Full-field breast tomosynthesis.

Breast tomosynthesis is a 3-dimensional (3-D) imaging technology that involves acquiring images of a stationary compressed breast at multiple angles during a short scan. The individual images are then reconstructed into a series of thin high-resolution slices that displayed individually or in a dynamic ciné mode. Tomosynthesis can reduce or eliminate the tissue overlap effect. While holding the breast stationary, images are acquired at a nsumber of different x-ray source angles. Objects at different heights in the breast project differently for each angle. The final step in the tomosynthesis procedure is reconstructing the data to generate images that enhance objects from a given height by appropriate shifting of the projections relative to one another. There are 3 specific areas in tomosynthesis system requirements that warrant a closer review: detector efficiency and dose, field of view, and equipment geometry. The breast is compressed in a standard way. While holding the breast stationary, the x-ray tube is rotated over a limited angular range. A series of low dose exposures are made every few degrees, creating a series of digital images. Typically, the tuben is rotated about +/-15 degrees, and 11 exposures are made every 3 degrees during a total scan of a few seconds. The individual images are projections through the breast at different angles and these arewhat are reconstructed into slices. There are 2 basic tomosynthesis system designs that diiffer in the motion of the detector during acquisition. One method moves the detector in concert with the x-ray tube so as to maintain the shadow of the breast on the detector. An altemate method is to keep the detector stationary relative to the breast platform. The tomosynthesis reconstruction process consists of computing high-resolution images whose planes are parallel to the breast support plates. Typically, these images are reconstructed with slice separation of 1 mm; thus, a 5 cm compressed breast tomosynthesis study will have 50 reconstructed slices. The reconstructed tomosynthesis slices can be displayed similarly to computed tomography (CT) reconstructed slices. Tomosynthesis could resolve many of the tissue overlap reading problems that are a major source of the need for recalls and additional imaging in 2-D mammography exams.