Rationale and Objectives
To investigate the impact of breast density on the performance of radiologists when mammograms are digitally acquired and displayed.
Materials and Methods
A total of 150 craniocaudal digital mammograms including 75 cases with cancer were examined by 14 radiologists divided into two groups: those who read more (six) and less (eight) than 2000 mammograms per year. Cases were classified as low or high mammographic density. For both types of cases, detection of cancers within and outside the dense fibroglandular tissue was investigated. The performance of radiologist was measured using jack-knife free-response receiver operating characteristic (JAFROC) figure of merit (FOM).
Results
Radiologists with over 2000 annual reads had significantly higher JAFROC FOM ( P = .03) for high (0.76) mammographic density compared to low (0.70) mammographic density cases. When lesions overlaid the fibroglandular tissue, cases with high mammographic density compared to low mammographic density displayed increased location sensitivity for all radiologists ( P = .03) and for those radiologists reading more than 2000 mammograms annually ( P = .04), whereas JAFROC FOMs increased for all radiologists ( P = .05). No significant changes were observed when the lesion was outside the fibroglandular region.
Conclusions
Increased mammographic density improves the performance of experienced radiologists when using digital mammograms. This finding, which does not align with those previously reported for film screen systems, may be because of windowing/leveling opportunities available with digital images.
Mammography is the leading imaging modality for early detection of breast cancer, and as a screening tool it has significantly decreased breast cancer mortality . Mammographic images depict adipose and fibroglandular tissues, with the latter appearing as visually bright because of its higher attenuation coefficient compared to the more radiolucent adipose tissue . The visual representation of increased amounts of fibroglandular tissue is often referred to as mammographic density .
Previous studies have shown that increased mammographic density is associated with higher risk of missed malignancies and interval cancers , with sensitivity dropping from 80%–98% in fatty breasts to 29%–75% in mammographically dense breasts . In addition, increased numbers of large screen-detected tumors (>15 mm) , higher recall rates , and decreased efficiency of breast screening programs have all been linked to high levels of mammographic density.
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Materials and methods
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Table 1
Demographic Details on Participating Radiologists
Radiologist Grouping Radiologist Number Age Years as a Certified Radiologist Years Reading Mammography Number of Mammograms Read per Year Read over 2000 mammograms/yr 1 43 14 13 20,000 2 61 27 25 5500 3 47 14 13 5000 4 39 12 11 2500 5 56 25 16 2000 6 48 11 5 2000 Mean 49 17.2 13.9 6166.7 Read under 2000 mammograms/yr 7 31 5 2 1000 8 31 3 1 500 9 66 43 20 500 10 42 1.5 1 300 11 36 10 3 100 12 40 12 11 50 13 37 5 1 20 14 ∗ 32 1 1 N/A Mean 39.4 10.1 4.9 352.9
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Selection of Images
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Table 2
Number and Lesion Diameter in High- and Low-Density Cases
Case Type Number of Lesions Median Lesion Diameter (mm) (IQR) Low-density cases 41 12.7 (5.8) High-density cases 37 12 (3.2) Low-density cases with lesion overlaying fibroglandular region 20 11.8 (5.5) Low-density cases with lesion outside fibroglandular region 21 12.8 (6.4) High-density cases with lesion overlaying 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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Table 3
Distribution of Lesion Types Overlaying or Outside the Fibroglandular Dense Tissue
Lesion Type Lesions Overlaying the Fibroglandular Region Lesions outside the Fibroglandular Region Calcification 3 1 Focal asymmetry 8 6 Architectural distortion 10 2 Round ill-defined mass 5 6 Oval ill-defined mass 4 5 Lobular ill-defined mass 4 5 Irregular ill-defined mass 1 2 Round spiculated mass 1 2 Irregular spiculated mass 4 6 Round circumscribed mass 1 2
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Experimental protocol
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Data Analysis
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Results
Impact of Mammographic Density Across all Images
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Table 4
Impact of Mammographic Density Across all Images
Radiologist Grouping Metric Low-Density ∗ Median (IQR) High-Density † Median (IQR)P Value All Location sensitivity 63.8 (23.12) 57.9 (28.94) .12 Specificity 77.0 (25.68) 76.3 (38.16) .41 JAFROC FOM 0.69 (0.09) 0.69 (0.08) .16 Over 2000 mammograms/yr Location sensitivity 67.5 (8.75) 76.3 (22.37) .06 Specificity 71.62 (25.68) 80.27 (35.83) .84 JAFROC FOM 0.70 (0.09) 0.76 (0.12) .03 Under 2000 mammograms/yr Location sensitivity 48.8 (34.38) 54.0 (27.63) .95 Specificity 77.03 (39.19) 76.32 (34.87) .53 JAFROC FOM 0.66 (0.16) 0.67 (0.14) .94
FOM, figure of merit; IQR, interquartile range; JAFROC, jack-knife free-response receiver operating characteristic.
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Impact of Mammographic Density: Lesions Overlaying the Fibroglandular Tissue
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Table 5
Impact of Mammographic Density: Lesion Overlaying the Fibroglandular Tissue
Radiologist Grouping Metric Low-Density ∗ Median (IQR) High-Density † Median (IQR)P Value All Location sensitivity 50.0 (20.84) 59.1 (38.64) .03 Specificity 77.0 (25.68) 76.3 (38.16) .41 JAFROC FOM 0.63 (0.1) 0.68 (0.13) .05 Over 2000 mammograms/yr Location sensitivity 55.6 (12.5) 81.8 (20.64) .04 Specificity 71.62 (25.68) 80.27 (35.83) .84 JAFROC FOM 0.69 (0.08) 0.77 (0.19) .16 Under 2000 mammograms/yr Location sensitivity 41.7 (25.01) 47.7 (27.27) .26 Specificity 77.03 (39.19) 76.32 (34.87) .53 JAFROC FOM 0.61 (0.13) 0.65 (0.14) .21
FOM, figure of merit; IQR, interquartile range; JAFROC, jack-knife free-response receiver operating characteristic.
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Impact of Mammographic Density: Lesion Outside the Fibroglandular Region
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Table 6
Impact of Mammographic Density: Lesion Outside the Fibroglandular Region
Radiologist Grouping Metric Low-Density ∗ Median (IQR) High-Density † Median (IQR)P Value All Location sensitivity 65.8 (35.52) 62.5 (39.06) .22 Specificity 77.0 (25.68) 76.3 (38.16) .41 JAFROC FOM 0.71 (0.14) 0.72 (0.09) .13 Over 2000 mammograms/yr Location sensitivity 73.7 (15.78) 81.3 (35.93) .25 Specificity 71.62 (25.68) 80.27 (35.83) .84 JAFROC FOM 0.71 (0.13) 0.78 (0.15) .14 Under 2000 mammograms/yr Location sensitivity 52.63 (44.74) 56.25 (37.5) .74 Specificity 77.03 (39.19) 76.32 (34.87) .53 JAFROC FOM 0.69 (0.2) 0.70 (0.19) .73
FOM, figure of merit; IQR, interquartile range; JAFROC, jack-knife free-response receiver operating characteristic.
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Discussion
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Conclusions
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Acknowledgments
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