Background We demonstrate that projection imaging significantly reduces the prevalence and spatial extent of subendocardial dark-rim artifacts (DRAs) in first-pass perfusion (FPP) myocardial MR, compared to conventional Cartesian techniques. A major cause of DRAs, which remain a major concern in FPP imaging, is known to be the socalled Gibbs ringing (truncation) phenomenon [1-3]. Radial k-space...

We consider truncated SVD (or spectral cut-off, projection) estimators for a prototypical statistical inverse problem in dimension D. Since calculating the singular value decomposition (SVD) only for the largest singular values is much less costly than the full SVD, our aim is to select a data-driven truncation level m̂ ∈ {1, . . . , D} only based on the knowledge of the first m̂ singular values ...

The main focus of this paper is on an a-posteriori analysis for different model-order strategies applied to optimal control problems governed by linear parabolic partial differential equations. Based on a perturbation method it is deduced how far the suboptimal control, computed on the basis of the reduced-order model, is from the (unknown) exact one. For the model-order reduction, H2,α-norm op...

We introduce a general procedure for obtaining a low-dimensional linear time-periodic model from a very high-dimensional nonlinear system that has an asymptotically stable periodic orbit. Our goal is to develop models that are suitable for designing feedback controllers for fluids systems with periodic orbits, such as periodically shedding wakes, or flow control problems where periodic actuatio...

Laboratory observations and numerical experiments have shown that a variety of compound vortices can emerge in two-dimensional flow due to the instability of isolated circular vortices. The simple geometrical features of these compound vortices suggest that their description may take a simple form if an appropriately chosen set of functions is used. We employ a set which is complete on the infi...

This article gives an overview of essential requirements and limitations in the quantitative assessment of regional myocardial perfusion or regional myocardial blood flow (rMBF) using existing clinical SPECT systems in clinical settings. One major requirement is the need for acquiring complete projection data without truncation. Attenuation and scatter are then prerequisites to reproduce quanti...

Ideal integrating nephelometers integrate light scattered by particles over all directions. However, real nephelometers truncate light scattered in near-forward and near-backward directions below a certain truncation angle ~typically 7°!. This results in truncation errors, with the forward truncation error becoming important for large particles. Truncation errors are commonly calculated using M...

In single photon emission computed tomography (SPECT), a varying-focal-length cone-beam collimator can be used to reduce the truncation problem and to maintain sensitivity when imaging the organ of interest. The collimator is constructed so that the collimator holes focus to a circular symmetric, spatially varying, focal point function. The focal length increases radially from the shortest foca...

In order to detect a buried object quickly and accurately, a fast radar imaging method is presented in this paper. At first, complex backscatter data are computed by using propagation-insidelayer expansion combining the forward and backward method (PILE + FB). Then, a conventional synthetic aperture radar (SAR) imaging procedure called back projection method is used to generate 2-D image. The r...

In this paper we are interested in the studying coarse-graining in field theories using the language of quantum open systems. Motivated by the ideas of Calzetta and Hu [1] on correlation histories we employ the Zwanzig projection technique to obtain evolution equations for relevant observables in self-interacting scalar field theories. Our coarsegraining operation consists in concentrating sole...