The tools for mammography and its interpretation have undergone a Renaissance over the past couple decades. Film-screen mammography and the classic light-box alternator diagnostic paradigm are rapidly giving way to full-field digital mammography (FFDM) acquisition with DR and CR technology and soft-copy interpretation, either on cathode ray tube or flat-panel liquid crystal displays (LCDs).
The introduction of LCD panel displays in the commercial off-the-shelf computer space has thoroughly supplanted CRT-based monitors for the consumer market. The filmless reading room in radiology also has seen a surge in deployment, in part due to the reduced footprint, easier quality assurance, and longer lifetime of LCD monitor technology.
Flat-panel displays have made great strides in the medical marketplace since their introduction. A combination of liquid-crystal processes tuned for medical applications, greater noise reduction as well as more uniform, stable and powerful backlit illumination have eliminated many of the previous drawbacks of LCDs.
In 2005, Elizabeth Krupinski, PhD, from University Medical Center in Tucson, Ariz., noted that care should be taken when viewing radiographic images off axis on LCD displays.
“Residents and other clinicians who tend to find themselves seated next to or looking over the shoulder of the radiologist seated in front of the display need to be aware of the fact that the LCD display distorts luminance, gray levels and contrast and that these distortions can lead to degradations in performance especially for low-contrast lesions,” she wrote in the Proceedings of SPIE (Vol. 5749).
In the intervening years, LCD panel manufacturers have addressed this issue through the utilization of in-plane switching, which maintains high contrast over a much larger viewing angle—of particular importance in dual- and quad-monitor configurations commonly deployed for radiological reading environments.
The physical characteristics and quality of display are of great import for any diagnostic imaging interpretation, and particularly so in digital mammography. Luminance, contrast, resolution, sharpness, and uniformity across the display are critical for diagnostic-quality digital mammography display. High spatial requirements necessary to display subtle gradations in shading, and the very small details within that shading, have made this sub-specialty among the last to migrate from CRT to LCD monitors.
However, a cornucopia of 5 megapixel (MP) and higher offerings from display developers that meet the specific needs of the sub-specialty, and approved by the FDA for primary interpretation of digital mammograms, is rapidly elbowing out conventional CRT monitors in many mammography reading rooms. In addition, multi-site, scientific studies have confirmed the efficacy of LCD technology for digital mammography interpretation.
Research published in the American Journal of Roentgenology (Dec. 2006) found that 5MP flat-panel monitors are at least equivalent to, and in some aspects superior to, 5MP CRTs in the display of FFDM images.
“As we move out of the research arena with digital mammography and into the high-volume use of this technology, it is imperative that we work to make this technique fit into our preexisting PACS systems,” the authors note. “In doing so, we will help control the overall costs of the systems both in dollars spent and in interpretation time. Because LCD monitors are now widely used for the primary interpretation of other techniques, it seemed logical to evaluate their use for mammography.”
The study determined that the LCDs were rated better for the sharpness of mass margins and mass conspicuity. For calcium features, the LCDs were rated better than the CRTs for lesion conspicuity and number of calcifications
For architectural distortions, there was no statistically significant difference between the monitors in any of the features evaluated. For display characteristics, the LCDs were better for luminance, while the CRTs were significantly better for image noise. In the overall ratings, there was no statistically significant difference between the two displays.
Optimizing flat-panel deployment
When it comes to soft-copy interpretation of digital mammography images in the reading room trenches, LCD monitors trump CRTs for a host of