Influence of Monitor Luminance

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Influence of Monitor Luminance Tone Scale on
Observers Search Dwell Patterns
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Elizabeth Krupinski, PhD Hans
Roehrig, PhDUniversity of ArizonaThis Work
Was Supported in Part byToshiba Medical
Imaging Tokyo, Japan DataRay Corp.
Westminster, CO
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Rationale

• Full-field digital mammography systems will
  soon replace traditional film acquisition
  systems. To maximize the benefits of digital
  mammography (e.g., image processing,
  CAD), we need to understand and
  maximize the properties of CRT
  monitors used to view these
  digital images.

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Purpose

• The goal of this study was to measure the
  influence of display luminance and tone scale
  choice on visual search behaviors. The results of
  this study should be helpful in establishing
  minimally acceptable viewing
  conditions for viewing
  radiographs on CRT monitor
  displays.

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Images

• 50 Pairs Of Mammograms
• - CC MLO views
• - right or left breast
• - 18 mass
• - 18 microcalcification cluster
• - 14 lesion-free
• - All lesions malignant
• - Digitized 80 microns, 12 bits

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Display Monitors
2 DataRay DR110 monitors - Portrait Mode - Size
21 FS - Deflection Angle 90 deg - Active Area
11.5 x 15.5 - Phosphor P-45 - Bulb
Transmission 52 - Panel 92 and 62 -
Resolution 1728 x 2304 - Refresh rate 70 Hz
80 ftL 140 ftL
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Characteristic Curves
Two characteristic curves were selected for the
study. 1) The Barten curve is a perceptually
linearized tone scale. 2) The Default curve is a
non-perceptually linearized tone scale (set using
SMPTE pattern).
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Display Luminance
The two monitors were identical in every
way except for the front panel. 1) Monitor 1 had
a base luminance of 140 ftL. 2) Monitor 2 had a
base luminance of 80 ftL.
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Procedure

• 2 studies
• - changing luminance (140 ftL vs 80 ftL)
• - changing tone scale (Barten vs Default)
• 6 radiologists in each study
• Counterbalanced randomized design
• - Each image seen twice
• - Once in each condition of the study
• - Minimal 2 week separation between sessions
• Unlimited viewing time

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Observers Task

• Determine if a lesion is present or absent
• Indicate if lesion is mass / microcalcification
• Rate confidence in decision on 6-point scale
• 1 no lesion, definite
• 6 lesion present, definite
• Indicate lesion location could indicate more
  than one location
• Detection only, no classification

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Eye-Position Recording

• Eye-position was recorded for each case
• ASL 4000SU Eye-Tracker was used
• Records head movement so observers can
• move while viewing images
  
• Accuracy 1 deg
• Data provides
• - Decision dwell times
• - Number of fixations or clusters
• of fixations landing on image areas
• - Scan patterns

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Typical Search Pattern
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Performance Analyses

• The confidence data were submitted to
  Alternative Free Response Receiver Operating
  Characteristic Analysis (AFROC) and Area Under
  the Curve (A1) values were calculated
• These data were reported in full at the 1998
  SPIE Medical Imaging Conference
  

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Search Analyses

• Eye-position data were analyzed to determine
• - Total viewing times
• - Median decision dwell times
• - Number of fixation clusters
  generated on the mass, microcalcification
  and normal (lesion-free) cases

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Detection Performance

• Barten curve .9720 Default curve .9511
• t 5.423, df 5, p .0029
• 80 ftL monitor .9594 140 ftL monitor
  .9695
• t 1.685, df 5, p .1528
• Average area under the AFROC curve (A1)

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Total View Times - Tone Scale

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Total View Times - Luminance

Lesion-free significantly longer than
mass or microcalcification
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Decision Dwells - Tone Scale
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Decision Dwells - Luminance
C2 4.08 df 1 p 20
Number Of Fixation Clusters Per Case - Tone Scale
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Number Of Fixation Clusters Per Case - Luminance
t 2.83 df 166 p
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Conclusions

• A perceptually linearized display (e.g., using
  the Barten curve) yields significantly better
  detection performance than a non-perceptually
  linearized display
• A 140 ftL display yields marginally better
  detection performance than an 80
  ftL display

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Conclusions

• Visual search is more efficient with the
  perceptually linearized and higher luminance
  displays
• Total view and decision dwells were consistently
  shorter and fewer clusters were generated on all
  types of cases with these displays - especially
  the true-negative decisions and lesion-free images

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Possible Explanation

• Lower luminance and non-linearized displays seem
  to affect most the search and
  evaluation of normal image areas - TN dwell
  times are longer and more clusters are generated
  on lesion-free cases.
• These parameters reflect an increase in
  information processing operations, even though
  the same decisions are reached as with the higher
  luminance and linearized displays.
• Recognizing normal variations in images may be
  more difficult with non-optimal displays, so
  radiologists must alter their search behaviors to
  compensate for display short-comings.

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Conclusions Recommendations

• CRT monitor luminance and tone scale can affect
  diagnostic accuracy and visual search efficiency
  in significant ways.
• For the display of digital mammograms on CRT
  monitors, a relatively high luminance monitor
  should be used and the display should be
  perceptually linearized.