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- Hemmendorff, Magnus, 1972-
(författare)
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Motion estimation and compensation in medical imaging
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This dissertation presents a framework for estimation of motion fields in 2D images, 3D volumes and multi-dimensional signal registration. The primary application is motion compensation for sequences of medical images and volumes with contrast agents.The framework implies motion estimation in two steps where the intermediate result is constraints on the local motion vectors. One algorithm generates constraints and a second algorithm computes motion vector fields.We present two methods for generation of local motion constraints. The first method is based on phase from quadrature filters. The second method is based on canonical correlation and scalar products of quadrature filters. In both methods, a local confidence measure produced to increase accuracy and robustness.A mathematical result is a novel method for maximizing canonical correlation. The novel method can handle covariance matrices that are complex and singular.Parametric models, such as affine or finite elements, are used to estimate motion fields from local motion constraints and confidence measures. In order to control smoothness, the model is extended to incorporate stiffness and cost of deformations.Multiple layers of motion fields are estimated using implicit or explicit clustering of motion constraints. We also discuss some philosophical issues in the analysis of multiple motions. An extension of the known EM algorithm is presented together with experimental results on multiple layers for 2D images and 3D volumes. As an alternative to the EM algorithm, this thesis also introduces a method based on higher order outer products. In addition, we present a back projection algorithm for reconstruction of transparent layers.Clinical evaluation shows good results for 2D X-ray angiography images. Experimental results also show accurate motion estimates for 3D MRI mammograms and simulated images in 3D angiography.
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- Hemmendorff, Magnus, 1972-
(författare)
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Single and Multiple Motion Field Estimation
- 1999
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents a framework for estimation of motion fields both for single and multiple layers. All the methods have in common that they generate or use constraints on the local motion. Motion constraints are represented by vectors whose directions describe one component of the local motion and whose magnitude indicate confidence.Two novel methods for estimating these motion constraints are presented. Both methods take two images as input and apply orientation sensitive quadrature filters. One method is similar to a gradient method applied on the phase from the complex filter outputs. The other method is based on novel results using canonical correlation presented in this thesis.Parametric models, e.g. affine or FEM, are used to estimate motion from constraints on local motion. In order to estimate smooth fields for models with many parameters, cost functions on deformations are introduced.Motions of transparent multiple layers are estimated by implicit or explicit clustering of motion constraints into groups. General issues and difficulties in analysis of multiple motions are described. An extension of the known EM algorithm is presented together with experimental results on multiple transparent layers with affine motions. Good accuracy in estimation allows reconstruction of layers using a backprojection algorithm. As an alternative to the EM algorithm, this thesis also introduces a method based on higher order tensors.A result with potential applicatications in a number of diffeerent research fields is the extension of canonical correlation to handle complex variables. Correlation is maximized using a novel method that can handle singular covariance matrices.
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