Physical & Psychophysical Evaluation of a Flat-Surface CRT Display

Monitor vs Traditional Curved-Surface Display Monitor for Use in

PACS & TeleradiologyElizabeth Krupinski, PhD1, Hans Roehrig, PhD1

Toshihiko Furukawa, PhD2, Kazuhiro Sato, BEE3

Yoshiaki Iwamo, BEE3

1 University of Arizona

2 DataRay Corporation

3 Totoku-Nagaoka Corporation

Purpose 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.

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 onCRT 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 surfacecurvature 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

Potentialdifficulties when tryingto optimallyevaluate a CRTwith a curvedsurface usinga CCD camera

Monitors EvaluatedTwo 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 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 4 luminance levels (cd/m2)

– 16.5 42.4 81.9* 198.4*

* data collection still in progress

Viewing Conditions Viewing Distance = 50 cm; targets

subtended 2.3 deg visual angle 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/m2

There were 15 observers in each condition

JND Results

0

20

40

60

80

100

120

0 1 2 3 4 5 6 7 8

Gray Level Difference

% C

orre

ct 16.5 F On16.5 F Off16.5 C On16.5 C Off

0

20

40

60

80

100

120

0 1 2 3 4 5 6 7 8

Gray Level Difference

% C

orre

ct 42.4 F On42.4 F Off42.4 C On42.4 C Off

0

20

40

60

80

100

120

0 1 2 3 4 5 6 7 8

Gray Level Difference

% C

orre

ct 81.9 F On81.9 F Off81.9 C On81.9 C Off

JND Results - 50% Correct

Flat Flat Curve Curve

On Off On Off

16.5 1.5 1.3 1.7 1.5

42.4 2.2 1.7 2.5 1.6

81.9 2.4 2.2 3.0 2.4

JND Conclusions 16.5 cd/m2

– Flat surface = no significant difference lights on vs lights off

– Curved surface = lights on significantly worse performance (higher JND) than lights off

42.4 cd/m2

– Both flat & curved surfaces = lights on significantly worse performance than off

– Difference significantly greater for curved

Clinical Images

4 radiologists viewed a series of 10 clinical images side by side on the two monitors

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 displayedphotographed from below (left = flat; right = curved)

SMPTE pattern displayedphotographed straight on(left = flat; right = curved)

Reflections

Lights off monitor onphotographed from below.(left = flat; right = curved)

Lights off monitor onphotographed straight on.(left = flat; right = curved)

Reflections

Lights on monitor offphotographed from below.(left = flat; right = curved)

Lights on monitor offphotographed straight on.(left = flat; right = curved)

Conclusions The major benefit of the flat-surface CRT

appears to be a significant reduction in glare from reflections

It is unlikely that diagnostic performance is affected significantly

Reduced glare/reflections may reduce eye strain & fatigue - this may represent a significant benefit especially for radiologists viewing images for long periods of time