Interest in nuclear breast imaging is increasing because of technical improvements in dedicated devices that allow the use of relatively low doses of radiotracers with high sensitivity for even small breast cancers. For women with newly diagnosed cancer, primary chemotherapy is often recommended, and improved methods of assessing treatment response are of interest. With widespread breast density notification, functional rather than anatomic methods of screening are of increasing interest as well. For a cancer imaging technology to be adopted, several criteria must be met that will be discussed: evidence of clinical benefit with minimal harm, standardized interpretive criteria, direct biopsy guidance, and acceptable cost-effectiveness. Twor adiotracers have been used widely to depict breast cancer: the g-emitting 99m Tc-sestamibi ( 99m Tc-methoxyisobutylisonitrile), 140 keV, half-life of 6 h, originally developed as a myocardial perfusion agent; and the positron-emitting glucose analog 18 F-FDG, 511 keV, half-life of 2 h. Standard lead shielding as is used in a mammography suite is sufficient when using 99m Tc-sestamibi. Using 18 F-FDG requires much more extensive shielding and may not be feasible because of workspaces above or below the planned unit. State licensing requirements for nuclear medicine must be considered; typically, a hot lab with oversight by a trained nuclear medicine technologist and a physicist is required (1).Both 99m Tc-sestamibi and 18 F-FDG were initially studied for breast cancer using whole-body scanners. Low sensitivity to invasive cancers smaller than 1 cm was observed with whole-body g-camera imaging in a prospective multicenter series at 48.2%, compared with 74.2% for larger tumors (2); detection of small cancers, particularly small invasive cancers, is a major goal of breast imaging. Similar results were observed with whole-body PET, with sensitivity to invasive tumors 2 cm or smaller of only 30 of 44 (68%) compared with 57 of 62 (92%) for larger cancers (3).Dedicated breast g-camera imaging can be performed with singledetector scintillating-crystal systems such as breast-specific g-imaging (BSGI) (Dilon Technologies) with a 20 · 15 cm field of view, 3.3-mm pixel size; or using dual-head cadmium-zinc-telluride detector systems, often referred to as molecular breast imaging (MBI) (GE Healthcare, with a 24 · 16 cm field of view and 2.5-mm pixel size; or Gamma Medica, Inc., with a 20 · 16 cm field of view and 1.6 mm pixel size). Both approaches use positioning similar to that of mammography, with the breast gently stabilized between a compression paddle and the detector (BSGI) or between 2 detectors (MBI). It is important to include mammographic technologists in the positioning of the patients, at least for a minimum number of cases (e.g., 25), to ensure full inclusion of posterior tissues for both a craniocaudal and a mediolateral oblique (MLO) acquisition. Particularly with the dualhead systems, it can be difficult to prevent skin folds or to ensure that the nipple is in profile becau...