Breast cancer patients who diagnosed by core needle biopsy or excisional biopsy underwent CT scan to locate the sentinel lymph node (SLN) before SLN biopsy (SLNB) at the same day of surgery. When CT examination performed, those patients were in supine position, with the arms stretched upward but bent at the elbow with the hands at the side of the cranium which similar to the surgical position. After local anesthesia, 2mL of iopamidol was injected subcutaneously to the peritumoral and peri-areolar areas followed by gentle massage for about 1 minute. Contiguous 2-mm-thick CT images that included the breast and axilla were obtained prior to administration of the contrast agent. After 3D CT reconstruction, the SLN was identified as the most inferiorly visible nodule in the axilla connected to the lymphatic vessel on the CT imaging monitor. A professional intervention doctor punctured the defined lymph node guided by the CT monitor using the Breast Lesion Localization Needles (interv). The needle would stay in the patient's axilla until the surgery. All the lymph nodes including the CT defined one and which marked by methylene blue dye or 99mTc-sulfur colloid tracers were removed, which then would be tested by touch imprint cytology for the intraoperative diagnosis. Patients who had positive SLN would receive axillary dissection. The investigators evaluated the new method by comparing lymph nodes defined by CT and traditional ways.