Streak-like artifact reduction control in CT reconstruction

Inhomogeneous noise distribution may result in streak-like artifacts in reconstructed CT images. These streak-like artifacts can be overcome with an adaptive filter applied locally to some of the data points in the attenuation profile, those data points for which the attenuation is high and the signal is low. However, such a local filter might cause new smearing artifacts if the filter is applied over edges in the scanned object. We suggest adding to the adaptive filter a control mechanism aimed to avoid the creation of such new artifacts. With this control mechanism, every modification suggested by the adaptive filter is examined and if it is estimated to be the result of a real gradient in the scanned object, the data is modified only moderately or not at all. Such a control mechanism can be added to different adaptive filters. We have been working with an adaptive filter based on estimation of photon noise. The control mechanism in our case limits the modification allowed by the adaptive filter to the size of noise expected for that data point. Experiments with clinical studies show that images produced with the new control mechanism indeed reduce creation of new smearing artifacts of bones and contrast material.