 Clinical evaluation: Four hundred women who will be having breast biopsy as part of their standard care BIRADS 4 and 5 will be recruited to undergo additional imaging prior to biopsy, including research pre-and post-contrast enhanced breast CT imaging of both breasts, as well as standard, FDA approved contrast enhanced breast MRI. The potential of non-contrast enhanced breast CT will be compared using receiver operating characteristic ROC methodology against mammography alone, as well as with mammography tomosynthesis. The breast CT images including both pre-and post-contrast images will be compared using ROC methodology against standard-of-care contrast-enhanced MRI which includes both non-contrast and contrast images. The results of the clinical trials proposed in this investigation should provide strong evidence in regards to the potential of breast CT for breast cancer screening in the normal risk and high risk populations. 