Detectability decreases with off-normal viewing in medical liquid crystal displays.
OBJECTIVE
To quantify the reduction in detection performance of subtle signals at off-normal viewing directions in medical active-matrix liquid crystal displays (AMLCDs).


METHODS
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 0, 30, and 45 degrees from the display normal, along the diagonal axis of a 5 million pixel in-plane switching monochrome AMLCD. The images were generated using white-noise backgrounds. A Gaussian signal was added to the signal-present set with three different signal amplitudes (4, 8, and 12 gray levels in a 10-bit scale).


RESULTS
The average percent correct achieved for a signal of 4 gray levels was 79.6 (95% confidence intervals based on reader and case variability: 71.6-86.9), 63.4 (CI 56.0-71.3), and 55.3 (CI 48.4-62.0), for 0, 30 and 45 degrees from the display normal, respectively. When the signal amplitude was increased by a factor of two, the performance was 76.9 and 57.0 for 30 and 45 degrees, respectively, and 95.3 and 85.3 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.


CONCLUSIONS
Off-normal viewing of diagnostic images in AMLCDs significantly reduces the detection of low-contrast abnormalities. Increased off-normal signal amplitudes were required to regain the detection performance measured for normal viewing. We observed this decrease in detection performance for off-normal viewing even when measured decision times were about twice as long as for normal viewing.
Badano
Aldo
A
NIBIB/CDRH Laboratory for the Assessment of Medical Imaging, Center for Devices and Radiological Health, Food and Drug Administration, Rockville, MD 20857, USA. aldo.badano@fda.hhs.gov
Gallas
Brandon D
BD
D016288:Computer Terminals; D003626:Data Display; D003657:Decision Making; D019544:Equipment Failure Analysis; D006801:Humans; D008027:Light; D050866:Liquid Crystals; D015588:Observer Variation; D010775:Photic Stimulation; D011856:Radiographic Image Enhancement / Q000295:instrumentation; D017603:Signal Detection, Psychological; D012815:Signal Processing, Computer-Assisted; D013647:Task Performance and Analysis; D014584:User-Computer Interface; D014796:Visual Perception