Polychromatic streak artifacts in computed tomography images.

A series of artifacts in computed tomography (CT) images, consisting of streaks coming off edges and flares surrounding the object being scanned, is shown to be due to polychromaticity of the X-ray beam. These artifacts are seldom seen on conventional CT brain scans. They are helpful in understanding artifacts such as those seen around the petrous bone of the skull. Following this, a comparison is made between "single energy" and "dual energy" correction schemes for poly-artifacts. The theoretical assumptions underlying either method are analyzed, and the importance of these concepts in dual energy reconstructions is stressed. A new test phantom is suggested to evaluate different poly-correction schemes. All the simulated projection data in this study are noise free and are reconstructed using an industrial convolution-back projection technique. In addition, reconstructions are shown of the phantom using real data taken with and without a water bag path length compensator.