Harald Schoendube PhD, Abstract Co-Author: Employee, Siemens AG Stockholder, Siemens AG

Thomas Allmendinger, Abstract Co-Author: Employee, Siemens AG

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

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

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

To present and evaluate a new algorithm to enhance temporal resolution in CT beyond the short-scan limit by making use of a histogram constraint.

A minimum scan angle of 180° plus fan angle is needed to acquire complete data for reconstructing an image. Conventionally, this means that a temporal resolution of half the gantry rotation time is achievable in the isocenter and that an enhancement of temporal resolution can only be accomplished by a faster gantry rotation or by using a dual-source system. In this work we pursue a different approach, namely employing an iterative algorithm to reconstruct images from less than 180° of projections and using a histogram constraint to prevent the occurrence of limited-angle artifacts. The method is fundamentally different from previously published approaches using prior images and TV minimization. We evaluate the proposed technique with an experiment designed to provide reliable data regarding the temporal resolution of CT images using measured data of a cardiac phantom. We furthermore evaluate our method using clinical data from dual source cardiac scans with a relatively slow rotation time of 0.5s. From these data we obtain conventionally reconstructed images with a temporal resolution of 130ms by using the dual-source data and images with a temporal resolution of 250ms when only using a single-source subset. We then reconstruct images using our proposed algorithm from the single-source subset yielding a temporal resolution of about 200ms and evaluate them against the conventionally reconstructed single-source and dual-source images.  

The proposed method yields good results, both with phantom and clinical data. Our evaluations show that an enhancement of temporal resolution to a value equivalent to about 120°-135° of projections is viable. Furthermore, by employing motion detection, a substantial noise reduction can be achieved in those parts of the image where no motion occurs.

Using our proposed method, an enhancement of temporal resolution in CT images by about 30% is possible. Furthermore, an optimization of dose usage can be achieved by use of a motion detection system.

Enhancing the temporal resolution of CT images is of high clinical relevance especially for cardiac imaging; the presented results are directly applicable to this modality.

Schoendube, H, Allmendinger, T, Stierstorfer, K, Bruder, H, Flohr, T, Evaluation of an Algorithmic Method to Enhance Temporal 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/2011/11011573.html