Rationale and Objectives
Low-dose chest computed tomography (LDCT), increasingly being used for screening of lung cancer, may also be used to measure breast density, which is proven as a risk factor for breast cancer. In this study, we developed a segmentation method to measure quantitative breast density on CT images and correlated with magnetic resonance density.
Materials and Methods
Forty healthy women receiving both LDCT and breast magnetic resonance imaging (MRI) were studied. A semiautomatic method was applied to quantify the breast density on LDCT images. The intra- and interoperator reproducibility was evaluated. The volumetric density on MRI was obtained by using a well-established automatic template-based segmentation method. The breast volume (BV), fibroglandular tissue volume (FV), and percent breast density (PD) measured on LDCT and MRI were compared.
Results
The measurements of BV, FV, and PD on LDCT images yield highly consistent results, with the intraclass correlation coefficient of 0.999 for BV, 0.977 for FV, and 0.966 for PD for intraoperator reproducibility, and intraclass correlation coefficient of 0.953 for BV, 0.974 for FV, and 0.973 for PD for interoperator reproducibility. The BV, FV, and PD measured on LDCT and MRI were well correlated (all r ≥ 0.90). Bland-Altman plots showed that a larger BV and FV were measured on LDCT than on MRI.
Conclusions
The preliminary results showed that quantitative breast density can be measured from LDCT, and that our segmentation method could yield a high reproducibility on the measured volume and PD. The results measured on LDCT and MRI were highly correlated. Our results showed that LDCT may provide valuable information about breast density for evaluating breast cancer risk.
Introduction
Mammographic density has been proven as an independent risk factor for breast cancer . Women with dense breast tissue visible on a mammogram have a cancer risk of 1.8–6.0 times that of women with little density . A great research effort has been devoted to incorporate breast density into risk prediction models to better estimate each individual’s cancer risk. Because the two-dimensional mammography-based measurement is subject to tissue overlapping, thus not able to provide true volumetric information, other emerging technologies based on three-dimensional (3D) imaging for assessing breast density are being developed. Among these new modalities, magnetic resonance imaging (MRI) is most well studied . Although breast MRI is suitable for volumetric analysis and segmentation tools are available, not many women can receive breast MRI because of its high cost. Currently, only high-risk women with lifetime breast cancer risks more than 20% will receive breast MRI for screening .
Low-dose chest computed tomography (LDCT) is increasingly being used for the screening of lung cancer and diagnosis of other pulmonary diseases . According to a report from The National Lung Screening Trial, there was a 20% reduction in deaths from lung cancer among current or former heavy smokers who were screened with LDCT compared to those screened by chest X-ray . The overall average effective dose was approximately 2 mSv for LDCT, which was much lower than an average effective dose of 7 mSv for a typical standard-dose chest CT examination . Despite general radiation concern, LDCT is considered a safe screening tool, and its clinical use is anticipated to increase. Among the examinees, more than 40% are women . As its popularity in clinical practice increases, besides lung cancer screening, LDCT has potential to provide additionalinformation about breast density for personalized management of breast cancer screening.
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Materials and Methods
Subjects
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Imaging Studies
Low-dose Chest Computed Tomography
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Breast MR Imaging
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Breast Segmentation and Quantification of Breast Density
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Breast Density Analyzed From LDCT
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Breast Density Acquired From MRI
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Statistics
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Results
Assessment of Measurement Reproducibility Using LDCT
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Correlation of Breast Density Measured on LDCT and MRI
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Table 1
Breast Density Values Measured From MR and LDCT
Breast Volume (cm 3 ) Fibroglandular Tissue Volume (cm 3 ) Percent Breast Density (%) Maxima Minimum Mean ± SD Maxima Minimum Mean ± SD Maxima Minimum Mean ± SD MR ( N = 40) 1786.7 223.8 616.9 ± 334.8 316.7 9.7 59.7 ± 57.7 34.6 1.6 11.3 ± 9.3 LDCT ( N = 40) 1620.5 296.4 672.8 ± 239.9 394.4 13.0 69.0 ± 62.3 25.2 2.2 10.4 ± 6.1
LDCT, low-dose chest computed tomography; MR, magnetic resonance; SD, standard deviation.
Table 2
Results of Breast Density Measurements in Three Women
BV (Lt/Rt) (cm 3 ) FV (Lt/Rt) (cm 3 ) PD (Lt/Rt) (%) Case 1 ( Fig 5 ) LDCT 646.3/654.5 70.4/76.3 10.9/11.7 MRI 611.4/647.0 61.1/65.9 10.0/10.2 Case 2 ( Fig 6 ) LDCT 479.9/442.9 38.9/38.6 8.1/8.7 MRI 350.7/331.4 30.4/27.9 8.7/8.4 Case 3 ( Fig 7 ) LDCT 517.2/510.5 101.4/97.9 19.6/19.2 MRI 377.3/373.0 88.3/72.6 23.4/19.5
BV, breast volume; FV, fibroglandular tissue volume; LDCT, low-dose chest computed tomography; Lt, left breast; MRI, magnetic resonance imaging; PD, percent breast density; Rt, right breast.
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Discussion
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Acknowledgment
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