LCDs & CRTs: Passing the Image Baton

Not so long ago, film was king, and the lightbox was the display technology of choice. Then, the introduction of digital imaging modalities and picture archiving and communication systems (PACS) started many imaging centers and departments on the path toward filmless operation. Early filmless reading rooms were stocked with CRT monitors for image display. Although CRTs can be hot to operate and cumbersome to move, many radiologists grew to love them for price and image clarity properties.

Then came the introduction of the affordable LCD display. These flat-panel monitors gained early acceptance on many office desktops, hailed for their bright, nearly flicker-free displays and small footprints. But concerns about image quality for diagnostic accuracy held many radiologists back from the LCD love-fest. This is, however, beginning to change. Within the past two years, LCDs have come down lower in price and increased in image clarity, making them a viable choice for image viewing in a wide variety of settings.


Eliot Siegel is professor and vice chair of information systems in the department of radiology at the University of Maryland (Baltimore) and chief of radiology and nuclear medicine for the VA Maryland Healthcare System. He notes that, as one part of one of the first hospitals to go filmless, he has been using softcopy displays for some 11 years. He is currently working with a combination of CRTs and LCDs, and, as the need arises to replace the 5 megapixel CRTs, in come the 3 megapixel LCDs.

Obviously, the most important factor to consider when purchasing a display is confidence in diagnosis, and Siegel is confident that LCDs pass the test. "We did scientific investigations and documented the LCD is not a compromise in ability to diagnose," he says. He finds any minor differences between the 5 megapixel CRT and 3 megapixel LCD to be insignificant in daily use. "At the distances radiologists [sit] from the monitor, they can't tell the difference."

Early studies by Siegel and colleagues comparing radiologists' readings of images of lung nodules and a variety of musculoskeletal images indicate that LCD displays compare favorably with CRTs on matters of specificity, interpretation time, and radiologist's confidence on the read. (Fujifilm Medical Systems USA Inc. provided the PACS for the research study and some funding support.)

Three megapixels may not turn out to be the lower limit for LCD resolution. Siegel notes that he is "planning on doing a study with 1 to 2 megapixel LCDs, [to] look at the difference in radiologists'Ã?¢?Ã?¦ confidence in making diagnoses." The results of such investigations may ultimately indicate that lower resolution LCDs are still appropriate for diagnosis.

John Hart, a PACS administrator for Willamette Falls Hospital Diagnostic Imaging in Oregon City, Ore., also is finding strength in LCDs. He has overseen more than 40 PACS installations, and increasingly prefers LCDs to CRTs, especially in the OR or NICU.

Hart finds LCDs preferable for a wide variety of applications, even some that have traditionally been the last hold-outs for CRT. "We even do mammography under LCD," Hart says, noting that LCDs have only recently gained FDA approval for the display of mammograms. One of the hurdles has been display resolution. Mammography "requires higher resolution because so much more zoom is needed," he says. "We try to get LCDs that can do [the] 5K display required for mammography."

Not only are LCDs making inroads into mammography, Hart feels that there are certain situations in which LCDs are the only viable choice. "LCDs are a must in the OR," he says. Why? First is footprint size; "you want [your display] as small and compact as possible," he says. Second, he notes the need to maintain a cool operating room, a task that is made that much harder by the higher level of heat output from a CRT. Finally, "CRTs are well known for static [and] case leakage; you can't have [that] in the OR or NICU," he says.

This is not to say that everything about LCDs is a clear benefit over CRTs. "It is more difficult to calibrate LCDs," Hart explains. This is in part due to the composition of the screen. If you push on an LCD display, you will notice that the image will "flow" a bit as the screen depresses. CRTs, being a hard screen, are not subject to this "flow."


Once past the diagnostic confidence consideration, those considering a new display purchase should look to total cost of ownership when comparing LCDs and CRTs. In a presentation given by Siegel at SCAR 2003, he noted that "declining prices and increased performance have made AM-LCD monitors much more attractive candidates for use in PACS for both primary and secondary diagnoses." He also noted a trend in which LCDs were outselling CRTs for primary and non-primary interpretation.

In spite of higher (but declining) initial purchase price, Siegel believes that LCDs ultimately carry a lower total cost of ownership than CRTs. He has conducted studies and found that CRTs typically begin to experience drift and require replacement or recalibration in about 18 months, with a maximum lifespan of about 3 to 4 years. With LCDs, Siegel says, problems can often be remedied by simply replacing the backlight. Hart concurs with these estimates. He estimates CRTs to have a 3 year lifespan, while he expects LCDs to last for 7 years.

There are many other considerations relating to cost of ownership that go beyond simple cost of the unit. For one thing, Siegel says, "it takes a great deal of staff to check [CRTs] regularly" and ensure that they are properly calibrated. He explains that his facility makes use of Society of Motion Picture and Television Engineers (SMPTE) patterns stored on the PACS and available at every workstation for quality control. "CRT drifts out of focus more often," he says.

Cost of ownership also involves cost of operation. Siegel notes that LCDs use less power, a direct savings on the utilities bill. They also create less heat by about half, which means that air conditioners will need to work less hard to cool a room full of LCDs than one full of CRTs.


With all of the benefits of LCDs, are some users still choosing to purchase CRTs? Certainly. Some of it is a question of experience with one display type. "Some [just] like CRT better," says Hart. However, he has noticed that even these users comment that the LCD display "looks better."

And lower initial cost, of course, continues to sell CRTs. Even though Siegel opines that overall cost of ownership is higher.

Finally, Siegel believes that speed may be one of the last areas in which CRTs outstrip LCDs. Those with applications that require very fast movement may still wish to use CRTs, thanks to their faster refresh rate, he says.

Overall, opinion on LCDs versus CRTs can be summed up by the words of Kenneth Fetterly, medical physicist for the Mayo Clinic. "Current LCDs display images with equal or better quality when compared to CRTs. We expect that LCDs will be more stable over time than CRT displays were. We also expect that they will last longer, thus reducing our annual cost of ownership. [And] vendors have developed methods to calibrate LCDs well, allowing for good presentation of radiographic images, even on color LCDs." With these benefits, many installations are coming to the same conclusion that Fetterly has: "Where possible, we replace CRTs with LCDs when the CRTs fail."