A diagnostic computed tomographic imaging apparatus, comprises a patient support structure including a tabletop to support a patient in front-down, prone position. The tabletop includes an opening to permit a breast of the patient to be vertically pendant below the tabletop. A scanning mechanism is disposed below the opening and orbitable about the breast pendent through the opening to obtain perimeter data and image reconstruction data of the breast. The scanning mechanism rotates about an axis of rotation transverse to the tabletop. One of the tabletop and scanning mechanism is movable in x-y axes to center the breast about the axis of rotation.