Cite this article as: Bansal GJ, Kotugodella S. How does semi-automated computer-derived CT measure of breast density compare with subjective assessments to assess mean glandular breast density, in patients with breast cancer? Br J Radiol 2014;87:20140530. FULL PAPER How does semi-automated computer-derived CT measure of breast density compare with subjective assessments to assess mean glandular breast density, in patients with breast cancer? Methods: A retrospective review of mammograms and CT scans in 77 patients with breast cancer obtained within 1 year of each other was performed. Two radiologists independently reviewed both CT and mammograms and classified each case into four categories as defined by the breast imaging-reporting and data system of the American College of Radiology. Inter-reader agreements were obtained for both mammographic and CT density subjective evaluations by using the Cohen-weighted kappa statistic and Spearman correlation. The semi-automated computer-derived measurement of breast density was correlated with visual measurements.Results: Inter-reader agreements were lower for subjective CT density grades than those for mammographic readings 0.428 [confidence interval (CI), 0.24-0.89] vs 0.571 (CI, 0.35-0.76). There was moderately good correlation between subjective CT density grades and the mammographic density grades for both readers (0.760 for Reader 1 and 0.913 for Reader 2). The semi-automated CT density measurement correlated well with the subjective assessments, with complete agreement of the density grades in 84.9% of patients and only one level difference in the rest. Conclusions: Semi-automated CT density measurements in the evaluation of breast density correlated well with subjective mammographic density measurement. Advances in knowledge: There is good correlation between CT and mammographic density, but further studies are needed on how to incorporate semi-automated CT breast density measurement in the risk stratification of patients.High glandular density on mammograms has been identified as a risk factor for development of breast cancer. [1][2][3] Moreover, mammograms of breasts with high glandular density have low sensitivity for diagnosing breast cancer. There has been an impetus to use methods other than traditional mammograms to evaluate breasts with high density such as ultrasound and MRI. 4,5 On the other hand, CT scans are increasingly performed in a variety of age groups for reasons other than breast symptoms. Following recent recommendations of low-dose chest CT screening for lung cancer in high-risk patients, 6 many females have had CT of the chest performed but not mammograms. We believe that CT provides a valuable resource to get reliable information with respect to breast density. If breast density can be determined accurately and is deemed to be high on CT scan, there is a case to suggest supplemental screening with other modalities in addition to mammography.The aim of this study is to evaluate (1) if semi-automated CT measurement of density is a reliabl...