transparent OLED displays was studied in this paper. In pre-test, maximum luminances of acceptable black level under various surround conditions were found in a non-transparent display. In the first experiment, the luminance of a transparent patch was compared with that of an opaque one in order to find the effect of transparency on black perception. As a result, participants perceived the transparent patch darker than the opaque one even when the two were in similar luminance levels, which we termed as the "Transparency Effect." In the second experiment, the perceived brightness of gray 0 with various background brightness conditions was investigated to observe the effect of induced black perception. Most participants perceived the luminance of gray 0 darker with brighter background luminance, but some did not. It might result from transparency of gray 0 which had a role as a window presenting the area overlapped with a transparent OLED display.

Performance evaluation of soft copy display systems according to AAPM TG18 protocol

The purpose of this study was to evaluate the display performance of the liquid crystal display monitors according to the American association of physicists in medicine task group 18 (AAPM TG18) protocol at prior and after new calibration. We measured minimum and maximum luminance, luminance ratio, luminance and contrast response, luminance angular and spatial dependency, resolution, veiling glare and chromaticity quantitatively for 33 medical displays. Display noise was evaluated only visually. The mean maximum luminance and luminance ratio were 386 and 273 cd m(-2), respectively. The mean deviation of measured luminance and contrast response from expected response associated with the digital imaging and communications in medicine (DICOM) grayscale standard display function (GSDF) were 9.76 and 2.35 % at prior calibration and 1.23 and 0.26 % after recalibration, respectively. In luminance uniformity test the mean maximum luminance deviation was 16 %. Luminance method was used in the spatial resolution test and the mean percent luminance difference was 12 % at the center. The mean glare ratio was 1 154. The average color uniformity parameter across the display area of each display device was 0.0093. Majority of the test results were in good agreement with the criteria recommended by AAPM TG18 report. Considerable improvement was observed in display luminance and contrast response with respect to expected response of DICOM GSDF after new calibration for some displays.

Comparison of color LCD and medical-grade monochrome LCD displays in diagnostic radiology

In diagnostic radiology, medical-grade monochrome displays are usually recommended because of their higher luminance. Standard color displays can be used as a less expensive alternative, but have a lower luminance. The aim of the present study was to compare image quality for these two types of displays. Images of a CDRAD contrast-detail phantom were read by four radiologists using a 2-megapixel (MP) color display (143 cd/m(2) maximum luminance) as well as 2-MP (295 cd/m(2)) and 3-MP monochrome displays. Thirty lumbar spine radiographs were also read by four radiologists using the color and the 2-MP monochrome display in a visual grading analysis (VGA). Very small differences were found between the displays when reading the CDRAD images. The VGA scores were -0.28 for the color and -0.25 for the monochrome display (p = 0.24; NS). It thus seems possible to use color displays in diagnostic radiology provided that grayscale adjustment is used.

An indicator device for monitoring of room illuminance level in the radiological image viewing environment

Illuminance level in the softcopy image viewing room is a very important factor to optimize productivity in radiological diagnosis. In today's radiological environment, the illuminance measurements are normally done during the quality control procedure and performed annually. Although the room is equipped with dimmer switches, radiologists are not able to decide the level of illuminance according to the standards. The aim of this study is to develop a simple real-time illuminance detector system to assist the radiologists in deciding an adequate illuminance level during radiological image viewing. The system indicates illuminance in a very simple visual form by using light emitting diodes. By employing the device in the viewing room, illuminance level can be monitored and adjusted effectively.

Digital Mammography Image Quality: Image Display

This paper on digital mammography image display is 1 of 3 papers written as part of an intersociety effort to establish image quality standards for digital mammography. The information included in this paper is intended to support the development of an American College of Radiology (ACR) guideline on image quality for digital mammography. The topics of the other 2 papers are digital mammography image acquisition and digital mammography image storage, transmission, and retrieval. The societies represented in compiling this document were the Radiological Society of North America, the ACR, the American Association of Physicists in Medicine, and the Society for Computer Applications in Radiology. These papers describe in detail what is known to improve image quality for digital mammography and make recommendations about how digital mammography should be performed to optimize the visualization of breast cancers using this imaging tool. Through the publication of these papers, the ACR is seeking input from industry, radiologists, and other interested parties on their contents so that the final ACR guideline for digital mammography will represent the consensus of the broader community interested in these topics.

Development of a randomised contrast detail digital phantom for observer detectability study

The accuracy and the efficacy of radiological diagnosis depend, to a large extent, on the conditions under which radiographs and images are viewed. This mainly involves the luminance of the display devices and the ambient room illumination. We report a perceptual study to investigate the relationship between detectability and monitor luminance as well as ambient illuminance. A statistical test pattern was used in this study, and the test pattern was developed using Microsoft® Visual Basic 6. The test pattern contained a set of randomised contrast detail objects, that is, disks of different diameters (0.7, 1.0, 1.4, and 2.0 mm) and contrasts against a black background (2.7, 3.9, 5.5, and 7.8%), simulating lesions in digital images. The receiver operating characteristic (ROC) analysis was used in this study. The results indicated that a set of optimal viewing conditions exists and that it has a significant effect on detectability performance.

Design and Ergonomic Considerations for the Filmless Environment

Planning and executing the redesign of a traditional institutional radiology reading room to conform to the radically different requirements of digital imaging are reviewed, with examples drawn from the authors' experience and from the growing body of literature on this subject. Included are best-practice recommendations and real-life examples on initial design and planning, stakeholder involvement, identifying and hiring consultants, architectural planning, the designation of a radiology point person, rethinking room and workstation design, the selection of ergonomic furniture and fittings, identifying optimal environmental elements, fine tuning and lessons learned, and going digital.

Assessment of PACS display systems

This work describes our experience in reviewing the performance criteria for display systems and how we have implemented a practical approach to the assessment of the workstation environment in a large tertiary care hospital. The acceptance criteria contained in the draft report of Topic Group 18 of the American Association of Physicists in Medicine (AAPM) were used as a basis for assessment of primary and secondary displays. A telescopic photometer was used to measure the maximum luminance and the contrast ratio of the image for the displays used in our radiology department and in the operating and emergency rooms using the standard Society of Motion Picture and Television Engineers (SMPTE) pattern, in ambient light and with light decreased as much as possible. About half of the displays met the AAPM criteria for minimum luminance and contrast ratio in low light. None of the systems met the contrast ratio criteria in ambient light. The challenges in improving the performance and calibrating displays are discussed.

Image quality assurance of soft copy display systems

Image quality assurance has traditionally been a high priority in medical imaging departments. Recently, it has often been neglected with the transition from hard copy (film) to soft copy (computer) display systems, which could potentially result in difficulty in reading images or even misdiagnosis. This transition therefore requires careful management such that comparable image quality is achieved at a minimum. It is particularly difficult to maintain appropriate image quality in the clinical settings outside of medical imaging departments because of the volume of display systems and the financial restraints that prohibit the widespread use of dedicated computers and high-quality monitors. In this study, a protocol to test and calibrate display systems was developed and validated by using an inexpensive calibration tool. Using this protocol, monitors were identified in a hospital in which image quality was found to be inadequate for medical image viewing. It was also found that most monitors could achieve a substantial increase in image quality after calibration. For example, the 0 and 5% luminance difference was discernable on 30% of the piloted display systems before calibration, but it was discernable on 100% post calibration. In addition, about 50% of the piloted display systems did not have the maximum luminance (white level) suitably set, and 35% of them did not have the minimum luminance (dark level) suitably set. The results indicate that medical display systems must be carefully selected and strictly monitored, maintained, and calibrated to ensure adequate image quality.

Validated simple tip to aid eliminating light scatter in viewing overexposed radiographs

INTRODUCTION

Overexposed radiographs can hinder the diagnostic performance of the examining physician. We describe a new, simple technique to aid eliminating light scatter in overexposed radiographs and examine its effect objectively.

MATERIALS AND METHODS

The new technique is simply manufacturing a monocular device out of another rolled up XR sheet and examining the object radiograph through it to mask the light scatter. Controlled environments were created to examine five different radiographs and register the light scatter reduction using a digital high resolution camera.

RESULTS

The light scatter reduction was noted to be statistically significant by using the new technique. (P < 0.001).

CONCLUSIONS

This technique is simple, readily available and avoids the need to repeat radiographs with the associated increased cost, chronological delays and potential radiological harm.

Optimization of reading conditions for flat panel displays

Task Group 18 (TG 18) of the American Association of Physicists in Medicine has developed guidelines for Assessment of Display Performance for Medical Imaging Systems. In this document, a method for determination of the maximum room lighting for displays is suggested. It is based on luminance measurements of a black target displayed on each display device at different room illuminance levels. Linear extrapolation of the above luminance measurements vs. room illuminance allows one to determine diffuse and specular reflection coefficients. TG 18 guidelines have established recommended maximum room lighting. It is based on the characterization of the display by its minimum and maximum luminance and the description of room by diffuse and specular coefficients. We carried out these luminance measurements for three selected displays to determine their optimum viewing conditions: one cathode ray tube and two flat panels. We found some problems with the application of the TG 18 guidelines to optimize viewing conditions for IBM T221 flat panels. Introduction of the requirement for minimum room illuminance allows a more accurate determination of the optimal viewing conditions (maximum and minimum room illuminance) for IBM flat panels. It also addresses the possible loss of contrast in medical images on flat panel displays because of the effect of nonlinearity in the dependence of luminance on room illuminance at low room lighting.

Contrast-detail phantom scoring methodology

Published results of medical imaging studies which make use of contrast detail mammography (CDMAM) phantom images for analysis are difficult to compare since data are often not analyzed in the same way. In order to address this situation, the concept of ideal contrast detail curves is suggested. The ideal contrast detail curves are constructed based on the requirement of having the same product of the diameter and contrast (disk thickness) of the minimal correctly determined object for every row of the CDMAM phantom image. A correlation and comparison of five different quality parameters of the CDMAM phantom image determined for obtained ideal contrast detail curves is performed. The image quality parameters compared include: (1) contrast detail curve--a graph correlation between "minimal correct reading" diameter and disk thickness; (2) correct observation ratio--the ratio of the number of correctly identified objects to the actual total number of objects multiplied by 100; (3) image quality figure--the sum of the product of the diameter of the smallest scored object and its relative contrast; (4) figure-of-merit--the zero disk diameter value obtained from extrapolation of the contrast detail curve to the origin (e.g., zero disk diameter); and (5) k-factor--the product of the thickness and the diameter of the smallest correctly identified disks. The analysis carried out showed the existence of a nonlinear relationship between the above parameters, which means that use of different parameters of CDMAM image quality potentially can cause different conclusions about changes in image quality. Construction of the ideal contrast detail curves for CDMAM phantom is an attempt to determine the quantitative limits of the CDMAM phantom as employed for image quality evaluation. These limits are determined by the relationship between certain parameters of a digital mammography system and the set of the gold disks sizes in the CDMAM phantom. Recommendations are made on selections of CDMAM phantom regions which should be used for scoring at different image quality and which scoring methodology may be most appropriate. Special attention is also paid to the use of the CDMAM phantom for image quality assessment of digital mammography systems particularly in the vicinity of the Nyquist frequency.

Soft-Copy Reading of Digital Chest Radiographs

OBJECTIVE

We sought to evaluate whether soft-copy reading of simulated pulmonary chest lesions is influenced by ambient light and automatic optimization of cathode ray tube (CRT) monitor luminance.

MATERIALS AND METHODS

Four types of simulated lesions (nodules, lines, micronodules, and patchy opacities) were superimposed over an anthropomorphic chest phantom. Lesion detection with soft-copy reading was assessed using a high-contrast grayscale 2K CRT monitor under the following conditions: (1) subdued lighting (<50 lux); (2) normal lighting conditions (450 lux) without, and (3) with a sensitivity modulation to automatically adjust the CRT luminance to the increased amount of ambient light. Reading data were analyzed according to receiver operating curve. Significance of differences was tested using an analysis of variance for repeated measures.

RESULTS

Ambient room light of 450 lux did not significantly influence the detection of nodules and patchy opacities. However, bright ambient light significantly decreased detection of micronodules (0.60 vs. 0.74) and lines (0.52 vs. 0.66) relative to subdued lighting conditions. Automatic luminance adjustment could compensate the effect of ambient light for the micronodules (0.77) but not for the lines (0.53).

CONCLUSION

Bright ambient light significantly decreases detection of small low-contrast structures. This may be partially but not completely compensated by an automatic luminance adaptation.