Alternative flat-panel technology tackles display issue

February 19, 2001

Monitor performance may be the weak link in the digital PACS loop, but a solution could be in the offing. A "light valve" technology called suspended-particle display (SPD) offers workstation characteristics radiologists may find attractive. Not only

Monitor performance may be the weak link in the digital PACS loop, but a solution could be in the offing. A "light valve" technology called suspended-particle display (SPD) offers workstation characteristics radiologists may find attractive.

Not only are bright, high-contrast digital displays possible, according to the inventor, physicist Robert Saxe, but flat-panel SPD monitors can be dimmed or brightened with electronic precision to suit individual needs. A rheostat-like device allows an infinite range of adjustment between completely dark and completely clear.

"The advantage for any SPD flat-panel display, compared with, say, liquid crystal display (LCD) technology, is the screen is much brighter and easier to read because the contrast ratio is much greater," said Michael LaPointe, director of architecture and information displays at license holder Research Frontiers, in Woodbury, NY.

Contrast ratios for SPD devices, at 850:1, are two to three times higher than LCD screens, at 250:1, according to LaPoint. By comparison, the best Palm Pilots have a contrast ratio of 15:1, which is why they're so difficult to see in an outdoor setting. LCD displays are used on laptops.

Another plus of SPD monitors is their ability to allow viewing from wider angles, LaPointe said. A wider viewing angle doesn't mean image degradation when looking slightly from the side as it does with a laptop computer - an advantage in a teaching environment.

SPD devices could also cost less than traditional monitor technologies, due to simplified construction requirements.

"SPD devices are constructed in a manner similar to an LCD, but rather than pouring in a liquid crystal material you slide in a sheet of SPD film material," LaPointe said. "With SPD, you don't need alignment layers and sheet polarizers like you do with liquid crystals. The result is cheaper cost and brighter displays because polarizers and alignment layers cut down on light throughput."

Workstation manufacturers remain cautious about SPD's future in radiology.

"SPD might be a possible technology for low information content displays," said David Sorensen, vice president of operations for Image Systems Corporation, a Minnetonka, MN, maker of custom high-resolution monitors. "I don't know if it really lends itself to the high resolution required in radiology or how well it will be able to control critical gray scales."

Nevertheless, the technology might still be useful as an over-the-surface contrast-enhancing treatment to a CRT or LCD, according to Sorensen.

"Instead of using an additional contrast-enhancing glass panel or thin film, which has one set level of transmissivity, this technology could be used to change the transmissivity of the front panel to meet changing ambient lighting conditions and thus give optimum contrast," he said.