Abstract.
In cardiac CT imaging an optimal phase determination is a prerequisite for good image quality. The aim of this work is to develop an alternative gating strategy in optimizing cardiac image reconstruction by automatically defining the optimum gating phase of the heart independently from patient-patient and cycle-cycle variability.
Automatic optimum phase detection introduced by Phillips Research laboratories is reproduced for this purpose. The method successfully shows motion pattern of the heart, and delivers the systole-diastole phase directly from a motion map. However in coronary CT angiography the domain of Cardiac CT imaging, the method is not accurate enough. Motion of the arteries are overshadowed by the chamber motion, thus the real motion pattern of arteries are not presented well.
Defining subset voxel containing mainly the coronary arteries will expand the functionality of the algorithm. Instead of the whole axial slices, the motion map is derived from the subset voxels. Additional histogram HU weighting function is also used in order to focus the motion calculation on pixels containing contrast media.
The algorithm is validated with three patient data from University of Tübingen measured with a 16 slices scanner. The right coronaryartery is analyzed and the cycle-dependent local phases are determined. Comparing image reconstructed with the proposed algorithm and images reconstructed with conventional method, shows the improvement in the image quality and demonstrates the benefit ofthe automatic method. The coronary artery is shown with high contrast and in good continuity with reduced motion artifact. Nevertheless, its limitation to eliminate residual step artifact is one important topic, which needs to be investigated in the further work.
Keyword: Cardiac CT Imaging, gating strategies, Motion Map, optimum phase selection
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