Keywords:
Radiation physics, Computer applications, Cone beam CT, CT-Angiography, Physics, Computer Applications-3D, Image guided radiotherapy, Artifacts
Authors:
M. Elter, T. D. O. Lang, N. Maaß; Erlangen/DE
DOI:
10.1594/ecr2013/C-0496
Purpose
In cone-beam CT,
x-ray projection images of a patient are measured from different angular positions.
In order to reconstruct artifact-free tomographic volumes with high spatial resolution, the exact acquisition geometry must be known and taken into account in the image reconstruction process.
Due to various sources of error,
the accuracy of the geometry may be decreased (misaligned).
These geometry misalignments usually lead to image artifacts and reduced spatial resolution in reconstructed slices and volumes.
Global misalignments,
such as a tilted rotation axis,
affect all projections of a dataset.
In circular geometry, six global parameters can be identified that significantly influence the reconstruction image quality.
These are in the order of their importance: u0,b,a,c,R,D.
Recently algorithmic methods for the estimation of global geometry parameters that do not require scanning a dedicated calibration phantom or inserting image markers have been proposed.
In reference (1) a cost function that is based on redundantly measured raw-data is formulated as a function of geometry parameters.
In an alternative method (2), a cost function based on a sharpness metric in the domain of the reconstructed volume is formulated.
Other approaches based on volume-domain cost functions have been proposed in references (3-5).
The purpose of this study is to implement and evaluate a misalignment correction method,
similar to the one proposed in (1) that is based on a raw-data domain cost function with regard to its applicability and robustness for medical cone-beam CT.