LCD technology counteracts spatial noise at pixel level

August 29, 2005

Spatial noise has plagued users of LCD monitors since these displays entered radiological use several years ago. The noise appears as stationary differences in the behavior of individual pixels. It can shroud critical details, leading in extreme cases to missed pathologies, particularly in the most demanding radiological tasks such as reading digital mammograms. Now Barco, an early proponent of LCDs in medical imaging, claims to have a solution.

Spatial noise has plagued users of LCD monitors since these displays entered radiological use several years ago. The noise appears as stationary differences in the behavior of individual pixels. It can shroud critical details, leading in extreme cases to missed pathologies, particularly in the most demanding radiological tasks such as reading digital mammograms. Now Barco, an early proponent of LCDs in medical imaging, claims to have a solution.

The Belgian developer of display hardware and image processing software has come up with a way to correct spatial noise in real-time on images sent to high-resolution medical LCD monitors. The Barco technology employs a technology called per pixel uniformity (PPU) that maps the noise behavior of each of the millions of individual pixels in LCDs, then "precompensates" for aberrant behavior in the images as they are sent for display.

"This system removes all display noise transparently to the user," said Tom Kimpe, president of Barco Imaging. "If one knows exactly the noise pattern that will be superimposed on the medical image, then it becomes possible to change, or precompensate, the image so that the noise pattern is canceled."

The presence of spatial noise, which is inherent in liquid crystal technology, has raised questions regarding the usefulness of LCDs when performing subtle clinical diagnoses, such as those in mammography. PPU solves the problem by ensuring the correct presentation of pixels, a noteworthy accomplishment considering the magnitude of the problem.

Each of the millions of individual pixels is a separate element with its own characteristics, which depend on factors such as local thickness of the glass and the tolerance of the transistor driving that specific pixel. As a result, each pixel present in an active matrix medical LCD behaves differently, Kimpe said.

"Even if all pixels were driven with exactly the same pixel data, there would still be a measurable difference in luminance between individual pixels," he said.

PPU increases uniformity and decreases spatial noise to a level superior to noncompensated LCDs and even better than CRT devices built for mammography, according to Kimpe. Without individual compensation, most pixels would be outside the tolerance recommended by the American Association of Physicists in Medicine and the European Reference Organization for Quality Assured Breast Screening and Diagnostic Services.

"Especially for subtle mammography diagnosis, PPU could be an important step forward. Noise compensation almost completely removes all systematic static noise patterns from the display, thereby reducing the risk of false positives and increasing the probability of detection of true structures in the image," Kimpe said.