Abstract: Body structures into which a gamma-emitting isotope has been introduced are investigated using an imaging system comprising in sequence a collimator, a first detector, a filter, and a second detector. The first detector is partially transparent to the emerging photons and the filter is adapted to have an absorption edge energy fractionally less than the energy of the radioactive isotope source. The first detector produces an image of both scattered and non-scattered photons and the second detector simultaneously produces an image of only the scattered photons. The two images can be manipulated to produce an image due only to non-scattered photons which is the image of interest.