1. An imaging system comprising: a gantry; a plurality of imaging detector units, each detector unit comprising a detector arm installed in the gantry and a detector head; wherein at least one of the detector heads is movable such that its angle can be altered with respect to its detector arm; a controller in communication with the plurality of detector units, configured to control the angle of the at least one detector head; and wherein if the controller detects an obstruction in a field of view a detector head, the controller updates a system matrix to include obstruction information related to the obstruction.