Institutional review board approval from the North Shore University Health System/Evanston, IL, USA, was obtained and all participants signed a written consent before the data collection. Ultrasound examinations were performed with a GE Logic-E9 ultrasound machine (General Electric, Milwaukee, WI USA) integrated with the automated breast ultrasound system BVN Model G-1000. Six women aged between 26 and 57 years old and with known benign or probably benign masses measuring 0.5-2 cm in maximum dimensions were scanned by two radiologists with at least five years of experience in breast imaging. Four masses were found in the lateral quadrants and 2 masses in the inner quadrants. Breast cup size was DD and D in 4 patients; C and B in the other 2 patients. Each radiologist performed a separate exam and obtained images of the target breast mass in supine position with the ultrasound probe in one reference position, orthogonal probe orientation to the reference position and the probe tilted at approximately -25, and +25 degrees relative to the probe axis angle to the coronal plane in the reference position and the image in orthogonal orientation to the reference image, for a total of 6 images (Fig 1). The above sequence of images was repeated with the patient rotated in the semi oblique position on the exam table. Measurements of the target mass were also manually recorded in accordance with the ACR recommendations. The automated mapping system provided the clock face position, distance to nipple, angles of body rotation on table values, in addition the probe axis angles the x,y,z coordinates of target and landmarks in the spatial frame (Fig.2). The automated clock face position and distance to nipple coordinates are easier to compare with the standard manual annotations, which use same measurement format. The x,y,z coordinates and probe axis angles allow for the precise measurements of displacements. The 3D and 2D lesion displacements between the examiners were calculated for the coordinates of the center of the target mass (MD) and the coordinates of the center of the probe (PCD). The 3D displacements were calculated as the distance between the position of a target in the second image and the position coordinates of same target obtained in the first image. The 2D displacements represent the projection of the 3D displacement line segment in the coronal plane. All sessions were video recorded and scan times obtained from the time stamps. A total of 656 image pairs were analyzed. To examine the relationship between mass center and probe center coordinates Spearman’s rho was used. Partial correlation tests including variables associated with probe and patient position were performed to analyze correlations between mass center and probe center coordinates controlling for the potential confounding impact of these factors. All statistical tests were two-sided and the level of significance was set at p <0.05. Statistical analysis was conducted using SAS software package version 9.4 (SAS Institute Inc., Cary, NC) and STATA version 13.0 (StataCorp, College Station, Texas, USA)