A system and method for breast imaging using x-ray computed tomography (CT) are provided. One system includes a rotating gantry, an x-ray source coupled to the gantry for generating an x-ray beam and an x-ray detector coupled to the gantry for detecting x-rays of the x-ray beam. The system further includes an adjustable collimator coupled to the x-ray source and configured to adjust a focus of the x-ray beam generated by the x-ray source. The x system also includes a controller configured to control the collimator to adjust the focus on a region of interest (ROI) and to control a beam intensity for the x-ray beam generated by the x-ray source during a scan.