An x-ray computed tomography system (14) includes a gantry (15), a plurality of elements (18), and one or more processors (28). The gantry (15) moves to different orientations and generates x-ray data which includes image projection data at a plurality of the orientations. The plurality of elements (18) connect to the gantry and cause x-ray attenuation of the generated projection data. The one or more processors (28) are programmed to receive (60) the generated x-ray data and decompose (62) the received image projection data into indications of relative positions of the plurality of elements at different orientations of the gantry.