British Journal of Radiology (2003) 76, 94-97
© 2003 British Institute of Radiology
doi: 10.1259/bjr/92036272
Viewing conditions for diagnostic images in three major Dublin hospitals: a comparison with WHO and CEC recommendations
E McCarthy and
P C Brennan, PhD
UCD School of Diagnostic Imaging, Herbert Avenue, Dublin 4, Ireland
Correspondence: P C Brennan, UCD School of Diagnostic Imaging, Herbert Avenue, Dublin 4, Ireland
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Abstract
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Accurate interpretation of X-ray images is dependent on image viewing conditions. A recent study in Ireland demonstrated that even with the advent of digital departments the majority of images are still viewed using viewing boxes. This investigation aimed to measure average viewing box brightness, percentage uniformity and ambient light levels in radiology and radiographer viewing areas and wards within three major Dublin hospitals. The results were compared with published recommendations by the World Health Organization and Commission of the European Communities. Following analysis of more than 4650 measurements, it was shown that mean values for average viewing box brightness for all departments failed to achieve recommended levels. Only one third of areas met the most lenient guideline for percentage uniformity. Ambient lighting was shown to be unacceptable for ward areas. For all three parameters, radiology areas generally fared best, with wards gaining the poorest scores. Following a 3 min cleaning regimen of viewing boxes, the average brightness and percentage uniformity were improved in 100% and 80%, respectively, of viewing boxes, but average brightness values remained below recommended levels. The importance of comprehensive quality assurance programmes for viewing boxes has been highlighted so that visualization of images is not reduced to sub-optimal levels. The need for consistent and more informative recommendations has been emphasized.
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Introduction
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Diagnostic efficacy in X-ray departments relies heavily on the conditions under which radiographs are viewed. Whilst much emphasis is placed within departments on optimizing all other parts of the imaging chain to ensure the consistent production of high quality images, it appears that relatively little emphasis is placed on viewing conditions [1]. Although digital equipment and procedures are proliferating at a rapid pace, in Ireland the majority of X-ray images are still interpreted from film mounted on viewing boxes [2, 3].
To maximize visual acuity, it is important that the retinal cones receive an incident luminance of 100 candela m-2 (cd m-2) [4, 5]. In diagnostic radiology, viewing boxes with low brightness will reduce the light reaching the eye, limiting visual acuity, thus reducing the ability to carry out adequate assessment of radiographs compared with a viewing box operating under optimum conditions [6]. Viewing boxes should also demonstrate consistent spatial illumination, otherwise areas of the image will transmit less light than adjacent areas, even though optical densities in the two areas may be the same. It is equally important that extraneous lighting in the form of excess ambient lighting should be minimized to ensure that subjective appreciation of image contrast is maximized [7, 8]. To facilitate assessment of all these viewing condition parameters a range of guidelines are available [9–11], which are summarized in Table 1
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A study carried out in the mid 1990s by Cooney et al [12], demonstrated that viewing conditions in two Dublin hospitals were less than ideal with no viewing boxes meeting the minimum criteria specified in the 1990 Commission of the European Communities (CEC) working document [4]. The need for regular and comprehensive quality assurance (QA) schedules was highlighted. Since that study, the CEC document, European Guidelines on Quality Criteria for Diagnostic Radiographic Images [11], has been published and it is the aim of this investigation to examine the impact of that document on current viewing conditions in Dublin hospitals and determine if viewing conditions have improved since the mid 1990s. The effect of a simple viewing box cleaning procedure on brightness levels and uniformity will also be established.
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Materials and methods
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All six general Dublin hospitals were considered for the study. One of these hospitals operates a picture archiving and communication system (PACS) and therefore did not have viewing boxes. Of the five remaining hospitals three were randomly chosen. These hospitals will be referred to as A, B and C. Within each hospital three key areas were identified as having viewing boxes. These were radiologists' offices, radiographers' viewing areas and ward areas. A minimum of 30 viewing boxes was randomly chosen from each area. All viewing boxes chosen were used in each area on a daily basis.
Three viewing condition parameters have been identified in guidelines and previous studies [4, 9–13]: viewing box brightness; viewing box brightness uniformity; and ambient light levels. Each of these was measured in this study. In previous work [13, 14], viewing box brightness was measured using the centre of the viewing box. Early in this study however, it became apparent that a large variation existed in luminance levels between the centre and the periphery of each viewing box and a single measurement could not adequately predict the brightness levels for all areas. It was decided therefore that, in addition to central viewing box measurements, a number of measurements would be made from different areas of the viewing box. This was facilitated by using a specifically designed test tool consisting of a black card, the area of which, 35 cm x 45 cm, was either bigger than or equal to all viewing boxes involved in the study. Two lines were drawn that bisected the length and width of the card and two further diagonal lines were drawn between the corners. A hole of 2 cm was then produced in the centre of the card and two further holes along each line from the centre to the edge at 40% and 80% intervals (Figure 1). The card was attached to the front of each viewing box and measurements were taken through each hole. This arrangement ensured that measurements were from the same locations on all viewing boxes (±3%). The mean value of all readings was calculated for each viewing box and expressed in candela metre-2.
Viewing box brightness uniformity was calculated from the highest and lowest reading obtained from each viewing box. Uniformity was described as the maximum deviation of brightness expressed as a percentage and was calculated from the following formula [15]:
where Cmax equals the maximum brightness value and Cmin the smallest brightness value.
Ambient lighting in all the areas detailed above was measured at a distance of 30 cm from the viewing boxes with all viewing boxes switched off [12, 13]. Ambient light levels were expressed in lux.
All parameters were measured using a Harpell Associates (Ontario, Canada) photometer, model 07-621.
Once the main study was completed, 10 viewing boxes, which had already been measured, were then chosen at random and cleaned. The cleaning consisted of cleaning the front and back surface of the perspex cover, cleaning the bulbs and also the reflective surface within the light box. The brightness was re-measured and new values were compared with previous values obtained for the same boxes.
All data were compared with published guidelines [9–11]. Mean number of bulbs within each light box and percentage of bulbs that were working in each area was recorded along with details of windows and lights in viewing areas.
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Results
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In the main part of the study 17 measurements were obtained from each of 30 viewing boxes from each department within each hospital, resulting in a total of 4590 measurements. A further 96 measurements were performed on ambient lighting.
Large variations were noted within each department, between departments of the same hospital and between hospitals for the same department type. The measurements gathered are summarized in Table 2.
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Table 2. Summary of mean viewing box and ambient lighting values in each department. Minimum and maximum values for each area are shown in parentheses
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A number of differences were seen between areas for technical details on light box and ambient light conditions. These details are summarized in Table 3.
10 viewing boxes were then randomly chosen and cleaned as described in the methodology. All viewing boxes demonstrated an improvement in average brightness following cleaning, with percentage uniformity improving in 8 of the 10 boxes (Table 4).
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Discussion
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Recent visits to a number of hospitals to establish national reference dose levels demonstrated that approximately 90% of hospitals produced hard copy images [2, 3]. This highlights the importance, even with the advent of digital technology, of ensuring that viewing boxes are not operating below optimum levels.
In the current study, viewing box brightness data demonstrated that the average brightness level for each box was up to 22% less than central brightness values, emphasizing the importance of standardizing this measurement. The average value appears to be a more useful indicator of viewing box performance since many areas within a radiographic image need to be studied thus requiring optimum brightness values across the image. The average and central brightness values obtained in this work demonstrate that all departments were operating below any of the published guidance levels with only a small number of individual viewing boxes reaching the most lenient levels specified by the World Health Organization (WHO). It was noted that the radiology areas had the highest values when compared with the ward areas in all hospitals and when compared with the radiography areas of hospitals B and C. The variation in brightness levels between the different areas may be linked to the number of operational bulbs within the viewing boxes, since in two out of the three hospitals 100% of radiology bulbs were working, compared with 80–88% in ward areas.
The percentage of bulbs that were operational may also explain the variation in viewing box percentage uniformity that was seen between areas within each hospital. Radiology areas again fared better with two of the three hospital demonstrating a level within the guidelines specified by the CEC in 1997 [11], whilst none of the ward areas achieved acceptable levels. It is important to note that even though two radiology areas and one radiography area achieved the level stated by the CEC, none reached the more stringent level specified by the WHO. All areas in hospital A failed to reach either of the recommended levels.
The ambient lighting measurements were more encouraging than the previously discussed findings with all areas apart from two ward areas achieving the WHO guidelines. It should be stated that for this parameter, only the WHO guidelines are relevant since ambient lighting in this work was measured at a distance of 30 cm from the viewing box, as recommended by the WHO, unlike the 100 cm advised by the CEC. Shielded windows and switched off lights are the most likely explanations for the lower ambient lighting consistently recorded in radiology departments compared with the other areas.
Cleaning the viewing boxes was shown to be an important way of improving viewing conditions. When 10 viewing boxes underwent a 3 min cleaning procedure, average brightness in all boxes was improved and in 80% of viewing boxes better uniformity was demonstrated, highlighting the usefulness of including this procedure in departmental quality assurance protocols. It is important to acknowledge that even though cleaning did improve viewing conditions, average brightness still failed to reach recommended levels, showing that other action is required to further improve the brightness. This may include changing the bulbs, checking the colour temperature of all bulbs, replacing older light boxes that have very poor illumination properties and checking transmission levels of the perspex front of viewing boxes. Any corrective procedure should be followed by acceptancy tests and regular constancy checks.
As seen above a range of guidelines exist for brightness and uniformity of viewing boxes [9–11]. Recommendations for brightness of the viewing box range from 1500 cd m-2 [9] to 4000 cd m-2 [10], whilst uniformity reference levels vary from 15% to 30% [9, 11]. Also, even though this study has demonstrated large differences between central and average brightness levels, it has been previously specified that central brightness values should be calculated. That would appear to be a poor predictor of the viewing box performance [13, 14]. To facilitate relevant and accurate assessment of locally derived data it would be helpful if the wide range of recommendations was narrowed and more informative methods of calculating viewing box brightness were introduced.
Accurate diagnoses from hard-copy radiological images depend upon optimum viewing conditions and this has been highlighted in several publications where sensitivity and specificity has been shown to be reduced with inappropriate illumination [10, 16, 17]. The current study demonstrates the importance of regularly checking viewing box and ambient lighting conditions and a meeting is being arranged to discuss the results with Irish imaging departments.
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Conclusion
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This study demonstrates that average brightness values and percentage uniformity of viewing boxes in the Dublin departments showed poor compliance with published guidelines and have not improved since the study by Cooney et al, in the mid 1990s [12]. The lack of agreement between average and central brightness measurements highlights the need for clear measurement technique standards. Also, due to the variety of guidelines, it is unclear as to which recommendation should be followed. Ambient lighting was shown to be in acceptable levels for all areas except the wards. Cleaning procedures are an important way of improving viewing box lighting but this alone did not achieve the average brightness that is required. A rigorous and regular quality assurance programme for viewing conditions is required so that diagnostic efficacy of images is not reduced.
Received for publication June 13, 2002.
Revision received September 22, 2002.
Accepted for publication January 3, 2003.
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References
|
|---|
- Abdullah BJJ. In the eyes of the beholder: what we see is not what we get. Br J Radiol 2001;74:675–6.[Abstract/Free Full Text]
- Johnston DA, Brennan PC. Reference dose levels for patients undergoing common diagnostic Xray examinations in Irish hospitals. Br J Radiol 2000;73:396–402.[Abstract]
- Brennan PC, Johnston D. Irish X-ray departments demonstrate varying levels of adherence to European guidelines on good radiographic technique. Br J Radiol 2002;75:243–8.[Abstract/Free Full Text]
- Commission of the European Communities. Quality Criteria for Diagnostic Radiographic Images. Working document (2nd edn), XII/173/90. Brussels, Belgium: CEC, 1990.
- Hartmann E, Stieve F-E. Quality control of radiographic illuminators and associated viewing equipment. In: Moores BM, Stieve FE, Eriskat H, Schibella H, editors. Report 18, Technical and Physical Parameters for Quality Assurance in Medical Diagnostic Radiology. Tolerances, Limiting Values and Appropriate Measuring Methods. London: British Institute of Radiology, 1989:135–7.
- Overington I. Physiological conditions for the effective interpretation of radiographic images. In: Moores BM, Stieve FE, Eriskat H, Schibella H, editors. Report 18, Technical and Physical Parameters for Quality Assurance in Medical Diagnostic Radiology. Tolerances, Limiting Values and Appropriate Measuring Methods. London: British Institute of Radiology, 1989:129–35.
- Alter A, Kargas GA, Kargas SA, Cameron JR, McDermott JC. The influence of ambient and viewbox light upon visual detection of low contrast targets in a radiograph. Invest Radiol 1982;17:402–6.[Medline]
- Abildgaard A, Notthellen JA. Increased contrast when viewing radiographic images. Radiology 1992;185:475–8.[Abstract/Free Full Text]
- WHO. Quality Assurance in Diagnostic Radiology. Geneva, Switzerland: World Health Organisation, 1982.
- European Guidelines on Quality Criteria for Diagnostic Radiographic images. EUR 16260 EN. Brussels, Belgium: CEC, 1996.
- Criteria for acceptability of radiological (including radiotherapy) and nuclear installations. Radiation Protection No. 91. Luxembourg: CEC, 1997.
- Cooney P, Davis C, Chua JBY, van der Putten W, Malone JF. Survey of image viewing conditions for x-ray film. Radiat Prot Dosim 1995;57:305–8.[Abstract]
- Guibelalde E, Vano E, Llorca AL. Quality assurance of viewing boxes: proposal for establishing minimum requirements and results from a Spanish quality control programme. Br J Radiol 1990;63:564–7.[Medline]
- Baulm A. WHO-Training Workshop on Quality Control and Assurance in Diagnostic Radiologic. Practical exercises: World Health Organisation report. Geneva, Switzerland: WHO, 1982.
- National Electrical Manufacturers Association. Standards for the Performance of Radionuclide Imaging Devices. Publication No. NU-1-1980. Washington DC: NEMA, 1980.
- Krupinski E, Roehrig H, Furukawa T. Influence of film and monitor display luminance on observer performance and visual search. Acad Radiol 1999;6:411–8.[CrossRef][Medline]
- Patel N, Rushton, VE, Macfarlane TV, Horner K. The influence of viewing conditions on radiological diagnosis of periapical inflammation. Br Dent J 2000;189:40–2.[CrossRef][Medline]
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Abstract
Introduction
