The breast is compressed just as in regular mammography, except the compression paddle has a window. Such a set of images is referred to as a stereo pair. The radiologist selects the center of the lesion, a mass or specific calcifications of a cluster. A computer generates the X, Y and Z coordinates of the targeted lesion. The Z coordinate is the depth of the lesion from the skin.
Some stereotactic units are upright with the patient sitting during the procedure.
Other units include a table where the patient can lie prone with the breast hanging from a hole in the table. The prone table is more comfortable for the patient and decreases the possibility of motion. Once the stereo pair is obtained and the exact location of the lesion is calculated, any of several devices may be employed to obtain tissue sample. The devices differ in the size of the tissue samples obtained the mechanism of obtaining the samples and whether the tissue sampling is noncontiguous, contiguous or possibly complete removal of the lesion. Local anesthesia is used with these devices and a skin incision is made to accommodate the device to be used.