An x-ray collimator comprising: a substrate (10) containing a plurality of holes (30), each hole being frustoconical (40) at one end and tubular (50) at the other end for use in an x-ray imaging system, whereby the x-ray collimator is aligned with a two-dimensional array of x-ray sources (70) and a two-dimensional x-ray sensor (130), whereby x-ray photons from the x-ray sources pass through the collimator holes and emerge as a beam of x-ray photons in a narrow angle cone which pass through the subject (110) being imaged, positioned between the output holes of the collimator and the x-ray sensor.
