QA in Medical Displays: Two Approaches

 Quality assurance (QA) of medical imaging displays is critical for accurate interpretation of digital images. When it comes to QA, there are as many protocols out there as there are healthcare facilities. They each uniquely tackle what method they want to employ, how often they should calibrate the displays and who is responsible for the process.  Along the way, they update methods and procedures to take advantage of new technological options.

Hands-on method

At Allina Healthcare in Minneapolis, Minn., a large system with 11 hospitals and 39 clinics, the clinical equipment services division, part of IT, is responsible for quality assurance and service of all medical displays and diagnostic imaging equipment. PACS is used at all of the hospitals and several of the clinics handling a terabyte of images every 12 to 16 days, says PACS Administrator Bruce Facile.

The prevalent display in use for imaging needs at Allina is Image Systems grayscale FP2080 3MP. Recently, when they upgraded to color in radiology and cardiology, they chose NEC’s 2190 UXi 2MP color systems.

The cornerstone of Allina’s QA protocol is the tried-and-true method of manual calibration. “Our viewpoint is that you actually need to be in front of the monitor to do a visible inspection as well as calibration,” says Facile. “We want to make sure the clinical equipment services people do a site survey of the monitors so we can look for white pixels, black pixels, scratches on the monitor, defects and all of the other pieces that you can’t do using network calibration software.”

QA is performed by imaging technical specialists and engineers such as Kevin Emerson. “You get baseline luminance and then you gamma-correct the luminance curve, so all four monitors almost all have an equal luminance curve. So if you pull up the same image on all four monitors, there is no difference to the human eye.”

Allina will soon be switching from the Verilum software and puck systems to Image Systems’ self-calibration feature—an onboard front sensor—to do a validation of DICOM and other tests. DICOM Part 3.14, Grayscale Standard Display Function, is one of the standards used by many hospitals to maintain and calibrate displays.  The Image Systems QA solution, Calibration Feedback System, measures conformance of the displays. The newest version has been upgraded to include color calibration and enhanced reporting features.

At this time, Allina is not planning to purchase network software to perform monitor calibration and remote testing. “We have confidence in the stability of our monitors,” says Emerson. “Every day a trained professional is viewing these monitors and making diagnoses. If there is a problem, it’s spotted.”

Going remote with calibration

At Delnor-Community Hospital in Geneva, Ill., a 128-bed hospital that is completely filmless and does approximately 109,000 radiology procedures annually, they rely on network calibration software for QA, says Brian Daily, PACS administrator.

The hospital uses Double Black Imaging’s black and white displays.  The typical workstation configuration is a pair of Double Blacks, IF 2103M (3 MP) or IP 2105M (5 MP) and a 19-inch or 20-inch color display from NEC, which is used primarily to view worklists. 

Delnor relies on Double Black’s network calibration software, LumiCal, for performance testing, calibration and maintenance. “The software resides on a server. You just need to put in all of the different monitor combinations with the serial numbers and tell it to go out at 2 a.m., or whenever you want it to, and it calibrates the systems for you,” says Daily. “We do it once a week.” 

The network management software which can run at any time, allows Daily to adjust luminance levels, create reports, run visual tests and sends automatic alerts if there is a failure with any display on the network, as well as calibrating locally or remotely.

Double Black’s calibration process is performed by several sensors on the displays. “On the 5 MP, the sensor is automatic, it’s stationary and always out; but in the 3 MPs, it motorizes out,” Daily says. The LCDs also come equipped with a backlight sensor for continuous luminance calibration. 

Daily wanted self-calibrating displays, but found that the term doesn’t necessarily mean the same for all vendors. To Daily, it means backlight and front light sensors, being able to calibrate brightness, adjust the black level, white level and contrast and the ability to retrieve reports.

“We wanted to have automatic calibration,” says Daily. “We found that some vendors said they did automatic calibration, but when we read the manual, it said if you really want to make sure it’s DICOM compliant, you have to do it manually with a puck.”

Daily says they were not in favor of manual calibration because it’s “very labor intensive, and as you can tell, we have a lot of monitors and you can’t really go in and stop a radiologist from working during the day.”

The remote calibration software also keeps a history and log of all DICOM calibration and conformance tests. It also has user-friendly graphics detailing gray-level luminance up to 256 individual points from black to white and contrast.

“The bottom line to me is ‘does it meet the DICOM conformance standard?’ If it’s self-calibrating, it should provide something that says whether it meets the standard,” says Daily. “The one thing that we like to specify is [DICOM] Part 3.14.”

Manual, remote or a combo

As the job of performance testing and maintenance of displays becomes larger and more time-consuming with further integration of PACS throughout the healthcare enterprise, many hospitals are moving toward self-calibrating displays and some type of network administration capability. Others believe that the benefits of local calibration and physical inspection cannot be discounted. The best QA program may be some combination of both. It also should look at key image parameters such as luminance uniformity, grey levels, white levels, black levels, contrast ratio and brightness. The program should calibrate all criteria to a recommended industry standard such as DICOM or AAPM TG 18, and indicate the responsible party, frequency of calibration, and reporting procedures.

Another option is outsourcing QA. One vendor, Richardson Electronics, recently began offering Teklink QC/QA. The service sends a technician on-site to do a thorough check, calibration, and workstation cleaning that can cover multiple brands of displays. The QC/QA service follows the DICOM Part 14 and AAPM TG 18 guidelines and sends emailed reports that include workstation data, calibration reports, verified visual tests and other calibration parameters.


Study: Most Displays Aren’t Properly Calibrated
A recent study in the British Journal of Radiology (2007; 80, 503-507) that looked at quality assurance of soft-copy display systems found that image quality of most monitors could be improved after calibration.

The study found that about 50 percent of the piloted display systems did not have the maximum luminance (white level) suitably set, and 35 percent lacked the correct minimum luminance (dark level) settings. The results indicate that medical display systems must be carefully selected and strictly monitored, maintained, and calibrated to ensure adequate image quality.