Yiannis Kyriakou PhD, Presenter: Nothing to Disclose

Michael Meyer, Abstract Co-Author: Nothing to Disclose

Marc Kachelriess PhD, Abstract Co-Author: Nothing to Disclose

Willi A. Kalender PhD, Abstract Co-Author: Consultant, Siemens AG Founder, VAMP GmbH Scientific Advisor, VAMP GmbH Shareholder, VAMP GmbH

To combine Monte Carlo (MC)-based object-specific scatter calculations with empirical methods for the reduction of cupping and streaks in FD-CT.

Pure MC-based methods for scatter correction need several iterations for good results due to the insufficient image quality of the initial voxel-volume used for the calculations. We applied an empirical cupping correction (ECC) which uses a set of pre-calculated polynomial correction coefficients for cupping removal. While the ECC suppresses both beam hardening and scatter effects for homogeneous water-like phantoms, it is deficient for inhomogeneous objects containing e.g. bone. However, the ECC-corrected raw data were used to improve the initial reconstructed volume which was used for the MC scatter estimation. Detector elements were binned and the angular increment between the estimated projections was enlarged to speed up the calculation. After spatial and angular interpolation, the scatter estimates were subtracted from the original data and were combined with a second set of ECC coefficients to remove remaining beam hardening-induced cupping. The correction method was applied to simulated head and body datasets of patient CT scans for which scatter was generated by MC calculations. For comparison, reference reconstructions of scatter and beam-hardening-free projections were generated. The root-mean-square error (RMSE) between both the corrected and uncorrected images relative to the reference was calculated. The method was also applied to anthropomorphic phantom data measured on a C-arm FD-CT system (Artis zeego, Siemens Healthcare, Forchheim, Germany) using a large flat-detector of 40x30cm².

Use of the proposed correction method on the simulated data provided an RMSE of 6-18% as compared to the ideal data, whereas without correction an RMSE of 40-60% was registered depending on phantom and setup. The number of iterations for the scatter correction was reduced from 4 to 1 when compared to a pure iterative MC approach data for equivalent artifact reduction (20 s per iteration on a standard PC). The correction of the measured images led to an increase of contrast and a general reduction of cupping and streaks.

The proposed method provides a fast and object-specific correction of inhomogeneities in FD-CT.

Reduction of cupping and scatter artifacts improves image quality and improves quantitative evaluation.

Kyriakou, Y, Meyer, M, Kachelriess, M, Kalender, W, Combination of an Empirical Cupping Correction and Monte Carlo (MC) Methods for Simultaneous Correction of Cupping and Scatter Artifacts for Flat-Detector CT (FD-CT).  Radiological Society of North America 2008 Scientific Assembly and Annual Meeting, February 18 - February 20, 2008 ,Chicago IL. http://archive.rsna.org/2008/6011336.html