Computer assisted radiology and surgeryProjection Extension for Region Of Interest Imaging in Cone-Beam CT1
Section snippets
Overview of the method
The method for correction of truncation errors during reconstruction consists of the following steps. First, a preliminary reconstruction of the ROI is performed using the standard elliptical projection extension method similar to the one described in (3) in order to approximatively compensate for the truncation artifacts. In essence, each row of each truncated projection is extended by fitting an elliptical arc to both of its ends. The lateral extent of the elliptical arc is controlled by an
Differing Beam Quality
In cases where the reference volume has been acquired with a different modality, e.g. CT, it usually has also been acquired with a different X-ray spectrum. Due to the energy dependence of the attenuation coefficient, different line integral values are thus obtained for the forward projection of the reference volume and for the measured ROI projections. To investigate the effect of differences in beam quality, the projections of the reference volume have been simulated with a mono-energetic
Discussion
In this work, we have presented an accurate method for compensation of truncation artifacts in cone-beam CT. The method works by laterally extending truncated projections using forward-projected data of an a priori available truncation-free reference volume. For the practical application of this technique it has been shown that adequate gray level transformations prior to reconstruction are essential to compensate for differing gray level scales of both data sources caused by, e.g., differing
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