Rationale and Objectives
To determine the impact of mammographic breast density on the visual search process of radiologists when reading digital mammograms.
Materials and Methods
Institutional review board approval was obtained. A set of 149 craniocaudal digital mammograms were read by seven radiologists, and observer search patterns were recorded. Total time examining each case, time to first hit the lesion, dwell time, and number of hits per area were calculated. The nonparametric Mann–Whitney U test was used for statistical evaluation.
Results
In both low- and high-mammographic density cases, significant increases were observed in the time to first hit lesions when they were located outside, compared to overlying fibroglandular dense tissue ( P = .001). Significantly longer dwell time ( P = .003) and greater number of fixations ( P = .0003) were observed when the lesions were situated within—rather than outside—the dense fibroglandular tissue.
Conclusions
Increased mammographic breast density changes radiologists’ visual search patterns. Dense areas of the parenchyma attracted greater visual attention in both high- and low-mammographic density cases, resulting in faster detection of lesions overlying the fibroglandular dense tissue, along with longer dwell times and greater number of fixations, as compared to lesions located outside the dense fibroglandular regions.
Mammography is the only proven screening tool for early detection of breast cancer, and it has been shown to significantly decrease breast cancer mortality . Mammograms display the main components of the breast, namely adipose and fibroglandular connective tissues, with the latter appearing whiter than the former because of increased attenuation properties . Mammographic density refers to the proportion of fibroglandular tissue that is displayed relative to the remaining parts of the breast.
It is well reported that, with film technology, high mammographic density reduces the radiologists’ ability to detect cancer, as sensitivity decreased from 80%–98% in fatty breasts to 29.2%–75% in dense breasts . This led to greater numbers of missed cancers , interval cancers , recall rates , and screen-detected tumors of >15 mm in size . Moreover, mammographic specificity was lower in dense breasts , decreasing from 96.9% in women with almost entirely fatty breasts to 89.1% in extremely dense breasts .
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Materials and methods
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Table 1
Demographic Details on Participating Radiologists
Radiologist Number Age Years Reading Mammograms Average Mammograms Read Per Year 1 43 13 20,000 2 61 25 5500 3 47 13 5000 4 48 5 2000 5 31 2 1000 6 31 1 500 7 40 11 500 Mean 43.0 10 4928.6
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Cases
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Table 2
Median Lesion Diameter in Low- and High-Mammographic Density Cases When the Lesions Outside—and When They Overlie—the Dense Fibroglandular Tissue
Case Type Number of Cases Median Lesion Diameter, mm (IQR) Low-density cases 37 12.8 (6.3) High-density cases 37 12 (4.1) Low-density cases with lesion overlying fibroglandular region 18 11.7 (5.7) Low-density cases with lesion outside fibroglandular region 19 12.8 (6.6) High-density cases with lesion overlying fibroglandular region 21 12.0 (5.2) High-density cases with lesion outside fibroglandular region 16 11.6 (2.3)
IQR, interquartile range.
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Experimental Protocol
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Data Analysis
Normalized Breast Size
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Lesion Type and Diameter
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Eye Position Analysis
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Results
Normalized Breast Size
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Lesion Type and Diameter
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Eye Position Analysis
Lesion Detectability
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Effect of Mammographic Density on the Radiologists’ Visual Search in Malignancy-Containing Mammograms
Effect of lesion location
In low-density cases
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Table 3
Lesion Location: Effect in Low-Density Mammograms
Category Lesion Overlying Fibroglandular Tissue ( n = 18) Lesion Outside Fibroglandular Tissue ( n = 19)z__P Total time examining a case 7.81 (9.61) 7.17 (8.66) −0.97 .33 Time to first hit the lesion 2.28 (12.01) 8.44 (27.71) −3.43 .001 Dwell time Background 4.91 (5.77) 4.38 (5.16) −0.64 .52 Dense 0.72 (1.60) 0.97 (1.70) −2.67 .01 Lesion 1.76 (4.01) 1.13 (2.26) −2.98 .003 Number of hits per area Background 18 (14.0) 18 (17.25) −0.01 .10 Dense 3 (7.0) 5 (8.25) −3.39 .001 Lesion 7 (8.0) 4 (6.0) −3.58 .0003
IQR, interquartile range.
Median values (IQR) are shown. Times are shown in seconds.
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In high-density cases
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Table 4
Lesion Location: Effect in High-Density Mammograms
Category Lesion Overlying Fibroglandular Tissue ( n = 21) Lesion Outside Fibroglandular Tissue ( n = 16)z__P Total time examining a case 8.45 (10.75) 7.60 (8.96) −1.37 .17 Time to first hit the lesion 7.96 (16.64) 12.63 (14.25) −3.48 .001 Dwell time Background 5.17 (6.05) 4.64 (4.63) −1.19 .24 Dense 1.26 (2.50) 1.65 (2.77) −1.04 .30 Lesion 1.67 (2.97) 1.04 (1.38) −3.56 .0004 Number of hits per area Background 20 (17.0) 17 (15.0) −0.85 .39 Dense 6 (9.75) 7 (12.50) −1.18 .24 Lesion 6 (8.0) 4 (5.0) −4.10 <.0001
IQR, interquartile range.
Median values (IQR) are shown. Times are shown in seconds.
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Effect of case density
Lesions overlying the fibroglandular dense tissue
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Lesions outside the fibroglandular dense tissue
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Effect of Mammographic Density in Malignancy-Free Mammograms
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Table 5
Malignancy-Free Cases: Effect of Mammographic Density on Radiologists’ Visual Search
Category Low Density ( n = 37) High Density ( n = 38)z__P Total time examining a case 6.48 (7.32) 9.85 (8.99) −1.42 .17 Dwell time Background 4.08 (4.46) 5.61 (5.0) −0.91 .38 Dense 2.21 (2.94) 4.14 (4.11) −2.28 .02 Number of hits per area Background 17 (14.75) 21 (17.0) −1.60 .13 Dense 9 (9.0) 17 (14.0) −2.63 .01
IQR, interquartile range.
Median values (IQR) are shown. Times are shown in seconds.
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Discussion
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Acknowledgments
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