1. An imaging system, comprising: a portable source of radiation; a portable detector operable to detect the radiation from the portable source, wherein the detector is adapted to move independently of the portable source in all degrees of freedom; and an alignment system comprising a plurality of transmitters disposed on an anti-scatter grid disposed over the portable detector, wherein the alignment system is operable to establish an orientation of the portable detector relative to the portable source based on signals from the plurality of transmitters.