A detection apparatus for detecting high energy radiation, preferably for detecting gamma radiation, coming from a source of high energy radiation in a detection volume, e.g. from one or more particles emitting high energy radiation. The apparatus comprises at least one detection surface configured to convert incident high energy radiation into a detection signal, and a collimator system comprising at least three collimator slits. Each collimator slit is arranged to project high energy radiation coming from a respective slit field of view of said detection volume onto said detection surface. At least two of said collimator slits extend in non-parallel directions and the respective slit fields of view of said at least two non-parallel collimator slits and the slit field of view of any other of said at least three collimator slits overlap and define a common detection volume of the detection apparatus.