3. Female patient is pregnant or nursing. Exclusion of the possibility of pregnancy is made by one of the following: 1) woman is physiologically post menopausal (cessation of menses for more than 2 years), 2) woman is surgically sterile (has had a documented bilateral oophorectomy and/or documented hysterectomy, or 3) if the woman is of childbearing potential, a urine pregnancy test performed within 24 hours immediately prior to administration of [18F]FES has to be negative and the women is advised to apply contraceptive measures during her participation in this study