Monitor Luminance Research Articles

Influence of monitor luminance change on observer performance for detection of abnormalities depicted on chest radiographs.

To investigate how changes in luminance affect the detection accuracy of radiologists viewing chest radiograph images on high-resolution CRT monitors. Thirteen radiologists performed a detection task for 11 chest radiograph images with simulated nodules on a monitor with 11 luminance conditions (the maximum luminance ranges from 157.4-369.0 candela/m2) simulating CRT degraded by long-term usage, under the ambient illumination of 200 lux; the observation order was always from the darkest to the brightest. There was a statistically reliable effect of the 11 monitor display conditions on the detection of nodules (P < 0.001). In the conditions in which the maximum luminance of the CRT was 60.7% or below that of the standard display luminance, the correctly detected nodule number reliably deteriorated. The luminance change in CRT monitor display under long-term usage will have a detrimental effect on nodule detection performance in chest radiograph images.

SoftCopy Display Quality Assurance Program at Texas Children's Hospital.

With growing dependence on picture archiving and communication systems for viewing images, a quality assurance program to monitor the condition of workstation displays has become increasingly important. At present there is no universally accepted program for PACS, but there are groups such as DICOM Working Group 11 of the ACR-NEMA and AAPM Task Group 18 that are working on image quality guidelines for interpretation from soft-copy displays. Texas Children's Hospital (TCH) is developing our own quality assurance program. Data is being collected to determine the appropriate frequency of calibration, the useful life of the displays, appropriate manufacturers, and model-dependent limits on maximum and minimum luminance (black level), symptoms of degradation, and monitor cleanliness. Our system includes a variety of monitors manufactured by Sun, AFP, Siemens, Image Systems, Barco, and Orwin. We are presently collecting data on individual monitor luminance functions but have not yet initiated service calls based on deviation from the DICOM Part 14 Grayscale Display Function (GSDF). The GSDF was intended to produce a grayscale in which driving levels produce changes in luminance that are perceptually equivalent throughout the entire luminance range for a specific test target. Our data is based on measurements of luminance from a digital Society of Motion Picture and Television Engineers (SMPTE) test pattern, which is a standard used by many other institutions. TCH's biomedical engineer measures luminance data each month from the display of the SMPTE pattern and record the results in a spreadsheet. The engineer also makes subjective evaluations of sharpness, geometric distortion, and artifacts. When a monitor's luminance falls outside of arbitrary 10% limits of maximum or minimum luminance, then a service call is placed to the vendor. The luminance check by the biomedical engineer is used to verify both routine and unscheduled calibrations. In addition to the monthly monitor checks, the vendor calibrates the monitor every three months. The vendor checks the following: width and height of display, focus and position of image, SMPTE test pattern, and a graph of the GSDF Index produced by an automatic calibration software by the video driver card. Monitors are also cleaned occasionally for dust, fingerprints, ink, and pencil marks, which accumulate with routine use. This paper reports data collected to date on luminance drift, as well as conclusions on appropriate frequency of test and calibration, and our experience with monitor useful life.

In the eyes of the beholder: what we see is not what we get.

Today, imaging is at the heart of the health care system. Accuracy of diagnosis and ultimately the efficacy of radiological diagnosis greatly depend on the conditions under which radiographs and images are viewed. These conditions include the luminance of the display devices (view boxes and display monitors) as well as the ambient room illumination or the amount of light falling on the viewing surface. Extensive psychophysical and clinical research has established the fact that lesion detectability declines when viewing conditions are not optimized. Sad to say, although viewing of radiographic images is a vital link in the imaging chain, it is not accorded much importance and the radiology community has given it scant attention. The fact that there is no one apparent internationally agreed standard for clinical practice underscores the lack of focus on this issue, although attempts have been made to establish standards and guidelines. Quality control of view boxes has been recommended in the UK, and a luminance uniformity standard is given in ‘‘Practical guide to quality assurance in medical imaging’’ [1]. This standard stipulates that the brightness levels of the centre and in each quadrant of the view box should be within 10% of the mean value. It is also recommended that the level of illumination in the room under normal clinical film viewing conditions should not exceed 100 lux. One of the viewing conditions stated by the European guidelines [2] is that ‘‘The light intensity incident on the viewer’s eye should be about 100 cdm. To achieve this, the brightness of the film illuminator should be between 2000 and 4000 cdm for films in the density range 0.5 to 2.2.’’ However, these recommendations have not been generally adopted as part of the routine quality assurance programme of radiology departments. Both the Royal College of Radiologists [3] and the American College of Radiology (ACR) [4] guidelines and standard for teleradiology recommend monitor luminance of at least 50 ft-L (171.3 cdm). However, the ACR merely suggest that ‘‘Care should be taken to control lighting in the reading room to eliminate reflections in the monitor and to lower the ambient light as much as is feasible.’’ The most comprehensive guidelines on view box and viewing conditions is the mammography quality control established by the ACR and the American Cancer Society [5]. They recommend that ‘‘The luminance of a mammographic viewbox should be at least 3,000 to 3,500 nit (cdm). The room ambient illumination level should be 50 lux or less.’’ A summary of all international regulations and guidelines has been compiled by Smartlight Inc. [6]. Perhaps it is pertinent to mention a new generation of digital view boxes that meet these requirements and promise to improve diagnostic efficacy [6]. Even though there is a trend towards increased utilization of soft copy viewing, the vast majority of facilities worldwide, especially those in less developed countries, still rely on view boxes to display and read films. As computed radiography, picture archiving and communication systems (PACS) and teleradiology gain popularity, the luminance of display monitors and the quality of soft copy reporting become important quality issues. In the past, the number, location and size of rooms were important considerations. Today, soft copy requires additional considerations, for example lighting and ergonomics. These considerations have an impact on the radiologist’s comfort, accuracy and speed in soft copy interpretation [7]. As ambient room illuminance levels Received 20 October 2000 and in revised form 24 January 2001, accepted 7 March 2001. The British Journal of Radiology, 74 (2001), 675–676 E 2001 The British Institute of Radiology