Display Calibration Made Easy

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Softcopy viewing of medical images require that the display tools perform day in, day out at an optimum level, and not just in radiology, but throughout the entire healthcare enterprise where primary reading stations are needed. Quality control fundamentally improves image quality and the consistency in which images are displayed. To be optimized, QC programs must be non-intrusive to radiologists, manageable for the QA administrator to carry out, consistent throughout the enterprise, and of course, cost-effective. Automatic and remote monitoring tools are making this possible, in addition to increasing productivity gains and streamlining QC programs.

The University of Pittsburgh Medical Center, which is on its second-generation PACS, has 400 primary reading workstations installed throughout the integrated healthcare system's multi-center campus. Prior to the availability of automatic and remote calibration tools, two IT personnel manually performed QA (quality assurance) on each display to determine if it was compliant with DICOM (digital imaging and communications in medicine) part 14 grayscale standard display function (GSDF). Traveling to more than 17 hospitals, evaluating each workstation—which could take up to 30 minutes—and coordinating a time that was non-intrusive to radiologist workflow proved to be almost impossible.

This list of problems is exactly why quality control (QC) programs are often neglected at many hospitals, especially in lieu of large PACS deployments that consume a lot of resources. But without QC, image quality of the display can degrade over time, opening up the possibility of improper diagnosis or interpretation of a softcopy image.

With advancements in calibration software, QC does not have to be as ominous as once perceived. A well-planned and executed QC program with the help of emerging calibration tools can alleviate the arduous nature of display calibration, lower administrative costs and ensure excellent image quality for interpreting physicians. UPMC realized this as it moved to the next wave in display calibration - remote monitoring.

The elements

As radiologists make life-critical decisions on medical imaging displays - be it LCD-based (liquid crystal display) or CRT (cathode rode tube) - QA checks and re-calibration is fundamental to ensure optimal image viewing.

Research attests that LCD-based displays are typically more stable and require less frequent calibration than their CRT counterparts, making them the standard of choice for new PACS rollouts and monitor replacements. Despite their advantages, an LCD's brightness will degrade over time. The most influencing parameter aside from lighting conditions is backlight degradation. Brightness decreases as the phosphors used in the fluorescent backlights of LCDs age. If the backlight is not monitored and re-calibrated, it could fail to be DICOM-compliant over time.

"DICOM calibration is a fundamental requirement for displays used in medical imaging," says Matt Harris, vice president, marketing and corporate development for Planar Systems Inc. "The reason why? The DICOM curve is really meant to represent how the human eye perceives shades of gray. The human eye can better perceive differences at low gray levels than at high gray levels. So the DICOM calibration function, used in LCD displays, is created to mimic the sensitivity of the human eye."

Harris explains that the typical response curve of an LCD looks nothing like that of a DICOM curve. "What DICOM calibration really does is change the response curve of an LCD into that of a DICOM curve, and it allows a much higher degree of gray level separation at low gray levels," he says. In a healthcare enterprise and distributed PACS environment, this ensures that softcopy images look the same when viewed on different workstations at different times.

LCD calibration

There are three modes of display calibration for flat panels, Harris explains. The first - factory calibration - ensures that the graphic board has been adjusted prior to shipment so that the display renders DICOM-calibrated images. An acceptance test upon arrival of the new monitor must take place to confirm the display is DICOM compliant.

The second way to calibrate uses an external photometer (sometimes referred to as a puck) to reset the display to the DICOM GSDF curve. "From time to time, the medical imaging display should be manually calibrated," says Harris. "The external photometer works with calibration software