If using only the information of one single energy scan, there are two types of corrections. In contrast, more complex artifacts like streaks between dense objects need other techniques of correction. They correct the hardening of the spectrum during the penetration of the measured object only for the major tissue class. To correct for a general cupping, methods like water precorrection exist. This leads to cupping and beam hardening artifacts inside the reconstructed volume. Purpose: The polychromatic nature of the x-ray beams and their effects on the reconstructed image are often disregarded during standard image reconstruction. The consequences for the quantitative interpretation of CT numbers for clinical diagnoses are =, number = , We demonstrated that, at least in the pelvis, scatter is a more significant source of error than beam hardening and that improved scatter correction algorithms are needed. Nevertheless, it still gave substantial improvement in the pelvic scan. The algorithm worked well on the smaller phantoms but was less successful for the larger objects. A simple model with constant scatter background leads to a correction algorithm which was tested on several phantoms and one human pelvis. The presence of scatter induced streaks were demonstrated experimentally on both a third and a fourth-generation CT scanner using an appropriate water-equivalent phantom. It is shown that scatter effects predominate over beam spectrum hardening effects for large body parts, and that the artifact propensity is a direct function of the scatter-to-primary ratio. It is shown that scatter induces nonlinear errors in the measurement of attenuation values which can lead to cupping, streaks, and CT number inaccuracies. The effects of detection of scattered radiation in x-ray transmission CT are studied both theoretically and experimentally.

Scatter radiation radiology