  In X-ray CT scan with metallic objects, it is known that direct application
of the filtered back-projection (FBP) formula leads to streaking artifacts in
the reconstruction. These are characterized mathematically in terms of wave
front sets in [13]. In this work, we give a quantitative microlocal analysis of
such artifacts. We consider metal regions with strictly convex smooth
boundaries and show that the streaking artifacts are conormal distributions to
straight lines tangential to at least two boundary curves. For metal regions
with piecewise smooth boundaries, we analyze the streaking artifacts especially
due to the corner points. Finally, we study the reduction of the artifacts
using appropriate filters.
