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