Direct monitor purchases save money but require more care

July 1, 2007

When PACS were first introduced, the vendor supplied the whole system, from the back-end servers to the front-end diagnostic workstations. Over time, the buyers of these systems realized that none of these PACS vendors actually manufactured the computers and monitors; they just resold them, often at huge markups.

When PACS were first introduced, the vendor supplied the whole system, from the back-end servers to the front-end diagnostic workstations. Over time, the buyers of these systems realized that none of these PACS vendors actually manufactured the computers and monitors; they just resold them, often at huge markups.

Many hospitals and imaging centers today choose to buy PACS computers themselves and are comfortable integrating them into their networks. But when it comes to monitors, that's a different story, because it's primarily the monitors that distinguish the hardware of a PACS workstation from that of an ordinary computer. They usually make up the bulk of the cost as well.

Fortunately, like the computers and storage components of PACS, monitors have become commoditized. This means that they are cheaper and easier to obtain. Radiology departments can buy them directly from distributors-and in some cases manufacturers-instead of from the PACS vendor. Along with this new opportunity, however, comes the burden of deciding what to buy and of maintaining it.

The first step in deciding what to buy involves choosing between monitors made especially for the medical imaging market and those made for the general consumer market.

During the first decade of commercial PACS availability, no such choice existed. Although generic computers, storage, and networks generally sufficed for medical imaging, the consumer displays of that time did not. The color cathode ray tubes (CRTs) of the last decade had many limitations that made them unsuitable for radiologic image display. One of the biggest was that they simply weren't bright enough to display enough shades of gray for diagnostic interpretation of a chest x-ray. This gave rise to a whole new industry of medical-grade monitors, designed specifically for medical imaging display.

It began with the 1-megapixel gray-scale CRT and ultimately progressed to the 3-MP gray-scale liquid crystal display of today. These displays were made gray scale not because of any inherent problem with color but to enable increased brightness of display. In other words, they simply couldn't make a color display with the same brightness as a gray-scale display. Since 2005 this is no longer the case.

But the psychology of buying monitors specifically designed for medical image display is deeply ingrained, and these monitors still do offer some distinct advantages over general consumer displays, albeit at a much steeper price. Furthermore, only a few models of consumer displays are suitable for medical imaging, and their setup and management is a new experience for most radiology departments.

Typical 3-MP gray-scale displays have features not currently found in their consumer counterparts. First, they have a brightness stability control, which is analogous to a thermostat. This means that if they are set to output 500 cd/m2 (candelas per square meter), they will adjust the voltage and send enough power to the backlight of the display, based on the readings of a built-in light sensor, to produce that brightness. This compensation acts both in the short term, during the warm-up period of the fluorescent lamps when the monitor is first turned on at the beginning of the day, and in the long term, as the lamp output naturally decays over the years.

Second, these displays allow a tight calibration to the DICOM Part 14 Grayscale Display Function. Like a musical instrument, they can be very finely tuned. The displays are usually calibrated at the factory, and, provided they can keep their light output constant, they can often maintain their calibration for long periods of time.

But a pair of these displays typically costs about $12,000, and they cannot display color.

In 2005, the consumer display market debuted a new offering, a 2.3-MP color display with a light output of about 450 cd/m2. It lacks brightness stability control, and its backlight does decay significantly over time, such that it remains suitable for radiography for only about 18 months rather than the five years typical for medical gray-scale displays. However, at roughly one-tenth the price, they are much cheaper to use and provide color capability, which is important for viewing color Doppler ultrasound, nuclear medicine images, functional MRI, 3D, and CAD. What's more, when they reach the end of their useful life for radiography, there are options. They can be relegated to use as viewers for such nonradiographic images as CT, MR, and ultrasound, none of which requires the same high brightness as radiography. Or they can be repurposed as nonimaging monitors for work list, dictation, or even just plain non-PACS desktop displays, where they will remain useful for many more years.

To use these monitors for imaging, however, they must be calibrated, and this requires considerably more effort than is needed for their medically marketed counterparts. And their calibration cannot be as fine, though many would argue that doesn't matter, and to most radiologists the difference is barely noticeable.

MEDICAL DISPLAYS

Displays designed for medical imaging usually come with a controller board that fits into a slot of the computer. The slot standard for older computers is PCI; for newer computers it's PCI express. But most newer computers come with both types of slot. After physically installing the controller card into the computer, digital visual interface (DVI) cables are typically used to connect the monitors to the controller card.

Next comes the software. Drivers are loaded onto the operating system of the computer to allow it to properly utilize the features of the controller and the displays. At this point, the displays are set to their proper resolution and orientation. The computer desktop is arranged to reflect the physical location of the displays so that the cursor transitions from one monitor to the next smoothly as it moves across the screens.

Then the calibration software is loaded and run. It should allow the computer to check the light output and calibration conformance (the fine tuning) of each display and should record those results in a log. Such checks should be run periodically-quarterly or biannually. If the check fails or if it cannot be run, then technical support should be contacted. The monitor may have to be replaced.

What too many radiology departments do not realize is that these checks will not run on their own; they must be set to do so. And even then the results need to be looked at on a regular basis to recognize and address any problems the calibration conformance checks detect. Too often, both the radiology department and the PACS vendor assume that these expensive displays take care of themselves when in fact they do not. They, too, need care and maintenance, albeit far less than consumer displays.

CONSUMER DISPLAYS

The setup process is very similar to that of medically marketed displays, with a few key differences. While the display literature may give a list of compatible graphics controllers (aka video cards), none comes with the display. It's up to the buyer to buy one separately. For the 1920 x 1200-pixel displays, the controller that we prefer is the nVidia NVS 440 because it can drive up to four monitors, which is how many we typically have on a PACS workstation. We also buy the DVI Y-splitter cables for the card to send each monitor a DVI signal instead of an analog video graphics array (VGA) signal. VGA signals are subject to electromagnetic interference, which is frequently encountered in hospitals and near imaging equipment.

We then usually attach two simple 19-inch flat-panel displays, for work list and dictation functionality, and two 24-inch 1920 x 1200-pixel displays rotated to portrait orientation. For maximum light output, the displays must be set to maximum resolution, maximum brightness, and the "user preset" color setting. Consumer displays have no built-in photometer, so we then calibrate the displays using VeriLUM from Image Smiths, which requires holding a photometer (which looks like a hockey puck) over each screen for about four minutes. The white level is checked to make sure it is within an acceptable range (400 to 500 cd/m2), and the calibration conformance is checked as well, to make sure it is within an acceptable range ( < 0.075 JND RMSE [just noticeable difference root mean square error]).

Calibration checks as described need to be run quarterly or biannually. A major difference between consumer and medically marketed displays is that the luminance will drop over time with consumer displays. This may have an effect on the calibration conformance, which requires recalibration and, eventually, monitor replacement.

Using these high-brightness consumer displays for PACS is also, to some degree, uncharted territory for the manufacturers. They are not used to customers complaining that they measured the luminance of a display with a photometer and found it to be too low too quickly. Their warranties do not directly address the issue. Though the vendors we have dealt with have been accommodating thus far, we know that they cannot keep exchanging monitors for us endlessly as their backlights decay. Nonetheless, we know that even if a display becomes too dim for radiography and is not eligible for warranty exchange, it can still be repurposed as described above and retain a significant percentage of its value that way.

CONCLUSION

There is no question that medically marketed displays are optimized for display of radiography and many of the other modalities. While their care and maintenance is considerably simpler than that of consumer displays, there is a burden to maintaining them that is too often ignored by radiology departments and vendors alike, usually due to lack of knowledge. These displays, too, need to be checked periodically.

The use of consumer displays for PACS requires more knowledge when selecting and setting up monitors and video cards, and it takes more work to calibrate and to check that calibration periodically. It will also require more frequent monitor replacement. It is up to the hospital or imaging facility to decide if those trade-offs are worth the color benefits and the drastically lower price.

Dr. Hirschorn is a research fellow in radiology informatics at Massachusetts General Hospital and Harvard Medical School, and director of radiology informatics at Staten Island University Hospital.