On Display: Monitors Show Their True Colors

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Film on a lightbox or a digital image on a monitor - while the purpose is the same, the technology behind each is oh so different. The bottom line remains that the radiologist wants to know that the images - analog or digital - are of optimal diagnostic quality, as do specialists or referring physicians viewing them.

The need for accuracy in the digital environment is pulling the display market away from traditional cathode ray tube (CRT) technology in favor of liquid crystal display (LCD) technology. In a study presented at this year's SCAR (Society of Computer Applications in Radiology) conference in Boston, researchers concluded that 3-megapixel (MP) LCDs are equivalent to 5MP CRTs in their ability to display lung nodules.

Proof that radiologists can see the same diagnostic information on both devices has helped fuel sales of medical-grade flat panels throughout the radiology community. While the transition is already underway in larger institutions, any healthcare facility in the market for new monitors must understand the differences between CRTs and LCDs to assure image consistency throughout and across the enterprise.


A year ago, Henry Ford Health System in Detroit replaced their disparate CRTs with digital flat-panel displays.

The purchase included 82 3MP, dual-head, monochrome LCDs from National Display Systems (NDS) for primary diagnosis, 24 2MP Sharp flat-panel color monitors for ultrasound applications and 680 19-inch Dell 1900 FP desk-top monitors for referring physicians and technologists.

"LCD monitors do now seem to be the preferred devices," says Michael J. Flynn, Ph.D., senior staff physicist at the hospital. "I think for many people the infusion of flat-panel monitors into the field, particularly for the diagnostic images in 3MP and 5MP monochrome monitors, has grown extremely rapidly."

"Two years ago, there really were minimal devices in the field and much concern that perhaps LCDs would not perform adequately. Now they have demonstrated that their image quality is better and their stability and service history is quite favorable. All of the experience we have had [with LCD monitors] is that they are extremely stable. Therefore, we have ramped down the frequency for calibrating these systems to an annual check performed by a staff within the physics department," explains Flynn.


Radiology images must be DICOM compliant - that is, they meet the grayscale display function (DICOM Part 14), making calibration mandatory. Guidelines, such as those devised by the American College of Radiology (digital image data management) and the American Association of Physicists in Medicine's Task Group 18 (TG18), assist in devising an ample strategy.

DICOM part 14 deals with optimizing grayscale to match human visual perception (www.acr.org), while TG18 provides a series of techniques for measuring characteristics such as luminance, uniformity, resolution, noise, veiling and glare (http://deckard.mc.duke.edu).

But the permeation of LCDs into the radiology environment has changed the rules of proper monitor regulation. LCDs are digital, low-powered devices with built-in sensors that continually take readings of the brightness and feed the information back to the panel's electronics, thereby stabilizing the brightness over time. While the monitors do require calibration, it's more of a hands-free, internal calibration; using technology on the backlight and on the front of the screen. Companies also supply their monitors with sophisticated calibration software and controller cards - boiling maintenance down to a minimum.

CRTs on the other hand, are notorious for drifting - requiring quarterly manual calibration checks with a photometer. Big, bulky devices that can introduce distortions as a result of their curved surface, their LCD counterparts are more compact, take up less desk real estate and last approximately 25,000 to 30,000 hours.

"LCDs tend to be brighter, last longer, put out less electromagnetic radiation, run cooler and are more stable. We believe the total cost of ownership of LCDs is less, also," says Eliot Siegel, M.D., chief of imaging at the Baltimore VA Medical Center. "We have switched from the standard 5MP CRTs with 4MP video cards to 3MP active matrix medical-grade LCDs" continues Siegel.


If the LCDs are being used for diagnosis, they are most likely what manufacturers have coined "medical grade" monitors.
"Consumer displays typically max out by 1600 x 1200, so they go up to about 2MP and medical-grade starts out at usually 2MP - because they are monochrome and brighter - and go up to 3 and 5 mega-pixel versions. Medical grade monitors offer higher resolution and brightness," says David Hirschorn, M.D., research fellow at Massachusetts General Hospital and director of informatics at Staten Island University Hospital.

"The medical-grade vs. consumer-grade LCD is a hot area," continues Hirschorn. "A typical medical-grade display today is 3MP grayscale - and they are grayscale because it makes them brighter."

Black and white digital x-rays require undisputable image quality and accurate grayscale rendering that high-end, medical-grade LCDs offer. While computed radiography (CR) and digital radiography (DR) require higher resolution monitors, MR, cardiac, ultrasound and nuclear medicine on the other hand, can be read on lower resolution monitors, making the quest to purchase the right ones even trickier.

The ACR has put its foot down in a couple instances, such as a 50 foot lambert minimum and 5MP minimum for digital mammography images. Eizo Nanao Corp., for example, offers a 5MP 21.3-inch LCD to its RadiForce line, G51. The system requires a dedicated video card, is available in both clearbase and bluebase versions with 2048 x 2560 resolution, and contains the company's calibration software called Dr. Kal.

Another high-end monitor recently introduced as a primary diagnostic reading tool is Data Ray Corp.'s ADCal 11 3MP LCD with more than 7,000 shades of gray and self-calibration software. The monochrome flat panel can detect 7141 (12.8 bit) gray shades for static image mode and 1786 (10.8 bit) for cinema mode.


The companies that supply medical grade LCDs for diagnosis offer a mix of mega-pixel, grayscale monitors; since specifications such as brightness, contrast ratio and viewing angle are typically the same, companies differentiate themselves with calibration techniques, the tint of the backlight, warranty, service, aesthetic design and cost.

But don't base your LCD purchase on past CRT experience, says Mark Lutvak, sales and marketing manager of monitor provider Advan International Corp.

"With PACS, things like brightness, contrast ratio and response time of the panel are important, not just resolution. If it is a cath lab application, brightness and response time of the display are important, not resolution at all," explains Lutvak.

Advan's generation of 20.1-inch color and grayscale (AGM/AMM 20TIG, formerly 20TDG) LCD flat-panel displays are geared toward medical imaging applications such as PACS, DR and cardiology.

If the monitors are not for primary diagnosis and rather intended for wide-area distribution, a more affordable, lower resolution monitor is suitable. Higher-end LCDs are expensive: dual-head 5MP configurations range in cost from $28,000 to $40,000 and 3MP range from $17,000 to $24,000. Lower resolution monitors cost a little less: 2MP dual-head displays range from $12,000 to $15,000, with a 1MP ranging from $8,000 to $10,000.

Lower resolution monitors for referral, office use, review stations and teleradiology are in high demand as the Internet has allowed images to travel beyond the walls of the radiology department. Planar recently announced Adara, a family of referral-quality grayscale displays calibrated to the DICOM standard and intended for general medical viewing as an addition to its Dome lineup. Double Black Imaging (DBI) offers the IF1801A, a 1.3MP, 18.1-inch, high-bright monochrome LCD to replace most existing review or modality CRT monitors. NDS has released PrimeVue, a 19-inch DICOM grayscale compliant color flat-panel display to be used as a primary reviewing station.

DBI, of Westminster Co., launched in July, sells a family of DICOM 3.14 Wide LCDs that are color or monochrome, 1 to 5 mega-pixels with pre-set and pre-calibrated brightness levels, certified to the medical safety standard, UL2601-01.

In addition to their new remote calibration software and IF1801A 1.3MP display, DBI is launching a new line of 2MP, 3MP and 5MP self-calibrating LCDs that are equipped with an electronic sensor that emerges from the bezel and retracts when calibration is complete.

On the list of new contenders, NEC-Mitsubishi Electronics Display of America Inc., which currently sells a line of Professional "80" Series monitors for medical office information systems, will release a new line of diagnostic displays in summer 2004. Based in Itasca, Ill., the company will introduce its MultiSync MD Series, a 21.3" color 2MP and a 21.3" grayscale 3MP medically certified display. Soon after their release, the company also has revealed plans to sell a 21.3-inch color 3MP display.


So how long will a display display? Hirschorn speculates that even though LCDs last far longer than CRTs, it may be possible to eventually replace the backlight in the digital displays. "LCDs should probably last about 3 to 4 years," explains Hirschorn. "Even then, theoretically, the backlight can be replaced. The panel itself does not degrade, it's just the "light bulb" in the back that does, which can most likely be replaced for about $700."

A slow loss of efficiency is inevitable as the phosphors used in the lamps to generate visual light deteriorate over time. Companies are addressing this deteriorate, such as Barco's new backlight technology, Duralight. An option on the company's Coronis 3MP medical display system, Barco says DuraLight extends the lifetime of the LCD without increasing power consumption or compromising visual performance.

Developed for a PACS environment, Barco's Coronis line consists of 1, 2, 3 and 5 mega-pixel displays bundled with a high-speed, 10-bit display controller and MediCal QA management software. Displaying 1024 shades of gray, the Coronis monitors are equipped with an I-Guard sensor on the front of the screen that monitors and stabilizes the output of the backlight.


LCDs have eliminated many of the problems associated with CRTs: space, heat, geometry, cost of ownership, and lifetime. However, there are some limitations that buyers should be aware of in the advent of their monitor change.

"The first consideration of LCDs is their viewing angle," says Elizabeth Krupinski, Ph.D., assistant professor of radiology at the University of Arizona. "When viewing on-axis with LCDs, everything is fine, but if you move off-axis, the luminance and the perceptions of the luminance change. Many companies are starting to deal with this and get better, but for most LCDs, this is a consideration."

Many displays are configured for use with one specific display controller, so don't just settle for aesthetic attraction. "The display that are 'bundles' are married to specific graphic boards," says Gerry McGinley, business unit manager of Richardson Electronics.


As more modalities produce images that require color, dedicated color LCDs - both medical and consumer - will find their way into reading environments.

"There are some 2MP 20-inch consumer monitors that are very nice. We now use them for ultrasound and are looking to put time in our surgical unit," says Henry Ford's Flynn. "We are beginning to see 3.5MP, and in one case, a 9MP LCD off-the-shelf color monitor coming on the market."

Radiologists are already reading 3D images on 2D displays, but in the future, expect to see more 3D displays in use. Siemens Display Technologies announced a new 18-inch medical grade 3D display this month at RSNA. The multi-user display, Extreme 3D display (X3D), was created by a cooperative effort of Siemens Automation and Drives and 3D developer x3D Technologies Corp. of New York City.

Finally, LCDs are growing as large in size as they are in popularity. Flat-panel LCDs measuring 37-inches, have found homes in many operating rooms and radiology reading rooms already. Adopting these "big guys" as part of their display family is just another way hospitals are smoothing their transition to soft-copy reading.

Easier Calibration

Barco and Planar made essential monitor calibration a lot easier this spring when they each launched enterprise management software for LCDs; PIN (product intelligence) and Cxtra, respectively. The products essentially eliminate the frustration associated with frequent manual calibration, allowing each display to be monitored from a central location.

Double Black Imaging released its Remote Administrative software at RSNA, which, like PIN and Cxtra, alerts a specified location if a display requires service or adjustment. Image Systems Corp. of Minnetonka, Minn., debuted Calibration Feedback System (CFS) at RSNA as well. CFS is a local and network-addressable display calibration system for use on the company's 2MP, 3MP and 5MP grayscale AMLCD displays.