A system for breast region determination, the system comprising: an image processing module configured to obtain a breast image of an object that is acquired by an imaging device; and determine a projection curve based on the breast image by determining a plurality of sum values each of which is a sum of pixel values of a row of pixels in a binary image of the breast image, the row of pixels being arranged along a direction perpendicular to a chest-wall side and between the chest-wall side and a side of the binary image opposite to the chest-wall side; a curve processing module configured to determine a first valley point and a second valley point of the projection curve based on a shape of the projection curve, wherein the first valley point and the second valley point correspond to locations at a junction of a breast and a chest wall of the object in the breast image; and determine a peak point of the projection curve between the first valley point and the second valley point of the projection curve, wherein the peak point represents a mammilla of the breast; and a location processing module configured to determine a first valley location, a second valley location, and a peak location in the breast image that correspond to the first valley point, the second valley point, and the peak point of the projection curve respectively; and determine a breast region in the breast image by connecting the first valley location, the second valley location, and the peak location. an image processing module configured to obtain a breast image of an object that is acquired by an imaging device; and determine a projection curve based on the breast image by determining a plurality of sum values each of which is a sum of pixel values of a row of pixels in a binary image of the breast image, the row of pixels being arranged along a direction perpendicular to a chest-wall side and between the chest-wall side and a side of the binary image opposite to the chest-wall side; obtain a breast image of an object that is acquired by an imaging device; and determine a projection curve based on the breast image by determining a plurality of sum values each of which is a sum of pixel values of a row of pixels in a binary image of the breast image, the row of pixels being arranged along a direction perpendicular to a chest-wall side and between the chest-wall side and a side of the binary image opposite to the chest-wall side; a curve processing module configured to determine a first valley point and a second valley point of the projection curve based on a shape of the projection curve, wherein the first valley point and the second valley point correspond to locations at a junction of a breast and a chest wall of the object in the breast image; and determine a peak point of the projection curve between the first valley point and the second valley point of the projection curve, wherein the peak point represents a mammilla of the breast; and determine a first valley point and a second valley point of the projection curve based on a shape of the projection curve, wherein the first valley point and the second valley point correspond to locations at a junction of a breast and a chest wall of the object in the breast image; and determine a peak point of the projection curve between the first valley point and the second valley point of the projection curve, wherein the peak point represents a mammilla of the breast; and a location processing module configured to determine a first valley location, a second valley location, and a peak location in the breast image that correspond to the first valley point, the second valley point, and the peak point of the projection curve respectively; and determine a breast region in the breast image by connecting the first valley location, the second valley location, and the peak location. determine a first valley location, a second valley location, and a peak location in the breast image that correspond to the first valley point, the second valley point, and the peak point of the projection curve respectively; and determine a breast region in the breast image by connecting the first valley location, the second valley location, and the peak location.