  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.
