September 2014

On Displays: How Monitor Technology Is Evolving in Imaging
By Beth W. Orenstein
Radiology Today
Vol. 15 No. 9 P. 12

Advances in technology allow radiologists to acquire images from most modalities with greater speed, clarity, and dimension than ever. The displays radiologists use to read those images have quietly advanced to keep up with the acquisition technology. Over the past several years, display advances have been made in lighting, screen size, color, and calibration, according to ACR experts and radiology display manufacturers.

Khan Siddiqui, MD, chair of the ACR’s information technology and informatics committee, says displays help make images sharper, which raises the question of how much difference this makes. Are radiologists, armed with higher resolutions and better lit monitors, able to see areas of concern previously not visible on studies? Does the ability to better visualize such areas raise unnecessary alarm or lead to improved, more accurate diagnoses and treatments? That could be the new debate as acquisition and display technologies advance. Meanwhile, here’s a look at what happened in recent years to improve the quality of the screens and the images they display.

Display Technology Changes
When you are looking at an image, the monitor’s backlighting should be consistent so that it’s equally bright, whether you are looking at the middle or the edges of the display, Siddiqui says. Backlight technology has helped to address this issue and ensure image consistency.

Like television monitors, radiology displays originally used a cathode ray tube design. Today, most monitors that radiologists use for reading studies are liquid crystal displays (LCDs), which offer several advantages. For starters, LCDs are thinner, allowing displays to be slimmer. In addition, older LCDs use a standard compact fluorescent bulb to provide the backlighting needed to illuminate the screen; newer LCDs use light-emitting diodes (LEDs) as the backlight source, says Tara McCall, sales and marketing manager for Double Black Imaging. The LEDs replace cold cathode fluorescent lamps (CCFLs) as the light source, utilizing near identical LCD technology, but LED backlighting provides a mercury-free source. Studies show LED contains other dangerous metals but doesn’t carry the health and environmental risk of mercury, McCall says. Furthermore, LED LCD life expectancy is specified higher than CCFL LCD. LEDs also can dim black in a region providing improved contrast over traditional CCFL, she says.

“CCFLs burn out quicker and have a natural affinity to fluctuate,” confirms Joey Sanchez, brand development manager at EIZO, which in 2012 became the first in the industry to have its entire diagnostic monitor lineup utilize LED backlights. LED backlit monitors also are more energy efficient; when EIZO tested comparable monitors at their recommended brightness, it found that the LED backlit monitors used about 25% less energy than those lit with conventional CCFLs and had about twice the longevity.

Siddiqui notes that the ambient lighting in the room can affect how well you can see the screen, but this is a separate issue.

Screen Size
Pixel pitch, defined as the distance from the center of one pixel to the center of the next, measured in millimeters, has become the new buzz in displays. Pixel pitch correlates with the display’s resolution; the smaller the pixel pitch, the closer the observer can be to the display and still have vivid resolution. “Small pixel pitch goes hand in hand with higher luminance, which is why we offer displays with calibrated brightness up to 1000 cd/m2, the same brightness as a film on a lightbox,” says Albert Xthona, product manager for Barco, a company that designs and develops visualization solutions for the health care industry.

The ACR recommends a display with a pixel pitch of 0.200 mm and not larger than 0.210 mm for diagnostic interpretation. “This equates to one of our 3-MP or 6-MP medical displays,” McCall says. The FDA, which approves digital mammography monitors and enforces the Mammography Quality Standards Act, requires that mammography be read on 5-MP monitors. That’s the only case where the number of pixels is dictated, she notes.

Until recently, 3-MP monitors were considered high end, says James Lupino, business development manager for USEI, a supplier of Totoku-brand diagnostic monitors. Today, 3 MP is “pretty much the standard base monitor that most radiologists are using for diagnostics,” Lupino says. These monitors are increasingly common, and the price differential between 2 MP and 3 MP is closing. “That’s why we don’t see a lot of business with 2 MP anymore,” he explains.

Radiologists favor 3-MP monitors not only for their diagnostic workstations, but also for their color displays, Lupino says. Previously, color monitors couldn’t offer radiologists the brightness desired for viewing grayscale images, so grayscale monitors were mainstream. That began to change about a decade ago when Totoku introduced high-brightness (more than 350 nits) color 3-MP monitors to Kodak Health. Color now is the mainstream, Lupino says, with the exception of mammography, which primarily uses 5-MP grayscale monitors.

Many radiologists equip their workstations with dual monitors side by side; this enables multiple views of one study or comparison of images from different studies. “You want those two monitors to be as closely matched as possible so you can tell subtle differences when making a diagnosis,” Sanchez says. An optional third monitor, though not necessarily diagnostic, can display the patient’s data.
One 6-MP monitor can replace two 3-MP monitors side by side; similarly, a 4 MP can replace dual 2-MP monitors or a 10 MP can replace dual 5-MP monitors. The arrangement essentially puts two monitors in one unit; a 6-MP monitor is essentially two 3-MP monitors side by side with no bezel separating them. The advantage is “you’re able to control how the image looks across the entire screen a lot better,” Sanchez says. “You no longer have to compare two entirely different monitors. You rely on one monitor to provide both images.”

Some radiologists find that one large display surface is preferable to having two smaller surfaces, says Xthona, whose company, Barco, offers several such monitors. “There used to be concerns about viewing angles if you have one display that is flat and not much wrapping around. But the viewing angle of modern displays is much better; now it doesn’t matter if part of the display is straight in front of you and part is a little bit at an angle,” he says.

The larger screen size also allows radiologists to read larger images without having to zoom or pan as much to see details, Xthona says. It has a built-in efficiency, which can be important in today’s environment where radiologists, like everyone else, must do more with less, he says.

Lupino believes adoption of 8-MP and 10-MP monitors will be slow until their price points decrease; as with all new technology, it will happen eventually, he says. However, Xthona notes that a 6-MP or 10-MP monitor makes economic sense because it means purchasing one monitor, not two 3 MPs or two 5 MPs.

Another innovation from Totoku is the first FDA-approved use of a 3-MP grayscale monitor with independent subpixel drive technology for mammography, Lupino says. Because grayscale monitors are essentially color monitors absent the color filters, each pixel actually consists of 3 subpixels that can be independently driven. With Totoku’s independent subpixel drive technology, a 3-MP grayscale monitor becomes a 9 mega-subpixel monitor, and, he says, with the compatible viewing software, the radiologist can use the lower-cost (about $2K less) 3-MP grayscale monitor for mammography. “With budgets and cost controls becoming more important, we see this as a growing trend in the mammography field,” he says.

Calibration
All medical displays must be calibrated to the DICOM 3.14 standard. Additionally, ACR recommendations have been adopted as industry standards. The objective is to ensure images are perceptually linearized. Gray levels must be sufficiently discernible to ensure no loss of diagnostic information. The 5% level should be as visible as the 95% level, flat grayscale areas are unacceptable, and the gray scale response must be consistent on all monitors, McCall says.

The ACR recommends each diagnostic monitor be set to at least 350 cd/m2 for diagnostic workstations with a black level of 1.0 cd/m2. For mammography, the recommendation is 420 cd/m2 with a black level of 1.2 cd/m2. The calibration process should involve setting the white and black levels to achieve consistent brightness and contrast ratio among multimonitor workstations and across the enterprise, McCall explains.

The way monitors are calibrated also has improved in recent years. Much of the improvement grew out of necessity, Sanchez says. Today, monitors can be calibrated remotely. “That means one administrator can calibrate all the monitors in his environment without having to go out to all their facilities,” he says. As facilities can be long distance apart and utilize numerous monitors, not having to visit each saves time and money.

Double Black Imaging has shipped autocalibrating displays since 2006 and continues to develop its software. “Displays designed to provide true autocalibration with a bundled calibration and reporting software suite help the support team by providing tools that proactively ensure enterprisewide stability, reporting, and compliance. We are the first company to include our Web-based calibration suite with our displays to completely automate this process,” McCall says.

EIZO monitors have a calibration sensor integrated into the front bezel of the monitor. “Whenever you need to do a calibration, it pops out,” Sanchez says. “It’s only visible during calibration, so it is unobtrusive.” All EIZO monitors also come with quality control software. The administrator can see when the calibrations were completed and project the monitor’s life expectancy. “So you’ll know if in a few months, you have to replace your mammography workstation as opposed to waiting for it to fail,” he says. In the past, radiology departments would have redundant monitors on hand in case a monitor failed. “This allows them to buy only what they need and to be able to better plan and budget for replacements,” he says.
Barco’s monitors also have medical calibration and quality assurance software, Xthona notes; its calibration and quality assurance is performed online and can be reviewed remotely from any site at all times.

“There is a trend in health care toward adding more equipment yet decreasing the size of the staff,” Xthona says. “When health systems have fewer IT people and fewer PACS administrators, having a way to ensure the quality of the monitors without sending people to the sites becomes increasingly important.” Also “when staff is reduced, there’s no one to send if a problem with a monitor arises. It’s better if the IT staff can address it remotely,” he says.

Totoku monitors also come with remote calibration and quality assurance software that provides information to the administrator for planning on replacements, the company indicates.

The Future
The change from CCFL to LED has been exciting, but it’s nothing compared to organic LED (OLED) technology, McCall says.

OLED contains organic carbon within the emissive layer of the panel. This light-producing layer is self-illuminating, thus requiring no backlighting. This results in a thinner, lighter panel compared with existing or past technologies. OLED has the ability to dim the image at the pixel level vs. a region of the image. “Higher brightness, better contrast, larger screens, and a wider, more vivid color palette are some of the benefits that will be experienced. But they are not here yet due to low yield and high-cost challenges,” McCall notes.

All monitor providers are looking to put more smarts into the monitor, Lupino says. “The idea is so that you can connect to the cloud easier. There’s quite a bit of discussion and thoughts about placing computers in the monitors.” Embedding computers in the monitors would add functionality to them, he explains. “That might be coming down the road.”

Power-saving features also are coming on strong, Lupino says. With an eye on costs, some users want monitors that shut down or go into sleep mode when not in use. “It also helps to extend the life of the monitors,” he says. OLED monitors would provide much greater power savings because of the way they operate—each pixel emits light independently without the big losses LCDs incur due to color filters and polarizers. However, the cost of OLED is still prohibitively high. That cost combined with continued advances in LCDs, such as the use of quantum dots to improve color of LCD comparable to that of OLED, means OLED faces several hurdles to becoming a serious challenger to LCD in the medical imaging field, Lupino says.

EIZO is working on introducing more single monitors that can suit all modalities, Sanchez says. “A multimodality monitor can break up the display into several configurations and optimize each window and resolution for what you’re reading whether it’s CT, MR, or X-ray.” Separate monitors were once the standard; being able to use one monitor for all reads is more efficient. “The monitor is smart enough to distinguish grayscale from color and ensures that all images are accurately displayed,” Sanchez says. These types of workstations provide maximum efficiency, he says, “and eliminate the time you spend wandering the halls.”

— Beth W. Orenstein is a freelance medical writer based in Northampton, Pennsylvania. She is a frequent contributor to Radiology Today.