Influence of Monitor Luminance & Tone Scale on Observers’ Search & Dwell Patterns

1. Influence of Monitor Luminance & Tone Scale on Observers’ Search & Dwell Patterns

2. Elizabeth Krupinski, PhD & Hans Roehrig, PhDUniversity of ArizonaThis Work Was Supported in Part by:Toshiba Medical Imaging Tokyo, Japan DataRay Corp. Westminster, CO

3. 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.

4. 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.

5. 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

6. 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

7. Monitor 1 (140 ftL) Default - - - Barten ------ 120.00 ) Monitor 2 (80 ftL) L - t f ( - - - Default e 80.00 c n ------ Barten a n i m u L 40.00 0.00 0.00 100.00 200.00 300.00 Command Level (ADU) Characteristic Curves Two characteristic curves were selected for the study. 1) The Bartencurve is a perceptually linearized tone scale. 2) The Default curve is a non-perceptually linearized tone scale (set using SMPTE pattern).

8. Output Luminance versus Beam Current for 160.00 Data Ray Monitor DR 110 with P45 Phosphor and 92 % Panel (Monitor 1) and 62 % Panel (Monitor 2) 120.00 Monitor 1 (140 ftL) ] L - t f [ e c n a n i 80.00 m u L t u p t Monitor 2 (80 ftL) u O 40.00 0.00 100.00 200.00 300.00 400.00 Beam Current [micro-A] 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.

9. 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

10. 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

11. 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

12. Typical Search Pattern

13. 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

14. 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

15. 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)

16. Total View Times - Tone Scale

17. Total View Times - Luminance * Lesion-free significantly longer than mass or microcalcification

18. Decision Dwells - Tone Scale

19. Decision Dwells - Luminance * C2 = 4.08 df = 1 p < 0.05

20. Number Of Fixation Clusters Per Case - Tone Scale

21. Number Of Fixation Clusters Per Case - Luminance * t = 2.83 df = 166 p < 0.01 *

22. 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

23. 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

24. 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.

25. 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.