2,769 research outputs found
Recent Progress in Image Deblurring
This paper comprehensively reviews the recent development of image
deblurring, including non-blind/blind, spatially invariant/variant deblurring
techniques. Indeed, these techniques share the same objective of inferring a
latent sharp image from one or several corresponding blurry images, while the
blind deblurring techniques are also required to derive an accurate blur
kernel. Considering the critical role of image restoration in modern imaging
systems to provide high-quality images under complex environments such as
motion, undesirable lighting conditions, and imperfect system components, image
deblurring has attracted growing attention in recent years. From the viewpoint
of how to handle the ill-posedness which is a crucial issue in deblurring
tasks, existing methods can be grouped into five categories: Bayesian inference
framework, variational methods, sparse representation-based methods,
homography-based modeling, and region-based methods. In spite of achieving a
certain level of development, image deblurring, especially the blind case, is
limited in its success by complex application conditions which make the blur
kernel hard to obtain and be spatially variant. We provide a holistic
understanding and deep insight into image deblurring in this review. An
analysis of the empirical evidence for representative methods, practical
issues, as well as a discussion of promising future directions are also
presented.Comment: 53 pages, 17 figure
Free-Breathing Myocardial T1 Mapping using Inversion-Recovery Radial FLASH and Motion-Resolved Model-Based Reconstruction
Purpose: To develop a free-breathing myocardial T1 mapping technique using
inversion-recovery (IR) radial fast low-angle shot (FLASH) and calibrationless
motion-resolved model-based reconstruction. Methods: Free-running
(free-breathing, retrospective cardiac gating) IR radial FLASH is used for data
acquisition at 3T. First, to reduce the waiting time between inversions, an
analytical formula is derived that takes the incomplete T1 recovery into
account for an accurate T1 calculation. Second, the respiratory motion signal
is estimated from the k-space center of the contrast varying acquisition using
an adapted singular spectrum analysis (SSA-FARY) technique. Third, a
motion-resolved model-based reconstruction is used to estimate both parameter
and coil sensitivity maps directly from the sorted k-space data. Thus,
spatio-temporal total variation, in addition to the spatial sparsity
constraints, can be directly applied to the parameter maps. Validations are
performed on an experimental phantom, eleven human subjects, and a young
landrace pig with myocardial infarction. Results: In comparison to an IR
spin-echo reference, phantom results confirm good T1 accuracy, when reducing
the waiting time from five seconds to one second using the new correction. The
motion-resolved model-based reconstruction further improves T1 precision
compared to the spatial regularization-only reconstruction. Aside from showing
that a reliable respiratory motion signal can be estimated using modified
SSA-FARY, in vivo studies demonstrate that dynamic myocardial T1 maps can be
obtained within two minutes with good precision and repeatability. Conclusion:
Motion-resolved myocardial T1 mapping during free-breathing with good accuracy,
precision and repeatability can be achieved by combining inversion-recovery
radial FLASH, self-gating and a calibrationless motion-resolved model-based
reconstruction.Comment: Part of this work has been presented at the ISMRM Annual Conference
2021 (Virtual), submitted to Magnetic Resonance in Medicin
Equicontinuous factors, proximality and Ellis semigroup for Delone sets
We discuss the application of various concepts from the theory of topological
dynamical systems to Delone sets and tilings. We consider in particular, the
maximal equicontinuous factor of a Delone dynamical system, the proximality
relation and the enveloping semigroup of such systems.Comment: 65 page
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