Artifact-less Coded Aperture Imaging in the X-ray Band with Multiple Different Random Patterns.

The coded aperture imaging technique is a useful method of X-ray imaging in observational astrophysics. However, the presence of imaging noise or so-called artifacts in a decoded image is a drawback of this method. We propose a new coded aperture imaging method using multiple different random patterns for significantly reducing the image artifacts. This aperture mask contains multiple different patterns each of which generates a different artifact distribution in its decoded image. By summing all decoded images of the different patterns, the artifact distributions are cancelled out, and we obtain a remarkably accurate image. We demonstrate this concept with imaging experiments of a monochromatic 16 keV hard X-ray beam at the synchrotron photon facility SPring-8, using the combination of a CMOS image sensor and an aperture mask that has four different random patterns composed of holes with a diameter of 27 um and a separation of 39 um. The entire imaging system is installed in a 25 cm-long compact size, and achieves an angular resolution of < 30'' (full width at half maximum). In addition, we show by Monte Carlo simulation that the artifacts can be reduced more effectively if the number of different patterns increases to 8 or 16.