Radiographic viewing conditions at Johannesburg Hospital
1 School of Physics, University of the
Witwatersrand, Johannesburg, South Africa
2 Division of Medical Physics, Johannesburg Hospital, Johannesburg, South Africa
Purpose: To measure the luminance level of X-ray
viewing boxes and ambient lighting levels in reporting rooms as a quality
assurance procedure, and to compare the results with those recommended by the
Directorate of Radiation Control, South Africa (DRC), European Commission (EC)
and Nordic Radiation Protection Co-operation (NORDIC).
Materials and Methods: All the viewing boxes housed
at the Divisions of Radiation Oncology and Radiology of Johannesburg Hospital
had their luminance levels measured using a calibrated photometer. In addition
the room�s ambient light was measured using a photometer.
Results: The mean average luminance was 1026.75 �
548.65 cd m-2 and 3284.38 � 327.91 cd m-2 at the Division
of Radiology and Division of Radiation Oncology respectively. The Division of
Radiation Oncology had an average viewing box uniformity of 7.14% compared to
27.32% at the Division of Radiology. The average ambient lighting was found to
be 66.30 lux and 66.43 lux at the Division of Radiation Oncology and Division
of Radiology respectively.
Conclusion: The radiograph viewing conditions in Johannesburg variably comply with guidelines. This study underscores the need to implement
quality control and quality assurance standards in radiographic image viewing. � 2008
Biomedical Imaging and Intervention Journal. All rights reserved.
Keywords: Luminance, ambient lighting, quality assurance
When light intensity is low, the eye transfers from cone
vision to rod vision. This is because rod vision is more sensitive. At low
light intensities, the eye loses its resolving power or visual acuity . To
achieve optimal visual acuity, it is recommended that the retinal cones receive
an incident luminance of 100 cd m-2 (candela per square metre) .
Given this background it becomes clear that an accurate
interpretation of a radiograph is a function of the viewing conditions and it
will generally decrease as the viewing conditions deteriorate [2, 3]. The
importance of viewing conditions has been overlooked in the process of optimising
the diagnostic radiology process, yet the whole radiographic process can only
be as strong as its weakest link. Many researchers in radiology have
concentrated on dose and image quality optimisation, while ignoring the viewing
conditions. A literature survey has shown that five factors contribute to poor
film reader performance, namely:
- Suboptimal illumination level.
- Excessive pupil dilation.
- Light scatter within the film.
- View box glare.
- Improper ambient light level .
The objective of this study was to measure the luminance
level of X-ray viewing boxes and ambient lighting levels in reporting rooms as
a quality assurance procedure.
Materials and Methods
This investigation included all the conventional viewing
boxes and radiograph viewing areas/reporting rooms in the Divisions of
Radiology and Radiation Oncology at Johannesburg Hospital. The viewing box
luminance (brightness), viewing box luminance uniformity, and the viewing area
ambient lighting were measured using a calibrated Nuclear Associates Precision
Photometer, Model 07-621, manufactured by Fluke Biomedical Radiation Management
Services. The photometer was calibrated at the Nuclear Associates factory in
the United States of America. Measurements were taken at mid-morning, hours
after the viewing boxes had been switched on, with the assumption that the
viewing box light output would have stabilised at the time of measurement.
To assess the viewing conditions and the ambient lighting,
recommendations or guidelines from the DRC, NORDIC (Denmark, Finland, Iceland, Norway and Sweden) and the EC were used as standards [4-6]. These guidelines for
the parameters viewing box luminance, uniformity of viewing box and ambient
lighting are shown in Table 1.
For the purposes of measuring luminance, the view box was
divided into four quadrants so that five measurements could be taken, namely at
the centre of the view box and also at the centre of each quadrant. These
measurements were taken with the photometer positioned flush on the view box.
Viewing box luminance uniformity was determined using the relationship given
where Cmax is the maximum luminance measured
and Cmin is the minimum luminance value measured on the viewing box.
Ambient lighting was measured from a distance of 30 cm
away from a switched-off viewing box [7, 8]. It should be noted that the
European Commission suggests that the ambient lighting be measured at a
distance of 1 m. The measurement distance of 30 cm from the viewing box was
adopted for this study since it approximates the distance between the viewer
and the viewing box in a typical clinical setting. The unit for ambient
lighting is the lux.
A total of 47 viewing boxes were analysed in this study.
From this total, 24 viewing boxes were located in various areas at the Division
of Radiology and the remaining 23 were located at the Division of Radiation
Oncology. Results of the investigation are tabulated in Table 2.
The spread in the magnitude of mean average luminance,
mean central luminance, average uniformity and ambient lighting was quantified
by the standard deviation. The data in Table 2 was compared with the published
guidelines from the DRC, NORDIC and the EC. Figures 1 and 2 show the percentage
of viewing boxes which were in compliance with the guidelines as set out by
different organisations at the Divisions of Radiology and Radiation Oncology
If the whole radiographic process chain is to be fully
optimised, it becomes imperative for viewing box luminance and ambient lighting
to be optimal. Maintaining optimal radiograph viewing conditions is simple and
cheap to achieve. It is thus recommended that optimum radiograph viewing
conditions be in place in order for the radiologist to get the most diagnostic
information from each radiograph. The three organisations� recommendations on
the measured quantities in this study are not in total agreement; as such it
would be a good idea for the radiology community to harmonise these guidelines
worldwide or alternatively adopt one set of guidelines from one organisation.
Radiologists and radiation oncologists at Johannesburg Hospital continue to use these viewing boxes for reporting despite the fact
that these do not comply with the guidelines. Admittedly the detrimental effect
of non-optimal viewing conditions is not as pronounced in general radiography
as it is in mammography. However, there are studies which have proved that
non-optimal viewing conditions affect the radiologist�s ability to detect low
contrast lesions [9, 10]. In addition a number of studies have shown that dental
radiography is affected by non-optimal viewing conditions [11, 12]. The effect
of the continual use of non-compliant viewing boxes can be determined by
conducting observer performance studies or psychophysical experiments.
After 2000 hours of use, the luminance of fluorescent
tubes decreases by approximately 10% . The American College of Radiology
(ACR) recommends replacement of fluorescent tubes after every 18 to 24 months.
This could explain the high level of viewing box luminance uniformity at the
Division of Radiation Oncology as the division has just been recently opened.
The European Commission recommends that the ambient
lighting be measured at a distance of 1 m, thus compliance with the European
guidelines was not analysed. In this present study, ambient lighting was
measured a distance of 30 cm, this being premised on the fact that a distance
of 30 cm approximates the distance between the viewer and the viewing box in a
clinical setting, as one would rarely view a radiography at a distance of 1 m.
Since the viewing box should be switched off during measurement, it is expected
that ambient lighting should not vary with measurement distance.
The average luminance is a better indicator of the viewing
box luminance than the central luminance. This is confirmed by the greater
standard deviation in the mean central luminance than the standard for the mean
average luminance as shown in Table 2.
Screen-film technology still has widespread use in
developing countries and Johannesburg Hospital is no exception. As such it is
imperative to have quality control measures on viewing boxes. Despite the
widespread use of screen-film technology in developing countries, there is a
gradual shift to digital X-ray systems, which could be the ultimate solution to
non-optimal viewing box luminance having a detrimental effect on radiograph
reporting. The use of digital systems paves the way for other viewing options
like the use of video monitors, printing the image on paper and the use of
picture archiving and communication systems (PACS), which have the advantage of
eliminating the cost of film, chemicals and processor equipment. It should not
escape one�s mind that digital imaging systems also have their relevant quality
control requirements needed for optimal viewing of images.
This study showed that the viewing conditions at Johannesburg Hospital were variably in compliance with guidelines from international
organisations. To improve the viewing box uniformity at the Division of
Radiology, it was suggested that the viewing boxes be cleaned and the
fluorescent lamps be replaced regularly. Furthermore, this study underscores
the need of implementing quality control and quality assurance standards in
radiographic image viewing, in support of overall optimisation of the
The authors are grateful to Nicholas van der Merwe of
Gauteng Provincial Health Department for lending them the Precision Photometer
used in this investigation. In addition we would like to acknowledge Professor
Debbie van der Merwe, Director of Medical Physics, Johannesburg Hospital for corrections on the manuscript. Ms Queen Letsoalo at the Division of Radiology is
acknowledged for her assistance.
Figure 1 Bar chart shows the percentage of viewing boxes at the Division of Radiology compliant to different guidelines.
Figure 2 Bar chart showing percentage of viewing boxes at the Division of Radiotherapy complying with different guidelines.
Table 1 Tabulation of published guidelines.
Table 2 Tabulation of the experimental results. The standard deviation in the measured quantity is shown in brackets.
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|Received 3 January 2008; received in revised form 25 February 2008; accepted 10 March 2008
Correspondence: Johannesburg Hospital, Area 248: Medical Physics, Private Bag X39, 2000 Johannesburg, Republic of South Africa. Tel.: +27 11 481 2158; Fax: +27 11 484 9202; E-mail: firstname.lastname@example.org (Thulani Nyathi).
Please cite as: Nyathi T, Mwale AN, Segone P, Mhlanga SH, Pule ML,
Radiographic viewing conditions at Johannesburg Hospital, Biomed Imaging Interv J 2008; 4(2):e17