Johan Sunnegardh, Abstract Co-Author: Employee, Siemens AG

Rainer Raupach PhD, Abstract Co-Author: Employee, Siemens AG

Herbert K. Bruder PhD, Abstract Co-Author: Employee, Siemens AG

Karl Stierstorfer PhD, Abstract Co-Author: Employee, Siemens AG

Thomas G. Flohr PhD, Presenter: Employee, Siemens AG

In CT, due to the sizes of x-ray focus and the interpolations present in all conventional reconstruction algorithms, the obtained cross-plane (transaxial) resolution is lower than the theoretical maximum as defined by the detector aperture. Rawdata-based iterative reconstruction has been shown to significantly improve the resolution. We present a new, computationally more efficient, image-based approach, and compare it to the established rawdata-based approach.

Spatial extent and cross-plane response functions of focus and detector elements, as well as interpolation functions, determine the cross-plane resolution of a CT system. Based on accurate models of these functions, we use penalized weighted least squares methods to optimize a resolution improvement filter, which is applied to images reconstructed with a very fine slice increment. The increased noise can be reduced by non-linear image processing techniques. For z-flying focal spot scanning modes, this new method is compared with rawdata-based iterative reconstruction modelling the cross-plane response function in the forward projector.

Based on simulations and phantom scans, iso-center slice sensitivity profiles, noise and visual appearance are studied for different configurations of the image-based method and for the rawdata-based iterative reconstruction. In terms of these image quality measures, the image-based approach produces results equivalent to those of the rawdata-based method. Furthermore, it is shown how the new method can be configured to reduce edge overshoots normally caused by resolution improvement methods.

For common scanning modes, the proposed image-based method provides the same resolution improvement as the rawdata-based method. It is also simpler to configure to avoid artifacts commonly associated with resolution improvement.

It is possible to increase the transaxial resolution in CT close to the theoretical limit without overly increasing reconstruction time.

Sunnegardh, J, Raupach, R, Bruder, H, Stierstorfer, K, Flohr, T, Comparison of Iterative and Analytical Model-based Approaches for Improvement of Cross-Plane Resolution in CT.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11034583.html