Physical & Psychophysical Evaluation of a Flat-Surface CRT Display Monitor vs Traditional Curved- Surface Display Monitor for Use in PACS & Teleradiology Elizabeth Krupinski, PhD 1, Hans Roehrig, PhD 1 Toshihiko Furukawa, PhD 2, Kazuhiro Sato, BEE 3 Yoshiaki Iwamo, BEE 3 1 University of Arizona 2 DataRay Corporation 3 Totoku-Nagaoka Corporation

Purpose n Radiographs based on the familiar projection imaging are planar & are placed on a flat surface light box for viewing. Presenting digital radiographs on a CRT with a curved surface may cause distortions & increase reflections from ambient light. n To demonstrate that CRT displays with a flat surface are superior to CRT displays with a curved surface.

Why is the Display Important?

Distortions occurring when planar radiographs are presented on a display (CRT) with a curved surface Planar radiograph Radiograph presented on CRT with curved surface

Curved CRT A straight-edge (black strip) was placed against the monitor surface. The SMPTE pattern was displayed. Note the effect of monitor surface curvature on the straight line of the SMPTE pattern to the right of the straight-edge. The line looks “bowed”. This could affect the accuracy of a radiologist measuring the length of, for example, a bone.

Flat CRT A straight-edge (black strip) was placed against the monitor surface. The SMPTE pattern was displayed. Note that there is no “bowing” of the line of the SMPTE pattern. The radiologist is more likely to obtain an accurate measure with the flat-surface CRT.

Measurement of CRT performance parameters with a CCD camera

Potential difficulties when trying to optimally evaluate a CRT with a curved surface using a CCD camera

Monitors Evaluated Two DataRay DR96 monochrome (1600 x 1200) portrait CRT monitors – One had the traditional curved- surface (C) glass faceplate – One had a new flat-surface (F) glass faceplate – Both calibrated to the DICOM 14 standard

Measurement of Veiling Glare (Image of a Circle)

Veiling Glare

Display Functions

Uniformity Uniformity of Curved CRT

Psychophysical Evaluation n Stimuli = grating (bar) patterns – 7 pixels on & 7 pixels off (2 cm x 2 cm) – 11 bars total – 10 horizontal & 10 vertical renditions of each of 9 gray levels 63 blank (no bars) controls n 4 luminance levels (cd/m 2 ) – * 198.4* * data collection still in progress

Viewing Conditions n Viewing Distance = 50 cm; targets subtended 2.3 deg visual angle n All series of images were viewed twice –Once with all ambient room lights off –Once with all ambient room lights on –The difference was ~ 10 cd/m 2 n There were 15 observers in each condition

JND Results

JND Results - 50% Correct Flat Flat Curve Curve On Off On Off

JND Conclusions n 16.5 cd/m 2 –Flat surface = no significant difference lights on vs lights off –Curved surface = lights on significantly worse performance (higher JND) than lights off n 42.4 cd/m 2 –Both flat & curved surfaces = lights on significantly worse performance than off –Difference significantly greater for curved

Clinical Images n 4 radiologists viewed a series of 10 clinical images side by side on the two monitors n All reported that they preferred the flat surface monitor because of lower reflections, but could not see any differences in terms of available diagnostic information

Reflection of room lights & other light emitting structures off CRTs with flat & curved surfaces

Reflections SMPTE pattern displayed photographed from below (left = flat; right = curved) SMPTE pattern displayed photographed straight on (left = flat; right = curved)

Reflections Lights off monitor on photographed from below. (left = flat; right = curved) Lights off monitor on photographed straight on. (left = flat; right = curved)

Reflections Lights on monitor off photographed from below. (left = flat; right = curved) Lights on monitor off photographed straight on. (left = flat; right = curved)

Conclusions n The major benefit of the flat-surface CRT appears to be a significant reduction in glare from reflections n It is unlikely that diagnostic performance is affected significantly n Reduced glare/reflections may reduce eye strain & fatigue - this may represent a significant benefit especially for radiologists viewing images for long periods of time