Aldo Badano PhD, Presenter: Nothing to Disclose

Brandon D. Gallas, Abstract Co-Author: Nothing to Disclose

To quantify the decrease in detection performance of subtle signals at off-normal viewing directions in medical active-matrix liquid crystal monitors (AMLCDs).

Fifty synthetic image pairs per viewing condition (a total of 350) were used in a two-alternative forced choice experiment in which 11 trained observers viewed images at zero, thirty, and forty-five degrees from the display normal, along the diagonal axis of a five-million-pixel in-plane-switching monochrome AMLCD. The images were generated using independently realized white noise backgrounds with a variance of 20. In the signal-present images, a Gaussian signal was added with three different signal amplitudes (4, 8, and 12 gray levels in a 10-bit scale). The time required by each observer to record a decision was measured.

The average percent correct achieved by 11 observers for a signal amplitude of 4 gray levels was 0.796 (95% confidence intervals based on reader and case variability: 0.716/0.869), 0.634 (0.560/0.713), and 0.553 (0.484/0.620), for normal viewing, 30 and 45° from the display normal respectively. When the signal amplitude was increased by a factor of two, the performance was 0.769 (0.682/0.847) and 0.570 (0.480/0.665) for 30 and 45° respectively. The performance was elevated to 0.953 (0.874/0.996) and 0.853 (0.713/0.960) for 30 and 45° respectively, when the amplitude was increased by a factor of three. The observers took on average about twice as long and as much as seven times as long to reach decisions in off-normal viewing.

Off-normal viewing of diagnostic images in non-Lambertian displays (such as current AMLCDs) significantly reduces the detection of low-contrast abnormalities. An increase in signal amplitude of a factor of about two in the images viewed at 30° was required to regain the detection performance measured for the normal viewing condition. Signals with three times the amplitude were needed to obtain similar detection performance between 45° and normal viewing. We observed this decrease in detection performance for off-normal viewing even when the measured decision times were about twice as long as for normal viewing.

A.B.,B.D.G.: Equipment loans provided by BARCO, FIMI/PHILIPS, National Display Systems, and PLANAR

Badano, A, Gallas, B, Detectability Decreases with Off-normal Viewing in Medical Liquid Crystal Displays.  Radiological Society of North America 2005 Scientific Assembly and Annual Meeting, November 27 - December 2, 2005 ,Chicago IL. http://archive.rsna.org/2005/4408625.html