Post on 19-Jan-2018
description
Effects of Grayscale Window/Level on Breast
Lesion DetectabilityJeffrey Johnson, PhD a
John Nafziger, PhD a Elizabeth Krupinski, PhD b
Hans Roehrig, PhD b
baSupported by U. S. Army Medical Research and Materiel Command, grant DAMD-17-01-1-0621
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Rationale
Nearly 50% of breast lesions missed at initial screening are visible retrospectively
Digital mammography could reduce perceptual errors by enhancing lesion conspicuity with image processing
Perceptual models could be useful tools for automating and optimizing techniques for image enhancement
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Overview This study evaluated the use of a visual
discrimination model (VDM) for predicting effects of one type of image enhancement - grayscale window width and level (W/L) - on the detectability of breast lesions
Compared model and observer performance in two experiments:– 2AFC detection thresholds with simulated
mammograms and nonmedical observers– ROC observer performance study with radiologists
and digitized mammograms
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Methods: Simulated Mammograms
Backgrounds– Filtered noise, 1/f3
noise power spectrum– Two groups: Bright and
Dark central regions
Lesion signals– Mass: 2D Gaussian (d=50
arcmin)– Microcalcification cluster:
six blurred disks or “specks” (disk d=8 arcmin, cluster d=40 arcmin)
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Methods: W/L Conditions P-value transformations:
– Fully stretched– Understretched (-25%)– Overstretched (±25%)– Bright shifted (+25%)– Dark shifted (-25%)
Applied to full 512x512 pixel image or 170x170 pixel central region of interest containing lesion
0
256
512
768
1024
0 1024 2048 3072 4096p
p'
Fully stretchedUnderstretched (25%)Overstretched (25%)Bright shifted (25%)Dark shifted (25%)
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Example Test Images
Fullystretched
(FS)
Understretched
(US)
Overstretched
(OS)
GaussianFull W/L
Bright Center
GaussianCentral W/L
Bright Center
SpecksFull W/L
Dark Center
SpecksCentral W/LDark Center
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Example Test Images
Bright shifted(BS)
Dark shifted(DS)
GaussianFull W/L
Bright Center
GaussianCentral W/L
Bright Center
SpecksFull W/L
Dark Center
SpecksCentral W/LDark Center
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2AFC Threshold Detection
Side-by-side presentation of same background with/without signal
Signal amplitude varied in 1-up/3-down staircase procedure; detection threshold at ~80% correct
Five W/L conditions interleaved in same session
Separate sessions for two signal and two background types
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Test Conditions Siemens 5M-pixel CRT monitor (P45) Luminance range = 0.3 to 290 cd/m2
Barco 10-bit display controller DICOM-14 grayscale display function Three nonmedical observers Viewing distance = 52 cm; chin rest Ambient lights off
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Results: Detection Thresholds for Gaussian Signals
0.00
0.03
0.06
0.09
0.12
FullyStretched
UnderStretched
OverStretched
BrightShifted
DarkShifted
W/L Method
Det
ectio
n Th
resh
old
Full W/LCentral W/L
Gaussian on Bright Filtered Noise
0.00
0.03
0.06
0.09
0.12
FullyStretched
UnderStretched
OverStretched
BrightShifted
DarkShifted
W/L Method
Det
ectio
n Th
resh
old
Full W/LCentral W/L
Gaussian on Dark Filtered Noise
Error bars show 95% confidence intervals
Bright Backgrounds Dark Backgrounds
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Results: Detection Thresholds for Speck Clusters
Error bars show 95% confidence intervals
0.00
0.03
0.06
0.09
0.12
0.15
FullyStretched
UnderStretched
OverStretched
BrightShifted
DarkShifted
W/L Method
Det
ectio
n Th
resh
old
Full W/LCentral W/L
Specks on Bright Filtered Noise
0.00
0.03
0.06
0.09
0.12
0.15
FullyStretched
UnderStretched
OverStretched
BrightShifted
DarkShifted
W/L Method
Det
ectio
n Th
resh
old
Full W/LCentral W/L
Specks on Dark Filtered Noise
Bright Backgrounds Dark Backgrounds
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Experimental Detection Thresholds
Significant variations across W/L conditions Generally lower for central vs. full W/L
– due to local contrast enhancement- fully stretched not always optimal
Full W/L: Lowest thresholds for …– fully stretched, understretched (specks only)– dark shifted on bright, bright shifted on dark
Central W/L: Lowest thresholds for …– overstretched for Gaussians and specks on dark– dark shifted on bright, bright shifted on dark
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Visual Discrimination Modeling
Simulates physiological response of human visual system to visual stimuli: luminance patterns from images & video
Output is a deterministic prediction of feature or image discriminability as function of spatial location, spatial frequency, and time
Discriminability measured in units of Just Noticeable Differences (JND)
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VDM Architecture
…
JND scalar
Spatial frequencybands
Spatial orientation responses
Display& Ocular
Processing
Optics
Crossband Masking
JND map
JND Distance
Combin. Rule
Display luminance
Pair of input images
Probability
Contrast Pyramid (visual cortex)
Within-band Masking
Contrast Pyramid
…
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VDM vs. Experimental Thresholds for Gaussians on Bright
Backgrounds
0.00
0.03
0.06
0.09
0.12
FullyStretched
UnderStretched
OverStretched
BrightShifted
DarkShifted
W/L Condition
Con
tras
t Thr
esho
ld
ExperimentalModel
Gaussian on BrightFiltered Noise: Full W/L
Error bars show 95% confidence intervals
0.00
0.03
0.06
0.09
0.12
FullyStretched
UnderStretched
OverStretched
BrightShifted
DarkShifted
W/L Condition
Con
tras
t Thr
esho
ld
ExperimentalModel
Gaussian on BrightFiltered Noise: Central W/L
Full W/L Central W/L
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VDM vs. Experimental Thresholds for Gaussians on Dark Backgrounds
Error bars show 95% confidence intervals
0.00
0.03
0.06
0.09
0.12
FullyStretched
UnderStretched
OverStretched
BrightShifted
DarkShifted
W/L Condition
Con
tras
t Thr
esho
ld
ExperimentalModel
Gaussian on DarkFiltered Noise: Full W/L
0.00
0.03
0.06
0.09
0.12
FullyStretched
UnderStretched
OverStretched
BrightShifted
DarkShifted
W/L Condition
Con
tras
t Thr
esho
ld
ExperimentalModel
Gaussian on DarkFiltered Noise: Central W/L
Full W/L Central W/L
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VDM vs. Experimental Thresholds for Specks on Bright Backgrounds
Error bars show 95% confidence intervals
0.00
0.04
0.08
0.12
0.16
FullyStretched
UnderStretched
OverStretched
BrightShifted
DarkShifted
W/L Condition
Con
tras
t Thr
esho
ld
ExperimentalModel
Specks on BrightFiltered Noise: Full W/L
0.00
0.04
0.08
0.12
0.16
FullyStretched
UnderStretched
OverStretched
BrightShifted
DarkShifted
W/L Condition
Con
tras
t Thr
esho
ld
ExperimentalModel
Specks on BrightFiltered Noise: Central W/L
Full W/L Central W/L
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VDM vs. Experimental Thresholds for Specks on Dark Backgrounds
Error bars show 95% confidence intervals
0.00
0.04
0.08
0.12
0.16
FullyStretched
UnderStretched
OverStretched
BrightShifted
DarkShifted
W/L Condition
Con
tras
t Thr
esho
ld
ExperimentalModel
Specks on DarkFiltered Noise:
Full W/L
0.00
0.04
0.08
0.12
0.16
FullyStretched
UnderStretched
OverStretched
BrightShifted
DarkShifted
W/L Condition
Con
tras
t Thr
esho
ld
ExperimentalModel
Specks on DarkFiltered Noise: Central W/L
Central W/LFull W/L
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VDM vs. Experimental Thresholds: Simulated Lesions & Backgrounds
Generally good agreement between model and experimental detection thresholds and variations across W/L conditions
Consistently reduced thresholds with central (local ROI) vs. full-image W/L
Largest modeling discrepancies for specks, especially on dark backgrounds
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ROC Observer Study
Determine effects of W/L functions and size on detection of microcalcification clusters by mammographers
Evaluate utility of localized ROI contrast enhancement (central vs. full W/L)
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ROC Observer Study: Image Preparation
Digitized mammograms (n=15) from Digital Database for Screening Mammography
Extracted 512x512-pixel sections with single, centered microcalcification cluster
Removed calcifications by median filtering Generated five lesion-contrast levels: 0, 25, 50, 75,
and 100% Applied three W/L functions: Fully stretched, under
and over stretched by 15% Full and Central W/L sizes
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ROC Observer Study: Test Conditions
6 radiologists at Univ. of Arizona 225 images/session 2 reading sessions ~2 weeks apart Decision confidence on 6-point scale No image processing, no time limits,
ambient lights off; viewed at ~25 cm Siemens 5M-pixel CRT monitor (P45) Luminance = 0.8 to 500 cd/m2
DICOM-14 grayscale display function
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Examples of Test ImagesUnderstretched
(US, 15%) Overstretched
(OS, 15%) Fully stretched(FS, 0-4095)
FullW/L
CentralW/L
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ROC Observer Study: Results Compared central vs. full W/L across all W/L functions, all lesion
contrasts Observer performance statistically better (p<0.05) for FULL W/L size
Az Values
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ROC Observer Study: Results No statistically significant variations:
– between central and full W/L sizes for a single W/L function (all lesion contrasts)– between central and full W/L sizes for a single combination of W/L function and lesion contrast (except FS,
50%)– across W/L functions in central and full W/L sizes considered separately (all lesion contrasts)
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ROC Observer Study: Analysis Central W/L enhanced lesion contrast but changed appearance of parenchymal tissue relative to surrounding
areas Decision confidence lowered by nonuniform appearance of background tissue characteristics Conclusion: Calcifications may be easier to perceive (due to higher contrast) but more difficult to interpret (due
to cognitive factors, past experience)
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Conclusions For simulated lesions and backgrounds, VDM was generally a reliable predictor of W/L conditions for optimal detectability
Results with simulated images suggested benefits of localized contrast enhancement
Decision confidence and performance of mammographers actually lower with localized W/L, probably due to nonuniform tissue appearance
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Future Directions Allow toggling between full and local W/L modes (combine uniform contextual data with local contrast enhancement) Evaluate effects of W/L on detection of very subtle lesions (low contrast, near threshold) Model refinements:
– improved crossband masking for higher frequency signals: specks/calcifications– include effects of background noise via statistical observer model