British Journal of Radiology (2005) 78, 582-586
© 2005 British Institute of Radiology
doi: 10.1259/bjr/51650129
Ergonomics of digital imaging
S P Prabhu, DCH, MRCPCH, FRCR1,
S Gandhi, DNB, MD, FRCR2 and
P R Goddard, DMRD, MD, FRCR1
1 Radiology Department, Bristol Royal Infirmary, Upper Marlborough Street, Bristol BS2 8HW and 2 Frenchay Hospital, Frenchay Park Road, Bristol BS16 1JE, UK
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Abstract
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There has been an increase in the use of digital imaging in recent years and radiologists have almost universally accepted the use of computers in their day-to-day work. Completely filmless radiology departments, with all reporting being done on visual display terminals and picture archiving and communications systems (PACS) around the department, are already a reality in many places in the UK and other parts of the world. There is a constant need of computers for literature searches on the web, e-mails, communication and preparing lectures and presentations. With this explosive increase in the use of computers in the hospital, it is imperative that the use of computer monitor screens for medical use is optimized in order to avoid eyestrain and fatigue. This is especially important as tired eyes and brains may be more likely to commit errors. We have reviewed the current literature to elaborate a few useful measures that can be taken to minimize the effect of excessive computer use in a soft-copy radiology reporting area on the eyes and the musculoskeletal system. We recommend that optimal placement of computer monitors with user-friendly PACS terminal interfaces will ensure greater acceptability and improve reporting efficiency and accuracy. Good work practices to ensure reduction of reporting errors are highlighted.
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Introduction
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There has been an increase in the use of digital imaging in recent years and radiologists have almost universally accepted the use of computers in their day-to-day work. Completely filmless radiology departments, with all reporting being done on visual display terminals and picture archiving and communications systems (PACS) around the department, are already a reality in many places in the UK and other parts of the world. It is hard to get away from a computer screen even at home with the development of image links for on-call work. There is a constant need of computers for literature searches on the web, e-mails, communication and preparing lectures and presentations.
With this explosive increase in the use of computers in the hospital, it is imperative that the use of computer monitor screens for medical use is optimized in order to avoid eyestrain and fatigue. This is especially important as tired eyes and brains may be more likely to commit more errors. This is of great clinical relevance for radiologists and other healthcare professionals, in terms of risk management and clinical governance. We have reviewed the current literature to elaborate a few useful measures that can be taken to minimize the effect of excessive computer use in a soft-copy radiology reporting area on the eyes and the musculoskeletal system.
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Effects of computer monitors
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Despite early concerns, accumulated evidence from various studies has proven that radiation from visual display terminals is not harmful to the human crystalline lens [1, 2]. The use of computer monitors is however, a visually demanding task that involves sustained periods of intensive close-screen work. There has been an increase in the number of complaints related to eye fatigue such as sensitivity to glare, aching and sore eyes as reported by professionals using computer monitors.
Studies have proven that after prolonged computer use, black and white objects appear tinged with colour for a transient period lasting up to 1 h. This is termed the McCollough effect and is attributed to adaptation of neurons in the cortex that respond to colour and form [3]. Among other common complaints is accommodative spasm – a transient error in refraction due to ciliary muscle spasm that is considered to be a possible cause of functional myopia in computer users [1].
When radiology departments are being redesigned there is a need to highlight the importance of proper ambient lighting and optimal height of furniture used in reporting areas. Recommendations worth considering when designing and working in virtually filmless radiology departments are discussed below.
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Ergonomics and optometric factors
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The main aim when designing the reporting area must be user comfort. Factors to be considered when planning and requisitioning computer desks, tables and chairs are the distance from the user's eyes to the computer screen, desktop and monitor height, room lighting, optimal back support, provisions for disabled users and correct wrist positioning. Most companies will be happy to send information that explains their implementation of ergonomic design. Computer-friendly tables, chairs and desks are paramount in ensuring good reporting, teaching and learning because computer use creates a unique strain on the human body [4, 5].
Position of computer monitors should be slightly further than the reading distance as measured from the eyes when sitting at a keyboard, with the back against the chair (Figures 1 and 2
). It has been shown that visual strain at a viewing distance of 50 cm is greater than at 100 cm (with characters twice as large). The top edge of the monitor should be no higher than eye level. In fact, the current recommendation is for the top edge to be 15–50° below eye level, even for the tall black and white monitors used in modern PACS suites. To adjust the viewing distance to the optimal comfort level, distances between 51 cm and 75 cm with character size of 5 mm are advised [4, 6]. A useful rule of thumb is that if one can read the characters on the monitor, it is not too far away and the top of the monitor should be slightly farther from the eyes than the bottom of the monitor.
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Figure 1. Incorrect position for viewing digital images on monitor. (1) Sub optimal support for the back causing increased strain. (2) Length of the bottom cushion has not been adjusted causing strain on the lower back. (3a) Top edge of monitor is higher than eye level. This increases eyestrain and also leads to increased load on the neck muscles.
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Figure 2. Correct position for viewing digital images on monitor. (3b) Current recommendation is for top edge of monitor to be 15–50° below eye level. (4) Dictaphone is held in the left hand to enable scrolling through image stacks with the other hand. (5) Right forearm and hand are horizontal, with the elbows vertically under the shoulders on the table. No angle must be formed at the wrists. (6) Surrounding light boxes must be switched off.
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The monitor should be placed such that the top line of the text on screen is at eye level, as a slightly downward gaze is more comfortable with vertical inclination of gaze direction between the horizontal and 16° downwards. Placing the monitor too high exposes more of the eye, as a result increasing the rate of tear evaporation. This leads to increased eye fatigue and blurring of vision. There is also a reduction in vertical saccadic rate, which plays a role in decreasing eye fatigue. No specific data could be found in existing literature about the optimal distances for viewing cross-sectional images on computer screens and is perhaps an area for further investigation.
It is also important that monitors are dusted regularly to avoid having to look through a haze, which has been shown to increase eyestrain. Contact lens users are advised to blink more frequently to prevent the eyes from drying. Wearing rigid rather than soft contact lenses is preferred, as hard lenses correct more astigmatism and may increase tear circulation. Bifocal and reading lens users are advised to change over to single-vision spectacles. Doctors who report migraine-like headaches after use of computer monitors are advised to consider the use of polarised or tinted lenses. With increasing computer use, regular eye checks should be made mandatory as part of yearly occupational health check-ups especially for radiologists. It is noteworthy that current legislation requires Occupational Health Departments (OHD) to undertake baseline screening prior to employment, or when employees are identified as working on a regular basis with any visual display unit (VDU) [7]. Staff should then be regularly monitored or reassessed when experiencing vision problems. The health and safety regulations do not expressly include PACS monitors in the definition of visual display units and this is the reason cited for lack of eye testing for radiologists and radiographers in most trusts in the UK.
Lighting and reduction of glare
Typical high-resolution 5 mega pixel (2000 by 2500 pixels) PACS monitors have an output in the range of 60 to 70 foot-lamberts. This is approximately one tenth of the light associated with conventional light boxes, which range between 500 and 1000 foot-lamberts. Studies have documented the importance of an optimal balance between monitor light and background ambient room lighting [8]. Increase in study interpretation times, decreased accuracy and increased fatigue levels were seen when using monitors that were less bright when compared with those with higher luminance. The ambient light should have the same perceived luminance as the monitor itself. Viewing stations should be placed away from windows and overhead lights. It is recommended that text-character brightness should be three times brighter than the background, which should in turn be three times brighter than the ambient lighting. It is also worthwhile to consider the use of designed shields that reduce screen glare especially on older model monitors [2, 5]. In order to ensure indirect and glare free lighting, appropriate wall-mounted or ceiling-suspended lighting should be installed with on/off and dimmer switches available to individual radiologists. Blinds and shades should be available to control outside lighting.
It is important that if paper request forms are used in the department, optimal desktop lighting should be available to read these without disturbing other radiologists in the reporting room. Introduction of electronic patient records should solve this problem.
There may be a need for conventional light boxes to look at previous imaging. This is probably needed even after the whole department has been completely digitized for a few years. The alternative is to digitize the previous plastic film library, which is expensive and time consuming. Modern radiology reporting rooms may have to be set up to accommodate light boxes next to workstation monitors. As long as the ambient lighting is optimized, it shall be possible to go from the digital image to the film image without unduly straining the eyes.
Ergonomics and related musculoskeletal problems
Monitors placed too high or low and incorrectly adjusted chair heights can lead to neck and back problems [4]. Radiologists working on PACS systems have to often twist the neck to look at documents, bend it down to type, and tilt it upward or sideways to look at improperly placed monitors. This places undue strain on the neck muscles as they continuously try to balance the head during these complex, repetitive movements.
It is therefore imperative that the desk height should be adjustable to the user's height. The chair height should be adjusted such that when the fingers are placed on the middle row of the keyboard, the forearms and hands are horizontal, with the elbows vertically under the shoulders on a suitable arm rest and no angle must be formed at the wrists. Fixed height armrests are generally too low. The keyboard should be directly in front of the user and parallel to the edge of the desk (Figures 1 and 2
). Newer ergonomically superior tables with adjustable surfaces for desktop monitors and keyboards are now becoming more readily available. The PACS user should preferably sit upright and the angle and height of the backrest and/or length of the bottom cushion should be adjusted to support the lower back. It is important to adjust the posture throughout the day to relieve any tension on the lower back muscles. A footrest can be invaluable when higher desks are used. A document holder for paperwork such as request cards and previous reports is a useful tool.
Features related to image pre-processing, organization of patient folders and automatic image display sequencing must also be considered. With these features incorporated in the workstation design, the number of steps required for a radiologist to interact with a workstation is minimized. Time spent looking at icons and toolbars can take up to 70% of a radiologist's time, thereby increasing the time taken to report a study. Time spent in retrieving previous images can also increase reporting times. High-resolution colour monitors, automatic retrieval of previous images and voice-based user interfaces are among current research topics in the field of digital workstation design.
Radiologists working in filmless reporting rooms now need access not only to the PACS workstation but also to other equipment such as radiology reporting systems, trust intranet and Internet services in addition to telephones and hospital paging systems to provide an effective reporting service. Such access calls for either an ergonomically designed integrated single workstation with multi-tasking capabilities or multiple platforms that are ergonomically situated.
These aspects should be seriously considered when workstation and furniture purchases are made, especially for new radiology departments. The initial investment towards such equipment will prove to be a wise decision in the long run.
Work practices with relation to ergonomics
It has been proven that the main factor determining visual fatigue in a PACS user is the amount of time spent viewing the display units. Frequent breaks from the screen are recommended to avoid both eye fatigue and neck and back strain. It is recommended that people working at computer monitors should get up and stretch at least every half-hour. It is also advisable to look out of a window during these breaks as this can help relieve accommodative spasm. Where this is not possible (as in most radiology departments), looking into a mirror has the same effect because the viewing distance is doubled [2].
Temperature control in reporting rooms
Computer workstations and monitors tend to raise the temperature in a PACS reading room. In addition to heat generation, humidity is decreased and the air becomes very dry. The most comfortable temperature for sedentary work is between 20°C and 24°C (68–75°F), with a relative humidity between 40% and 60%. However, this ideal is seldom achieved in the average filmless reading room with its numerous workstations.
In Britain, traditional film reading rooms are often converted to filmless reading areas with no accompanying improvement in air conditioning capacity. These factors result in increased heat and poor ventilation. Increased fatigue may result in decreased productivity, more errors and need for longer breaks to refresh the eyes and the body. Exposure of PACS units to excessively high temperatures may result in shortened life of monitors and other components. An increased-capacity air conditioning system should be included in the planning of any PACS reading room. If at all possible, individual controls for temperature and ventilation should be installed at each workstation.
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Is it all worth it?
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In general, CT interpretation with an electronic workstation becomes faster as display area increases and display time decreases. Time-motion analysis has been shown to reduce the overall time required for soft-copy interpretation of CT compared with that of film significantly [9–11]. The study by Reiner et al [11] included time taken to display, interpret, and dictate the individual findings of CT using conventional hard-copy interpretation on a viewbox and soft-copy interpretation, using a four-monitor high-resolution workstation. This study provided evidence that transition to filmless imaging had the potential to improve radiologists' productivity and report-turnaround time. Relative diagnostic accuracy of radiologists in the interpretation of CT scans using a computer workstation in comparison with using film has also been studied [12–14]. Soft-copy interpretation using computer workstations was found to produce statistically significant improvement in combined measurements of sensitivity, specificity, and overall accuracy for chest, brain, and chest-abdominal CT scans compared with film interpretation.
These studies suggest that investment in well designed, ergonomically sound reporting areas will lead to more efficient and accurate image interpretation. A filmless department, if properly planned and combined with the right work practices, should be a valuable asset and therefore must be regarded as a priority in the modernisation of a hospital.
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What do radiologists think?
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In a multi-centre survey of radiologists by Siegel et al [15] experienced in soft-copy reporting, factors judged to be most important in promoting radiologist productivity were room lighting, monitor number, and monitor brightness. Almost all the radiologists indicated that their lighting source was from overhead rather than indirect or portable light sources. Approximately half indicated they had the capability of dimming the brightness of the overhead lighting. They indicated that the most troublesome sources of noise included background noise, other radiologists and clinicians much more than noise from computer monitors, radiographers or patients. Most radiologists did not have chairs that could recline or arm rests. Most did have wheels and the capability to swivel, both of which were judged important. The majority of chairs also had lumbar support, which was also seen to be important. Radiologists commonly adjusted room lighting and their reading chair, but rarely adjusted room temperature or monitor brightness. The median time spent at the workstation before taking a "break" was 1.5 h.
In the study by Rumreich and Johnson [16] designed to gauge satisfaction levels among radiologists with current soft-copy environments, a key finding was low overall satisfaction with soft-copy environments with nearly half (46%) rating themselves as either "very dissatisfied" or "dissatisfied". Consultant radiologists were least satisfied regarding workplace ergonomics, room layout and amount of workspace. Appropriate lighting also emerged as an area of low satisfaction and high importance. 98% of respondents indicated that an "ideal" soft-copy environment would have a positive effect on their efficiency. Recommendations to improve the room layout included compartmentalization of the reading room and availability of the hospital/radiology information system at each workstation. When initially evaluating PACS most radiologists try to duplicate the film environment and believe that multiple monitors are required to maintain the productivity and accuracy of reporting [17]. Changing from a film-based reading environment to PACS environment brings about a change in the overall image delivery technology and there is a concurrent change in the viewing techniques by radiologists [17, 18]. The style of reading films changes with experience. After using PACS, most radiologists prefer using two monitors.
The latest PACS use the now-familiar Windows desktop or even a Web browser to call up historical images, lining them up according to the radiologist's reading preference. Thanks to concurrent advancements in software and hardware graphics capabilities, a single desktop PC and two PACS monitors commonly handle the work of a wall full of light boxes. Hospitals that plan to purchase PACS should ensure that the vendor has multi-planar reconstruction software that optimizes the dual screen displays.
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Ergonomics of speech recognition systems
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Recent introduction of digital dictation and speech recognition systems has highlighted the importance of optimal sound ergonomics including background noise from telephones, other radiologists dictating in the same room and activity in the scanning areas nearby. These can increase the error rates of these systems. This suggests that the use of acoustic dampening materials, such as thick carpets and sound-absorbing panels may have to be incorporated into reporting rooms of the future. Noise cancellation microphones are also proving a real advance in this field. Handling the dictaphone and the PACS monitor mouse simultaneously is challenging and necessitates either use of both hands or hands free dictation sets. It is interesting to note that while speech recognition systems benefit clinicians and patients by reducing time awaiting a diagnostic report and reducing clinic and emergency room waiting time, it does not necessarily benefit the radiologists who use it [19].
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Conclusion
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Implementation of the measures described above should lead to improved workplaces for radiologists and radiographers in filmless departments, reduce eye fatigue, increase efficiency and most importantly, may reduce error rates in reporting.
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Summary
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- Consideration of ergonomic and optometric factors is paramount when designing radiology PACS departments.
- To reduce eyestrain and musculoskeletal fatigue, placement of computer monitors, chairs and desktop units should be optimized.
- Tired eyes may make more errors and every effort should be made to avoid visual fatigue by taking frequent breaks.
- Regular eye checks should be encouraged for radiologists.
- Investment in ergonomically sound radiology PACS workstations must be strongly encouraged.
- User-friendly PACS terminal interfaces and software will ensure greater acceptability and improve reporting efficiency and perhaps accuracy.
Received for publication January 5, 2004.
Revision received January 24, 2005.
Accepted for publication February 11, 2005.
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References
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Abstract
Introduction
