Evaluation of a novel CT image reconstruction algorithm with enhanced temporal resolution

We present an evaluation of a novel algorithm that is designed to enhance temporal resolution in CT beyond the short-scan limit by making use of a histogram constraint. A minimum scan angle of 180 degrees 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 degrees 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. Furthermore, motion detection is used to enhance dose usage in those parts of the image where temporal resolution is not critical. We evaluate the technique with patient and phantom scans as well as using simulated data. The proposed method yields good results and image quality, both with simulated and with clinical data. Our evaluations show that an enhancement of temporal resolution to a value equivalent to about 120 degrees of projections is viable, which corresponds to an enhancement of temporal resolution by about 30%. Furthermore, by employing motion detection, a substantial noise reduction can be achieved in those parts of the image where no motion occurs.