We spend a lot of money ensuring we are using quality ultrasound machines, often with the latest transducer and beam forming technology. We recognise that to obtain quality data we need to spend years on our education, and practicing our craft to develop the fine-motor skill and cognitive abilities to obtain the highest quality information of the heart. But, too often we then use cheap, poorly set-up monitors to view the images. This can be a bit like looking through a dirty windscreen (how do expect to drive the sportscar, if you can’t see properly). Many sonographers are simply unaware of the difference a properly set-up display monitor can make to our work. Proper monitor settings play a crucial role in QA processes in the echo lab, yet most of us take this aspect of our imaging for granted.
The best imaging is limited by the quality of the displayed image.
To help teach us more about monitors, I recently spent 5-minutes talking with Jeremy Daalder, owner of ImageScience.
Since 2001, Image Science has been offering digital imaging products, services and expertise to photographers and printers around Australia. ImageScience is a leading supplier of high-quality medical grade monitors and calibration equipment. Jeremy provides invaluable advice for setting up imaging labs, ensuring the best match of products with the available budget, and takes a personal interest in his client’s projects.
Hi Jeremy, thank you for taking the time to chat with Echo.Guru and share your knowledge of imaging monitors.
Firstly, what is the basic difference between “standard consumer” monitors that come with a computer purchase compared with a “medical grade” monitor?
Medical grade monitors are (should be!) – more accurate. Consumer monitors are made to be pleasing, which generally means very bright and contrasty, so that movies/games etc. are presented with maximum ‘pop’ but with little regard for accuracy. Detail in deep shadows and high highlights are sacrificed for ‘inky blacks’ and ‘clean whites’, and when monitors run that brightly they tend to lack uniformity – that is, they exhibit changes in brightness/colour across the field of display.
If you’re using a monitor for medical imaging/diagnostics (or any high quality imaging application, such as photographic editing) – these are precisely the characteristics you DON’T want in a monitor. You want tones and colours to be accurately placed. You want those accurately placed tones to appear the same no matter where the image is on the screen (i.e. you want the screen to be uniform). You want the monitor to show maximum detail available, with no sudden drop offs to detail-less black.
Medical monitors will generally support some sort of calibration – the more basic ones simply calibrate well with standard monitor calibrators, but better models offer full DICOM calibration. DICOM is the main standard in the medical world for placing tones at the correct level. Basically, if you’re DICOM calibrated you can be sure you’re seeing detail as it was meant to be seen – which is of course very important in a diagnostic context.
Consumer grade monitors are made for shorter sessions. Their high brightness is fatiguing to your eyes, and most of them offer crude brightness control. If you do lower the brightness levels, a lot of them flicker. This is due to LED backlights and PWM modulation – technically you won’t see this with the naked eye, but the backlight is in fact being power cycled many times per second. As the monitor gets dimmer, the off cycle gets longer versus the on cycle, and this leads to sub conscious and uncomfortable flicker.
High quality monitors almost always have anti-glare (matte) coatings – very similar to what you get on high end photographic lenses. Consumer monitors use gloss as a cheap and nasty way of increasing contrast – but this means half of what you’re seeing in your screen is the shirt you’re wearing!
Some medical grade monitors have very high resolution but this is in fact much less important in practice than accurate display. One can zoom in for more detail, but if your screen is fundamentally inaccurate this detail is, in turn, unreliable – so while 4K monitors are appearing now, it will be later in 2015 and beyond that really good, accurate 4K monitors will appear and start to reach reasonable prices. The best currently is the Eizo EV32 model.
Does it really make a difference to the image quality? For ultrasound, do I really need the “Rolls-Royce” DICOM compliant monitors.
Really ‘Rolls Royce’ monitors are another level again and sold to professional photographers and used in broadcast video etc. What you do need is a mid level monitor with ideally DICOM calibration. This means, for example, the NEC P or PA Ranges. Most medical imaging purposes are well suited to the P range – the PA range is higher quality again and offers a significantly expanded colour gamut, but this tends to be of more interest to creative folks. Of course we find a lot of people with an interest in medical imaging are keen photographers as well, so you can ‘kill two birds’ with something like a PA272W or the crème de la crème Eizo CG277. These support easily switching between multiple calibrations so you can have a medical mode for your work needs and a photographic mode for your play needs! The Eizo is particularly awesome and would fall in to the Rolls Royce category I guess, with full in built and totally automatic calibration!
The reason you want DICOM is so that the most basic aspect of your monitor’s display is properly calibrated for medical imaging – basically the tonal range from black to white is all put in the right spot so you do detail properly. Without being too dramatic, I have been told this can aid greatly in accurate diagnostic uses.
I use a dual monitor set-up for reviewing the ultrasound images. The images seem a slightly different colour and brightness between the two screens. Does this mean I need a new monitor?
Perfect monitor matching is extremely difficult. Basically, you will never get two monitors – even two of the exact same type bought on the same day – to be a 100% perfect match. However if you want them to match, calibrating your monitors is the best approach and you can get quite close. The reason you can’t get them exactly matching is a complex mix of factors to do with viewing angles, manufacturing tolerances, and the fact the human eye is ridiculously good at seeing very very small differences in colour when presented with large patches of colour. However if you are not displaying single tones, but rather continuous tone images, the match can be excellent once both are properly calibrated. As a practical example – say you use a grey backdrop on both screens – it will never be 100% identical to the eye and this can seem very frustrating. But if you bring up two x-rays they will appear effectively identical! The trick is to use black as your backdrop!
Do all monitors allow calibration of the image settings?
No, some have no controls at all, and most have very poor controls only offering coarse adjustments. Most monitors are in fact ‘profiled’ rather than calibrated, meaning they are measured and crude software corrections are made in the video card to correct their display. Better monitors allow you to actually calibrate directly using the monitor’s hardware (AKA Direct Hardware Calibration) – absolutely one of the key things that distinguishes better monitors.
Really accurate display requires complex, subtle corrections to tones, often in multiple directions at once. This requires monitor support in the form of 3D look up tables – which only the better monitors like NEC PA and Eizo CG offer.
What equipment is required to perform the calibration process?
This depends on the monitor.
If you’re using a standard monitor, you can use something like the Spyder4 Pro, or better the i1Display Pro, to profile your screen. This will allow you to get better results with your current equipment and is the first and most basic step towards accurate display.
If you’re using a better monitor, you will be able to use direct hardware calibration. Each maker has their own software for this, and you would generally pair it with a good sensor like the i1Display Pro. Thankfully, you can generally share this software/device within your office/lab so you can, say, buy 6 screens and just one calibration system. The process takes about 10 minutes per screen, and you do it every couple of months or so.
Can I set up all the monitors in the lab to have the same calibration settings?
Yes, definitely, and this is a good idea assuming they’re all used for the same purpose. This will bring them as close as possible. If you want to get really fancy this can be done at the network level with all machines self calibrating automatically periodically – the Eizo CG range can do this.
How often should we calibrate our monitors? Is this a once-off process or should it be done routinely?
Monitors, being simple devices with LCD filters in front of changing backlights, will drift over time. They’re getting steadier so most people calibrate every two or three months now, although with older monitors once a month or more was typical. The software will remind you when the process is due, it depends not so much on calendar time as monitor (backlight) usage time. But you definitely do want to do this on an ongoing basis – drift can be as much as 1% a months, so after 6 months you can have a significant shift in display and if you’re not taking this in to account, you can definitely run in to issues.
What is the approximate life expectancy of a monitor?
NEC monitors have a three year warranty and Eizo five. We find most people replace screens around that 5 year mark on average. This is more because technology improves more than the monitor wearing out – most will calibrate well beyond 10000 hours (roughly ten years) of actual use. I have heard the figure of 30000 hours used, but I think that’s a bit ambitious in practise. If you think 5 – 7 years of professional use, you’d be about right.
Finally, the best quality image is hard to see through all the dust on my screen. What do you recommend for cleaning monitors?
Eizo screen cleaner is excellent and safe for all LCDs.
Jeremy, thank you again for your time. This insight has been invaluable.
Got more monitor questions or a suggestion for who I can spend “5 mins with…”?? Leave a comment below…
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