Clinical Feasibility Study of Upright, Low-dose, High-resolution, 3D Breast CT (UBCT).

Inclusion Criteria: For the screening cohort, the inclusion criteria are, women: * (1) who were 40 years of age or older (typical screening age range), and, * (2) who were asymptomatic, and, * (3) who underwent or scheduled to undergo a standard-of-care 2-view bilateral digital breast tomosynthesis screening exam. For the diagnostic cohort, the inclusion criteria are, women: * (1) who were 40 years of age or older, and, * (2) who underwent a standard-of-care 2-view bilateral digital breast tomosynthesis exam, and, * (3) who were assigned BI-RADS category 4 or 5 after diagnostic work-up and are scheduled for biopsy. Exclusion Criteria: * Males * Women less than 40 years old * pregnant or lactating women * women with physical limitations (e.g., kyphosis) that may prohibit UBCT exam * women who have received radiation treatments to the thorax * women who have participated in a prior breast clinical trial that gave additional radiation dose * women who have received large numbers of diagnostic x-ray examinations for monitoring of disease such as tuberculosis, and severe scoliosis.