123 research outputs found
Research Status and Prospect for CT Imaging
Computed tomography (CT) is a very valuable imaging method and plays an important role in clinical diagnosis. As people pay more and more attention to radiation doses these years, decreasing CT radiation dose without affecting image quality is a hot direction for research of medical imaging in recent years. This chapter introduces the research status of low-dose technology from following aspects: low-dose scan implementation, reconstruction methods and image processing methods. Furthermore, other technologies related to the development tendency of CT, such as automatic tube current modulation technology, rapid peak kilovoltage (kVp) switching technology, dual-source CT technology and Nano-CT, are also summarized. Finally, the future research prospect are discussed and analyzed
Comparison of Quadratic- and Median-Based Roughness Penalties for Penalized-Likelihood Sinogram Restoration in Computed Tomography
We have compared the performance of two different penalty choices
for a penalized-likelihood sinogram-restoration strategy we have
been developing. One is a quadratic penalty we have employed
previously and the other is a new median-based penalty. We
compared the approaches to a noniterative adaptive filter that
loosely but not explicitly models data statistics. We found that
the two approaches produced similar resolution-variance tradeoffs
to each other and that they outperformed the adaptive filter in
the low-dose regime, which suggests that the particular choice of
penalty in our approach may be less important than the fact that
we are explicitly modeling data statistics at all. Since the
quadratic penalty allows for derivation of an algorithm that is
guaranteed to monotonically increase the penalized-likelihood
objective function, we find it to be preferable to the median-based penalty
Stage-by-stage Wavelet Optimization Refinement Diffusion Model for Sparse-View CT Reconstruction
Diffusion models have emerged as potential tools to tackle the challenge of
sparse-view CT reconstruction, displaying superior performance compared to
conventional methods. Nevertheless, these prevailing diffusion models
predominantly focus on the sinogram or image domains, which can lead to
instability during model training, potentially culminating in convergence
towards local minimal solutions. The wavelet trans-form serves to disentangle
image contents and features into distinct frequency-component bands at varying
scales, adeptly capturing diverse directional structures. Employing the Wavelet
transform as a guiding sparsity prior significantly enhances the robustness of
diffusion models. In this study, we present an innovative approach named the
Stage-by-stage Wavelet Optimization Refinement Diffusion (SWORD) model for
sparse-view CT reconstruction. Specifically, we establish a unified
mathematical model integrating low-frequency and high-frequency generative
models, achieving the solution with optimization procedure. Furthermore, we
perform the low-frequency and high-frequency generative models on wavelet's
decomposed components rather than sinogram or image domains, ensuring the
stability of model training. Our method rooted in established optimization
theory, comprising three distinct stages, including low-frequency generation,
high-frequency refinement and domain transform. Our experimental results
demonstrate that the proposed method outperforms existing state-of-the-art
methods both quantitatively and qualitatively
Iterative CT reconstruction from few projections for the nondestructive post irradiation examination of nuclear fuel assemblies
The core components (e.g. fuel assemblies, spacer grids, control rods) of the nuclear reactors encounter harsh environment due to high temperature, physical stress, and a tremendous level of radiation. The integrity of these elements is crucial for safe operation of the nuclear power plants. The Post Irradiation Examination (PIE) can reveal information about the integrity of the elements during normal operations and off‐normal events. Computed tomography (CT) is a tool for evaluating the structural integrity of elements non-destructively. CT requires many projections to be acquired from different view angles after which a mathematical algorithm is adopted for reconstruction. Obtaining many projections is laborious and expensive in nuclear industries. Reconstructions from a small number of projections are explored to achieve faster and cost-efficient PIE. Classical reconstruction algorithms (e.g. filtered back projection) cannot offer stable reconstructions from few projections and create severe streaking artifacts. In this thesis, conventional algorithms are reviewed, and new algorithms are developed for reconstructions of the nuclear fuel assemblies using few projections. CT reconstruction from few projections falls into two categories: the sparse-view CT and the limited-angle CT or tomosynthesis. Iterative reconstruction algorithms are developed for both cases in the field of compressed sensing (CS). The performance of the algorithms is assessed using simulated projections and validated through real projections. The thesis also describes the systematic strategy towards establishing the conditions of reconstructions and finds the optimal imaging parameters for reconstructions of the fuel assemblies from few projections. --Abstract, page iii
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