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- Bergvall, Erik, et al.
(författare)
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A fast and highly automated approach to myocardial motion analysis using phase contrast magnetic resonance imaging.
- 2006
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Ingår i: Journal of Magnetic Resonance Imaging. - : Wiley. - 1522-2586 .- 1053-1807. ; 23:5, s. 652-661
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To develop a fast and highly automated method for calculating two-dimensional myocardial motion and deformation using velocity encoded magnetic resonance imaging. Materials and Methods: Two-dimensional phase contrast magnetic resonance imaging was used to acquire time resolved velocity maps of the myocardium. Cardiac motion was calculated by an iterative integration-regularization scheme of low computational cost. Image segmentation was performed using active appearance models. Results: Validation of motion tracking was performed in N = 47 subjects using saturation grid-tagging and closely followed "tag-lines." Image segmentation was validated vs. manual delineation. Conclusion: The speed and limited user interaction gives the method good potential for use in clinical practice.
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- Bergvall, Erik, et al.
(författare)
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Regularization of phase contrast magnetic resonance images using optical flow and smoothness constraints
- 2005
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Ingår i: Computers in Cardiology. - 0276-6574. ; 32, s. 33-36
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Konferensbidrag (refereegranskat)abstract
- This paper presents a post processing strategy for myocardial velocity fields obtained by phase contrast magnetic resonance imaging. Such data can be used to track cardiac motion and to calculate strain. The method combines data regularization with optical flow estimation to overcome the partial volume effect in the image acquisition. Validation is performed both in vitro and in vivo and it is shown that the method improves the accuracy of cardiac motion tracking.
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- Bergvall, Erik, et al.
(författare)
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Spline-based cardiac motion tracking using velocity-encoded magnetic resonance imaging.
- 2008
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Ingår i: IEEE Transactions on Medical Imaging. - 1558-254X. ; 27:8, s. 1045-1053
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Tidskriftsartikel (refereegranskat)abstract
- This paper deals with the problem of tracking cardiac motion and deformation using velocity-encoded magnetic resonance imaging. We expand upon an earlier described method and fit a spatiotemporal motion model to measured velocity data. We investigate several different spatial elements both qualitatively and quantitatively using phantom measurements and data from human subjects. In addition, we also use optical flow estimation by the Horn-Schunk method as complementary data in regions where the velocity measurements are noisy. Our results show that it is possible to obtain good motion tracking accuracy in phantoms with relatively few spatial elements, if the type of element is properly chosen. The use of optical flow can correct some measurement artifacts but may give an underestimation of the magnitude of the deformation. In human subjects the different spatial elements perform quantitatively in a similar way but qualitative differences exists, as shown by a semiquantitative visual scoring of the different methods.
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- Berthilsson, Rikard, et al.
(författare)
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Recursive Structure and Motion from Image Sequences using Shape and Depth Spaces
- 1997
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Ingår i: [Host publication title missing]. - 1063-6919. ; , s. 444-449
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this paper a novel recursive method for estimating structure and motion from image sequences is presented. The novelty lies in the fact that the output of the algorithm is independent of the chosen coordinate systems in the images as well as the ordering of the points. It relies on subspace methods and is derived from both ordinary coordinate representations and camera matrices and from a so called depth and shape analysis. Furthermore, no initial phase is needed to start up the algorithm. It starts directly with the first two images and incorporates new images as soon as new corresponding points are obtained. The performance of the algorithm is shown on simulated data. Moreover, the two different approaches, one using camera matrices and the other using the concepts of affine shape and depth, are unified into a general theory of structure and motion from image sequences.
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- Cwikel, Michael, et al.
(författare)
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Jaak Peetre, the man and his work
- 2002
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Ingår i: Function spaces, interpolation theory and related topics. - Berlin : Walter de Gruyter. - 3110171171 ; , s. 1-22
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Konferensbidrag (refereegranskat)
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- Diehl, Stefan, et al.
(författare)
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Analytical and numerical description of the settling process in the activated sludge operation
- 1990
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Ingår i: Instrumentation, control, and automation of water and wastewater treatment and transport systems : proceedings of the 5th IAWPRC Workshop held in Yokohama and Kyoto, Japan, 26 July-3 August 1990. - 0080407765 ; , s. 471-478
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Konferensbidrag (refereegranskat)abstract
- The secondary clarifier or settler is crucial for the whole activated sludge operation. Consequently, it is important to obtain a reliable analytical model as well as a useful numerical method, which can be used in the automatic control of the settling process. Discontinuities (shocks) appear physically, and an analytical description as well as a stable numerical algorithm must be able to handle these discontinuities. A model based on the Kynch theory of sedimentation is used, where the settling flux is a function only of the local concentration and is assumed to have one inflexion point. For such non-convex flux functions, the settling process is qualitatively the same, independent of further assumptions on the shapes of the settling functions. Using the theory of nonlinear conservation laws, the main results obtained are: how to calculate transient and asymptotic behavior; how to control the concentration profile of the settler, in particular the depth of the sludge blanket, for a given load; and, a numerical algorithm which automatically preserves shocks and gives the physically correct solution according to the analytical treatment. The algorithm can be applied on any flux function (with more than one inflexion point).
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