Don't forget color when calibrating imaging displays

2017 02 06 11 12 09 514 Ecr 2017 400

VIENNA - While there still isn't a formal standard for ensuring consistent visualization of the type of color used in many imaging modalities, there are steps that can be taken now to calibrate and perform quality assurance for these displays, according to a presentation at ECR 2017.

For example, a proposed extension to the DICOM Grayscale Standard Display Function (GSDF) will allow for color to be calibrated on these displays, ensuring that subtle differences in color will be easier to perceive and that color images appear similarly on different display systems, according to a team led by Tom Kimpe of display firm Barco.

"And if you [follow the recommendations in the proposed extension,] then you have a display system which not only handles grayscale correctly, but also makes sure your color behavior is correct today and many years in the future if you do calibration regularly," Kimpe said.

The importance of color

Color has become increasingly important in medical imaging and radiology over the past few years, Kimpe said.

"While five years ago most images were still grayscale, today the majority of images include some aspect of color," he said.

Medical imaging modalities such as PET/CT, Doppler ultrasound, and contrast-enhanced MRI rely on "pseudo" color to show, for example, quantitative information on the image, Kimpe said. Fields such as dermatology, however, require accurate representation of absolute color to ensure the correct diagnosis; a small difference in color can lead to a different diagnosis.

"It's clear that color is important in medical imaging," he said. "It's not something fancy; it's something that's really used for the clinical task to be performed."

Failing to provide color calibration can lead to degradation and variability over time for the display of a variety of modalities, he said.


In medical imaging applications that require accurate visualization of absolute color, Kimpe recommends the use of a framework published by the International Color Consortium (ICC) Medical Imaging Working Group.

For imaging applications that rely on pseudocolor, Kimpe suggests a proposed extension to DICOM GSDF called Color Standard Display Function (CSDF). The current DICOM GSDF isn't sufficient to guarantee consistent and qualitative visualization of color; it ensures consistent representation of grayscale, but it doesn't address the color performance of display systems, according to the group.

CSDF, however, employs a color visual difference metric to obtain perceptual linearity of color behavior. The team described CSDF in detail in a paper published online August 4, 2016, in Medical Physics.

The process to get the proposed extension included in a standard is still ongoing, Kimpe said. In addition to the proposed extension to DICOM GSDF, formal standardization of the extension has been initiated as a possible task for the American Association of Physicists in Medicine (AAPM) Task Group 196, which is working on guidelines for proper implementation, utilization, and performance testing of electronic color display monitors intended for medical use.

"If you asked me to guess, it's probably going to take one more year, maybe two years before it becomes an official extension to DICOM, AAPM, or something else," Kimpe said.

In the meantime, Kimpe recommends that "you already do something about the calibration of color, because most radiologists use it daily and it's important," he said.

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