In cone-beam CT, x-ray projection imagesof a patient are measured from different angular positions. In order to reconstruct artifact-free tomographic volumes with high spatial resolution,the exact acquisition geometrymust be known and taken into accountin the image reconstruction process. Due to various sources of error, the accuracy of thegeometry may be decreased (misaligned). These geometry misalignmentsusually 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...

An automatic geometry alignment correction method that is based on comparing redundant rays (line integrals) was implemented. The proposed method is capable of correcting alignment errors regarding horizontal detector offsets u0, rotation axis tilts a, and rotation axis skews b. Assuming a full circle scan, many rays within the plane of the source rotation is measured twice. The L2 norm ofthe measured line integralsof a ray p and its complementary rayq is used to quantify the geometry parameter quality: c = ||p - q||2. Typically,...

The proposed method was capable to fully correct individual misalignments of the horizontal detector offset u0and the axis skew b for all datasets. The full correction of the axis tilt a was possible for three of the five datasets. Fig. 1 shows the central slice of the thorax phantom with a misaligned horizontal detector offset.Fig. 2 shows the same slice after applying the proposed misalignment correction method. Fig. 3 shows a detail of the central slice of the head phantom with a misaligned axis skew.Fig....

A misalignment correction method based on redundantly measured information was successfully applied to reduce image artifacts in cone-beam CT. While the fully automatic correction of horizontal detector shifts and axis skews was successful, an extension of the proposed method is needed for the reliable correction of axis tilts.

D. Panetta, N. Belcari, A. Del Guerra, and S. Moehrs, An optimization-based method for geometrical calibration in cone-beam CT without dedicated phantoms, Phys. Med. Biol., vol. 53, pp. 3841-3861, 2008 A. Kingston, A. Sakellariou, T. Varslot, G. Myers, and A. Sheppard, Reliable automatic alignment of tomographic projection data by passive auto-focus, Medical Physics, vol. 38, no. 9, pp. 4934-4945, 2011 Y. Kyriakou, R. Lapp, L. Hillebrand, D. Ertel, and W. A. Kalender, Simultaneous misalignment correction for approximate circular cone-beam computed tomography, Phys. Med. Biol., vol....

Matthias Elter PhD, Siemens AG, Healthcare Sector, Erlangen, Germany, [email protected] Thomas Lang, Siemens AG, Healthcare Sector,Erlangen, Germany, [email protected] Nicole Maass PhD, Siemens AG, Healthcare Sector,Erlangen, Germany, [email protected]