1. A breast imaging apparatus, comprising: a locator for positioning a patient's breast within a predetermined frame of reference having a predetermined axis extending away from a boundary plane of the predetermined frame of reference, wherein an axis of a patient's breast that extends from a patient chest wall through a patient's breast nipple is alignable with said predetermined axis for imaging; an imaging beam source for transmitting an imaging beam though said predetermined frame of reference; an imaging signal detector for receiving said imaging beam and providing an output signal in response thereto, wherein said imaging beam source and said imaging signal detector are each independently moveable relative to said predetermined frame of reference and are independently moveable relative to one another, wherein said apparatus is operable so that said output signal comprises projection image data corresponding with a predetermined angular range of projection views of a patient's breast, and wherein said imaging signal detector comprises: an array of detector elements, wherein during operation an active array of detector elements is scanned across a region of interest within said predetermined frame of reference, said active array having a length defined by at least one column of aligned detector elements extending parallel to said predetermined axis of said predetermined frame of reference and having a width defined by at least one detector element extending in a direction orthogonal to said length, wherein said width of the active array is less than a width of a patient's breast located within said predetermined frame of reference; and, a processor for computed tomography processing said projection image data to provide a reconstructed image.