Dual-energy CT (DECT) provides additional material-based contrast using spectral information. The realization of DECT using a rotation-to-rotation kVp switching may suffer from structure misalignment due to patient’s motion and requires deformable image registration (DIR) between the two kVp images. Recent studies in DIR has highlighted deep-learning-based methods which can achieve superior registration accuracy with reasonable computational time. However, current deep-learning-based DIR methods may eliminate important anatomical features or hallucinate faked structures. The lack of interpretability complicates the robustness verification. Alternatively, recent studies have introduced the algorithm unrolling method that provides a concrete and systematic connection between model-based iterative methods and data-driven methods. In this work, we present an unsupervised Model-Based deep Unrolling Registration Network (MBURegNet) for DIR in DECT. MBURegNet comprises a sequence of stacked update blocks to unroll the Large Deformation Diffeomorphic Metric Mapping method, where each block samples the velocity field that follows the diffeomorphism physics. Preliminary studies using clinical data has shown that the proposed network can achieve superior performance improvement compared to the baseline deep-learning-based method, as evidenced by both qualitative and quantitative analyses. Additionally, the network can generate a sequence of intermediate images connecting the initial and final motion states, effectively illustrating the continuous flow of diffeomorphisms.
Multiple CT vendors have released clinical multi-detector (MD) computed tomography (CT) systems with 16cm coverage. Axial CT for voxels outside the acquisition plane does not satisfy a fundamental completeness condition, which leads to so called cone-beam artifacts. This paper revisits the iterative filtered back-projection (FBP) algorithm from 2008 and analyzes it in the context of Brerman iterations. Also, we propose a one application of this algorithm along with a recently published filtering orthogonal to the acquisition plane as a pragmatic way to considerably reduce the cone-beam artifacts in axial CT scans with high coverage.
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