1. A system for providing an image of a region of an object, the region including a plurality of object elements, and the region defining a longitudinal axis, the system comprising: a source of radiation operable for interrogating the object with a first radiation signal having energy within an energy passband that ranges from approximately 30 keV to approximately 69.5 keV; a coded aperture operable for modulating a second radiation signal received from the object, the second radiation signal being based on the first radiation signal; a detector comprising a two-dimensional arrangement of pixels, the detector operable for detecting a modulated image based on the modulated second signal; and a processor operable for computing an estimate of the composition of the region based on the modulated image and a longitudinal forward model of the system.