Review of the raw projection data from routine MPI may reveal incidental breast pathology (Table 6.1) (Gedik et al. 2007; Raza et al. 2005a, b). The left and most of the right breast are included in the field-of-view during routine SPECT MPI. A variety of benign conditions tend to show a diffuse and symmetric pattern (Fig. 6.1) (Chamarthy and Travin 2010). Lactating breasts (Fig. 6.2) will show varying degrees of bilaterally symmetric increased uptake depending on the postpartum state and breastfeeding status (Ramakrishna and Miller 2004). Breastfeeding does not need to be stopped for the examination; ^99mTc radiopharmaceuticals are preferred in this setting (Hesse et al. 2005). In males, gynecomastia may be evident (Fig. 6.3) and is often associated with underlying liver disease or associated with hormonal therapy or medical therapy for congestive heart failure (e.g., spironolactone).

^99mTc sestamibi has been long used clinically to evaluate the breast for malignancy (Taillefer et al. 1995, 1998; Waxman 1997). Breast-specific gamma imaging (BSGI) remains under active investigation as a molecular approach adjunctive to mammography, ultrasonography, and magnetic resonance imaging, particularly in mammographically dense breasts (Holbrook and Newel 2015). Thus, the differential diagnosis for focal increased uptake in the breasts includes primary, metastatic, or recurrent breast malignancy, particularly if it is unilateral and intensely avid for ²⁰¹Tl chloride and ^99mTc sestamibi (Fig. 6.4) (Arbab et al. 1995; Chamarthy and Travin 2010; García-Talavera et al. 2013; Hendel et al. 1999; Mlikotic and Mishkin 2000; Shih et al. 2002; Williams et al. 2003). The rest raw acquisition might be more revealing and should be reviewed, ideally with a whole-field-of-view reconstruction for three-dimensional characterization of a suspected lesion (Seo et al. 2005). The written report should include wording along the lines of: