X-ray imaging systems and methods for exposure control in three-dimensional X-ray imaging include acquiring at least one image with an X-ray emitter and an X-ray receiver. At least one physical characteristic of the object to be imaged is determined from the at least one image. At least one exposure parameter value based is determined based upon the at least one physical characteristic of the object to be imaged. The X-ray emitter and X-ray receiver acquire a plurality of projection images about the object to be imaged using at least one exposure parameter value. A three-dimensional X-ray image is reconstructed from the plurality of projection images.