Breast density: Comparison of chest CT with mammography

Purpose: To (a) perform a pilot study comparing radiologists' reading of breast density at computed tomography (CT) of the chest with breast density readings from mammography performed in the same patient and (b) compare a subset of these with computer-derived measurements of breast density at CT. Materials and Methods: The institutional review board waived informed consent for this HIPAA-compliant retrospective review of mammograms and chest CT scans from 206 women obtained within 1 year of each other. Two radiologists with expertise in interpreting mammographic and CT findings independently reviewed the mammograms and CT scans and classified each case into one of the four breast density types defined by the Breast Imaging Reporting and Data System of the American College of Radiology. Interreader agreements for the mammographic density types and CT density grades were determined by using the Cohen weighted k statistic. The intrareader correlation coefficient was determined in a subset of CT images. In another subset of 40 cases, the agreement of the semiautomated computer-derived measurements of breast density with the consensus of the two radiologists was assessed. Results: Interreader agreement was higher for the CT density grades than for the mammographic density types, with 0.79 (95% confidence interval [CI]: 0.73, 0.85) versus 0.62 (95% CI: 0.54, 0.70). The intrareader reliability of breast density grades on CT images was 0.88. The computer- derived breast density measurements agreed with those of the radiologists in 36 (90%) cases. When four cases were manually adjusted for the complex anatomy, there was agreement for all cases. Conclusion: Preliminary results suggest that on further validation, breast density readings at CT may provide important additional risk information on CT of the chest and that computer-derived measurements may be helpful in such assessment.