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Commentary |
Department of Radiology, University of Malaya Medical Centre, 59100 Kuala Lumpur, Malaysia
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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-2. To achieve this, the brightness of the film illuminator should be between 2000 and 4000 cdm-2 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-2). 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-2). 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 increase, diagnostic accuracy declines and the degree of fatigue also increases. The greatest problem in any reading area is that of lighting: glare, reflection, scatter and inability to control lighting levels. There appears to be unanimous agreement in support of the view that low levels of room illuminance are necessary for optimal viewing conditions. A few studies have demonstrated that luminance does not have much influence on detection and subsequent diagnosis [8–10]. More research is needed to confirm this finding.
With the above scenario in mind, we recommend the following:
It would be appropriate for the British Institute of Radiology and the Institute of Physics and Engineering in Medicine to take the lead and set up a joint working party to address this crucial issue that has a significant impact on radiological diagnosis.
Received for publication October 20, 2000. Revision received January 24, 2001. Accepted for publication March 7, 2001.
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This article has been cited by other articles:
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  C. T. Lau and W. B. Gefter The Electronic Viewbox Am. J. Roentgenol., March 1, 2005; 184(3): 1021 - 1023. [Abstract] [Full Text] [PDF]
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 E McCarthy and P C Brennan Viewing conditions for diagnostic images in three major Dublin hospitals: a comparison with WHO and CEC recommendations Br. J. Radiol., February 1, 2003; 76(902): 94 - 97. [Abstract] [Full Text] [PDF]
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