Executive Forum

Medical Displays for Filmless Imaging

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Manoj Tyagi (USEI)

Displays play a very important role in the field of digital imaging – whether it is for any modality, such as CR, DR, ultrasound, PACS, mammo applications or patient monitoring, and whether it is used by the radiologist, clinical staff or in the operating room. Display and its quality are major concerns for everyone.

Seeing images at the display is almost the final step of digital imaging before storing it with changes. When display is so important, it's natural for the radiologist, PACS manager or information technology (IT) manager to be careful in the purchasing process. Most decisions are made between the three groups consisting of radiology, PACS and IT.

We have gone now so far that comparing LCD with cathode ray tube (CRT) is not so essential. LCD is en vogue and everybody wants LCD now. LCD technology is getting standardized and improving every year. Most color medical displays are available from 1.3 megapixel (mega), 2 mega and 3 mega. Grayscale medical displays are 1.3 mega, 2 mega, 3 mega and 5 mega. Medical displays have a calibration feature, automatic brightness control, DICOM conformance and FDA approvals.

Warranties

Initially, LCD came in the market with 12-month warranties only, and hospitals would purchase extended warranties because the technology was so new and they did not want any workstation to go down even for 24 hours. But now, even a five-year standard warranty with an LCD is not so uncommon. Displays are getting brighter and brighter, display manufacturers are stretching it to the limits. You can find a 2-mega gray LCD with 1,500 or 1,800 Cd/m2 and a color 3-mega for 400 to 1,000 Cd/m2.

Contrast ratio is getting better, too. However, you can operate an LCD only from 200 to 450 max for the better health of your eyes. Because you are not using the full power of a backlight, its life increases and lasts for a few more years. This is good news for users because the backlight is the most failing part of the LCD and needs to be repaired every two to five years, depending upon the usage and at what brightness you are using it for.

If you are using a grayscale LCD, make sure that you get the color-matched LCD from your vendors, because as no two apples are alike on the same tree, every grayscale panel is slightly different than the other panels, even if they are made by the same manufacturer. And radiologists do not like using different-looking panels. If you are using them as a quad head set, make sure to get them color-matched as a quad head set.

Beside of brightness, contrast ratio and speed, there is a race between various manufacturers to show more shades of gray. Displays could be 8- and 10-bit. Now you can buy grayscale LCDs with 3,000 or more shades of gray and 2,000 or more simultaneous shades of gray.

Many users have to make a tough decision when it comes to resolution. For diagnostic quality, it has to be 2 mega and above; for mammo, it is usually 5 mega and above. For regular PACS use, it is a decision between 2 and 3 mega. And that is a tough decision. There is no guideline for which pixel offering is the best or must be used.

However, few hospitals buy only 3 mega and few buy only 2 mega and some buy mix of both. It depends upon personal choice, PACS vendor recommendations, budget, etc. However, since LCD prices are currently on the decline, displays are more affordable. For example, 3 mega prices have gone down from $40K/set to less than $20K/set.

Calibration

Calibration of these LCDs is one of the most common concerns for tech teams at the hospitals, as it needs to be repeated quite often. In addition, the radiologists become frustrated about having to recalibrate frequently, and sometimes, they must calibrate as soon as the day after they initially calibrated.

Most vendors can now provide a remote performance check software, self-calibrating display or remote calibration displays. A remote performance check software can talk to each workstation from a central PC and give the PACS manager all of the information about all the workstations, their numbers of hours, calibration status, etc. With front-sensor, self-calibrating LCDs, personnel can check their DICOM conformance status 24/7.

However, even though remote calibration is a convenience, performing calibration the old way – first calibrating the outside sensor and then calibrating the LCD sensor for automatic brightness control – is still a very good and reliable method.

Color vs. Grayscale

Another very important development in the field of LCDs is to use a color LCD as a grayscale LCD. Few medical applications need grayscale LCDs and few applications, such as ultrasound, need color LCDs. So you need two types of LCDs to look at different types of images. Earlier color LCDs were not as bright as they are today and their contrast ratio was also not as good. But since we've overcome these obstacles, now a small percentage of users have started using color for grayscale LCDs.

But, again, this is a personal choice for the user. Some users who are using color for gray are very happy with the change. And, at the same time, few users just don't want to try this method; they want to continue to use grayscale.

Also, another very important point is that any color LCD could be used to display the grayscale images. But, depending upon the panel make, brightness and contrast ratio, the output quality of grayscale images may vary. Only some of the brightest panels should be used for the grayscale images. And users should see for themselves how they feel about this change.

The experience of using LCD also depends upon the speed and convenience of its response. It could also depend on the speed of the panel, whether it features a single link or dual link. A dual-link LCD would be fast in response. The performance the user gets can also be dependent on the graphics board. All new PCs nowadays come with a PCI Express high-speed slot and, also, a PCI slot.

Before buying an LCD, please check your hardware, including what kind of graphics board slot you have: PCI or PCI Express. PCI Express boards are usually high in speed and low in cost, but sometimes they may not support 8-bit settings, and some PACS software requires an 8-bit setting. Also, they may recommend a PCI board only.

Other Features

There are other types of LCDs out there for special applications, such as bedside patient monitoring and an LCD with S-video input capability with picture-in-picture features so you can look video and X-ray at the same time. These LCDs are needed for fluoroscopy, endoscopy, etc. Also, a few applications, such as CR, might need an LCD with a touch-panel.

Also, users should check about the U.S. FDA approvals of these LCDs; although LCD technology is getting better each year, it does not mean all brands provide the same level of stability of the electronics, backlight, failing pixels, calibration and DICOM conformance consistence. Also, check if the user must buy the expensive graphics boards from the vendors and ask whether 10-bit look-up tables are inside the LCD or graphics boards.

Find out whether the same graphics board can do the pivot function of the LCD, because most displays in the medical industry are used in portrait mode. And, inquire as to how frequently their displays needs to be calibrated because every model or brand may have different requirements and stability issues of retaining calibration.

Also, check with the vendor about the anti-glare protective filter, which may protect your costly panel from regular damages or scratches. Check if this protective filter is attached to the panel or detachable. In North America, medical displays bezel are usually gray in color, rather than white or other color. Finally, when using displays in a pair, you may want display with as thin bezel as possible.

However, the good news is that technology will get better and better in the coming days. Users will get more life expectancy and stable products. And displays will get more affordable every day.

—Manoj Tyagi is the global sales and marketing leader for U.S. EIectronics Inc., Minneapolis (www.usei.com). Questions and comments can be directed to editorial@rt-image.com.