| 1. |
- Andersson, Kenneth, 1970-, et al.
(författare)
-
Prediction from off-grid samples using continuous normalized convolution
- 2007
-
Ingår i: Signal Processing. - : Elsevier BV. - 0165-1684 .- 1872-7557. ; 87:3, s. 353-365
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a novel method for performing fast estimation of data samples on a desired output grid from samples on an irregularly sampled grid. The output signal is estimated using integration of signals over a neighbourhood employing a local model of the signal using discrete filters. The strength of the method is demonstrated in motion compensation examples by comparing to traditional techniques.
|
|
| 2. |
- Brun, Anders, 1976-, et al.
(författare)
-
A tensor-like representation for averaging, filtering and interpolation of 3D object orientation data
- 2005
-
Ingår i: Image Processing, 2005. ICIP 2005. IEEE International Conference on (Volume:3 ). - 0780391349 ; , s. 1092-1095
-
Konferensbidrag (refereegranskat)abstract
- Averaging, filtering and interpolation of 3-D object orientation data is important in both computer vision and computer graphics, for instance to smooth estimates of object orientation and interpolate between keyframes in computer animation. In this paper we present a novel framework in which the non-linear nature of these problems is avoided by embedding the manifold of 3-D orientations into a 16-dimensional Euclidean space. Linear operations performed in the new representation can be shown to be rotation invariant, and defining a projection back to the orientation manifold results in optimal estimates with respect to the Euclidean metric. In other words, standard linear filters, interpolators and estimators may be applied to orientation data, without the need for an additional machinery to handle the non-linear nature of the problems. This novel representation also provides a way to express uncertainty in 3-D orientation, analogous to the well known tensor representation for lines and hyperplanes.
|
|
| 3. |
- Brun, Anders, 1976-, et al.
(författare)
-
Fast manifold learning based on Riemannian normal coordinates
- 2005
-
Ingår i: Image Analysis. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783540263203 - 9783540315667 ; , s. 920-
-
Konferensbidrag (refereegranskat)abstract
- We present a novel method for manifold learning, i.e. identification of the low-dimensional manifold-like structure present in a set of data points in a possibly high-dimensional space. The main idea is derived from the concept of Riemannian normal coordinates. This coordinate system is in a way a generalization of Cartesian coordinates in Euclidean space. We translate this idea to a cloud of data points in order to perform dimension reduction. Our implementation currently uses Dijkstra’s algorithm for shortest paths in graphs and some basic concepts from differential geometry. We expect this approach to open up new possibilities for analysis of e.g. shape in medical imaging and signal processing of manifold-valued signals, where the coordinate system is “learned” from experimental high-dimensional data rather than defined analytically using e.g. models based on Lie-groups.
|
|
| 4. |
|
|
| 5. |
- Brun, Anders, 1976-, et al.
(författare)
-
Intrinsic and Extrinsic Means on the Circle -- a Maximum Likelihood Interpretation
- 2007
-
Ingår i: ICASSP 2007. IEEE International Conference on Acoustics, Speech and Signal Processing, 2007. - New York, USA : IEEE. - 1424407273 ; , s. III-1053-III-1056
-
Konferensbidrag (refereegranskat)abstract
- For data samples in Rn, the mean is a well known estimator. When the data set belongs to an embedded manifold M in Rn, e.g. the unit circle in R2, the definition of a mean can be extended and constrained to M by choosing either the intrinsic Riemannian metric of the manifold or the extrinsic metric of the embedding space. A common view has been that extrinsic means are approximate solutions to the intrinsic mean problem. This paper study both means on the unit circle and reveal how they are related to the ML estimate of independent samples generated from a Brownian distribution. The conclusion is that on the circle, intrinsic and extrinsic means are maximum likelihood estimators in the limits of high SNR and low SNR respectively
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
- Brun, Anders, 1976-, et al.
(författare)
-
Using Importance Sampling for Bayesian Feature Space Filtering
- 2007
-
Ingår i: Proceedings of the 15th Scandinavian conference on image analysis. - Berlin, Heidelberg : Springer-Verlag. - 9783540730392 ; , s. 818-827
-
Konferensbidrag (refereegranskat)abstract
- We present a one-pass framework for filtering vector-valued images and unordered sets of data points in an N-dimensional feature space. It is based on a local Bayesian framework, previously developed for scalar images, where estimates are computed using expectation values and histograms. In this paper we extended this framework to handle N-dimensional data. To avoid the curse of dimensionality, it uses importance sampling instead of histograms to represent probability density functions. In this novel computational framework we are able to efficiently filter both vector-valued images and data, similar to e.g. the well-known bilateral, median and mean shift filters.
|
|
| 9. |
- Eriksson-Bylund, Nina, 1971-, et al.
(författare)
-
Interactive 3D filter design for ultrasound artifact reduction
- 2005
-
Ingår i: Image Processing, 2005. ICIP 2005. IEEE International Conference on (Volume:3 ). - 0780391349 ; , s. 728-731
-
Konferensbidrag (refereegranskat)abstract
- A method for detecting and reducing reverberation artifacts in ultrasound image sequences is described. A reverberation artifact localization map is produced using local Rf-bandwidth estimation. To reduce the artifacts an ideal 3D (2D + time) Wiener filter function is computed by using the reverberation map to interactively produce an estimate of the noise and signal spectra. The Wiener filter kernel is optimized to obtain good locality properties. The optimized filter is then applied to the ultrasound image sequence. The test sequence used is from an open chest pig heart, corrupted by strong reverberation artifacts. The selective power of a 3D filter is far superior to that of ID and 2D filters and the reverberation artifacts are almost completely removed by the developed method.
|
|
| 10. |
- Herberthson, Magnus, 1963-, et al.
(författare)
-
Pairs of orientation in the plane
- 2006
-
Ingår i: SSBA Symposium on Image Analysis,2006. ; , s. 97-100
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)
|
|
| 11. |
- Herberthson, Magnus, 1963-, et al.
(författare)
-
Representing Pairs of Orientations in the Plane
- 2007
-
Ingår i: Image Analysis. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783540730392 - 9783540730408 ; , s. 661-670
-
Konferensbidrag (refereegranskat)abstract
- In this article we present a way of representing pairs of orientations in the plane. This is an extension of the familiar way of representing single orientations in the plane. Using this framework, pairs of lines can be added, scaled and averaged over in a sense which is to be described. In particular, single lines can be incorporated and handled simultaneously.
|
|
| 12. |
- Knutsson, Hans, 1950-, et al.
(författare)
-
Morphones : Paint on priors and elastic canvas for segmentation and registration
- 2005
-
Ingår i: Image Analysis. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783540263203 - 9783540315667 ; , s. 292-301
-
Konferensbidrag (refereegranskat)abstract
- This paper presents a new robust approach for registration and segmentation. Segmentation as well as registration is attained by morphing of an N-dimensional model, the Morphon, onto the Ndimensional data. The approach is general and can, in fact, be said to encompass much of the deformable model ideas that have evolved over the years. However, in contrast to commonly used models, a distinguishing feature of the Morphon approach is that it allows an intuitive interface for specifying prior information, hence the expression paint on priors. In this way it is simple to design Morphons for specific situations.The priors determine the behavior of the Morphon and can be seen as local data interpreters and response generators. There are three different kinds of priors: – material parameter fields (elasticity, viscosity, anisotropy etc.), – context fields (brightness, hue, scale, phase, anisotropy, certainty etc.) and – global programs (filter banks, estimation procedures, adaptive mechanisms etc.).The morphing is performed using a dense displacement field. The field is updated iteratively until a stop criterion is met. Both the material parameter and context fields are addressed via the present displacement field. In each iteration the neighborhood operators are applied, using both data and the displaced parameter fields, and an incremental displacement field is computed.An example of the performance is given using a 2D ultrasound heart image sequence where the purpose is to segment the heart wall. This is a difficult task even for trained specialists yet the Morphon generated segmentation is highly robust. Further it is demonstrated how the Morphon approach can be used to register the individual images. This is accomplished by first finding the displacement field that aligns the morphon model with the heart wall structure in each image separately and then using the displacement field differences to align the images.
|
|
| 13. |
- Knutsson, Hans, 1950-, et al.
(författare)
-
Morphons : Segmentation using elastic canvas and paint on priors
- 2005
-
Ingår i: Image Processing, 2005. ICIP 2005. IEEE International Conference on (Volume:2 ). - 0780391349 ; , s. 1226-1229
-
Konferensbidrag (refereegranskat)abstract
- This paper presents a new robust approach for segmentation. The segmentation is attained by morphing of an TV-dimensional model, the Morphon, onto the TV-dimensional data. The approach is general and can, in fact, be said to encompass much of the deformable model ideas that have evolved over the years. However, in contrast to commonly used models, a distinguishing feature of the Morphon approach is that it allows an intuitive interface for specifying prior information, hence the expression paint on priors. In this way it is simple to design Morphons for specific situations. The priors determine the behavior of the Morphon and can be seen as local data interpreters and response generators. There are three different kinds of priors: material parameter fields (elasticity, viscosity, anisotropy etc.), context fields (brightness, hue, scale, phase, anisotropy, certainly etc.) and global programs (filter banks, estimation procedures, adaptive mechanisms etc.). The morphing is performed using a dense displacement field. Both the material parameter and context fields are addressed via the present displacement field. An example of the performance of is given using 2D ultrasound images of a heart where the purpose is to segment the heart wall.
|
|
| 14. |
|
|
| 15. |
- Langer, Max, 1978-, et al.
(författare)
-
Design of fast multidimensional filters using genetic algorithms
- 2005
-
Ingår i: Applications of Evolutionary Computing. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783540253969 - 9783540320036 ; , s. 366-375
-
Konferensbidrag (refereegranskat)abstract
- A method for designing fast multidimensional filters using genetic algorithms is described. The filter is decomposed into component filters where coefficients can be sparsely scattered using filter networks. Placement of coefficients in the filters is done by genetic algorithms and the resulting filters are optimized using an alternating least squares approach. The method is tested on a 2-D quadrature filter and the method yields a higher quality filter in terms of weighted distortion compared to other efficient implementations that require the same ammount of computations to apply. The resulting filter also yields lower weighted distortion than the full implementation.
|
|
| 16. |
- Ohlsson, Henrik, 1981-, et al.
(författare)
-
Direct Weight Optimization Applied to Discontinuous Functions
- 2008
-
Ingår i: 47th IEEE Conference on Decision and Control, 2008. CDC 2008. - Cancun, Mexico : IEEE. - 9781424431236 ; , s. 117-122
-
Konferensbidrag (refereegranskat)abstract
- The Direct Weight Optimization (DWO) approach is a nonparametric estimation approach that has appeared in recent years within the field of nonlinear system identification. In previous work, all function classes for which DWO has been studied have included only continuous functions. However, in many applications it would be desirable also to be able to handle discontinuous functions. Inspired by the bilateral filter method from image processing, such an extension of the DWO framework is proposed for the smoothing problem. Examples show that the properties of the new approach regarding the handling of discontinuities are similar to the bilateral filter, while at the same time DWO offers a greater flexibility with respect to different function classes handled.
|
|
| 17. |
- Ohlsson, Henrik, 1981-, et al.
(författare)
-
Enabling Bio-Feedback using Real-Time fMRI
- 2008
-
Ingår i: 47th IEEE Conference on Decision and Control, 2008, CDC 2008. - Linköping : IEEE. - 9781424431236 ; , s. 3336-3341
-
Konferensbidrag (refereegranskat)abstract
- Despite the enormous complexity of the human mind, fMRI techniques are able to partially observe the state of a brain in action. In this paper we describe an experimental setup for real-time fMRI in a bio-feedback loop. One of the main challenges in the project is to reach a detection speed, accuracy and spatial resolution necessary to attain sufficient bandwidth of communication to close the bio-feedback loop. To this end we have banked on our previous work on real-time filtering for fMRI and system identification, which has been tailored for use in the experiment setup. In the experiments presented the system is trained to estimate where a person in the MRI scanner is looking from signals derived from the visual cortex only. We have been able to demonstrate that the user can induce an action and perform simple tasks with her mind sensed using real-time fMRI. The technique may have several clinical applications, for instance to allow paralyzed and "locked in" people to communicate with the outside world. In the meanwhile, the need for improved fMRI performance and brain state detection poses a challenge to the signal processing community. We also expect that the setup will serve as an invaluable tool for neuro science research in general.
|
|
| 18. |
- Pettersson, Johanna, 1977-, et al.
(författare)
-
A hip surgery simulator based on patient specific models generated by automatic segmentation
- 2006
-
Ingår i: Medicine Meets Virtual Reality 14: Accelerating Change in Healthcare. - Amsterdam, Nederländerna : IOS Press. - 9781586035839 ; , s. 431-436
-
Konferensbidrag (refereegranskat)abstract
- The use of surgical simulator systems for education and preoperative planning is likely to increase in the future. A natural course of development of these systems is to incorporate patient specific anatomical models. This step requires some kind of segmentation process in which the different anatomical parts are extracted. Anatomical datasets are, however, usually very large and manual processing would be too demanding. Hence, automatic, or semi-automatic, methods to handle this step are required. The framework presented in this paper uses nonrigid registration, based on the morphon method, to automatically segment the hip anatomy and generate models for a hip surgery simulator system.
|
|
| 19. |
- Pettersson, Johanna, 1977-, et al.
(författare)
-
Automatic hip bone segmentation using non-rigid registration
- 2006
-
Ingår i: 18th International Conference on Pattern Recognition, 2006, ICPR 2006 (Volume:3 ). - : IEEE Computer Society. - 0769525210 ; , s. 946-949
-
Konferensbidrag (refereegranskat)abstract
- This paper presents a method for automatic segmentation of bone from volumetric computed tomography (CT) data. Due to osteoporosis, which degenerates the bone density and hence decreases the intensity of the bone in the CT dataset, it is not possible to use conventional thresholding techniques to handle the segmentation. Furthermore we want to use prior knowledge about shapes and relations of the bones in the area of interest to be able to e.g. separate adjoining bones from each other. The method we suggest is the morphon algorithm in Knutsson and Andersson (2005). This is a non-rigid registration technique where an 2D or 3D image is iteratively deformed to match the corresponding structure in a target image. The method uses difference in local quadrature phase and certainty measures to estimate the deformations
|
|
| 20. |
- Pettersson, Johanna, 1977-, et al.
(författare)
-
Generation of patient specific bone models from volume data using morphons
- 2005
-
Ingår i: IFMBE Proceedings. - Umeå : IFMBE. ; , s. 199-200
-
Konferensbidrag (refereegranskat)abstract
- The use of simulator systems for surgical planning and training is growing as the systems become more advanced. One important feature of these systems is the possibility to work on real patient data. This paper presents a method for generating patient-specific models of the femoral bone and the pelvis to be used in a hip surgery simulator. The bones are segmented from volumetric CT data using the Morphon method [3], where a prototype pattern is iteratively morphed to fit the corresponding structure in the input data.
|
|
| 21. |
- Pettersson, Johanna, 1977-, et al.
(författare)
-
Non-rigid registration for automatic fracture segmentation
- 2006
-
Ingår i: Image Processing, 2006. - Atlanta : IEEE. - 1424404800 ; , s. 1185-1188
-
Konferensbidrag (refereegranskat)abstract
- Automatic segmentation of anatomical structures is often performed using model-based non-rigid registration methods. These algorithms work well when the images do not contain any large deviations from the normal anatomy. We have previously used such a method to generate patient specific models of hip bones for surgery simulation. The method that was used, the morphon method, registers two-or three-dimensional images using a multi-resolution deformation scheme. A prototype image is iteratively registered to a target image using quadrature filter phase difference to estimate the local displacement. The morphon method has in this work been extended to deal with automatic segmentation of fractured bones. Two features have been added. First, the method is modified such that multiple prototypes (in this case two) can be used. Second, normalised convolution is utilized for the displacement estimation, to guide the registration of the second prototype, based on the result of the registration of the first one
|
|
| 22. |
|
|
| 23. |
- Pettersson, Johanna, 1977-, et al.
(författare)
-
Segmentation and registration with the Morphon method, four different applications
- 2007
-
Ingår i: Proceedings of the {SSBA} Symposium on Image Analysis,2007.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Morphon method has shown to be a useful non-rigid registration method since it was first presented in 2005. This paper demonstrates how the method has been adapted for four different applications; hip fracture segmentation from CT data, hippocampus segmentation from MR data and registration the prostate and the head-neck region from CT data for radiotherapy planning.
|
|
| 24. |
|
|
| 25. |
- Rodríguez-Vila, Borja, et al.
(författare)
-
3D deformable registration for monitoring radiotherapy treatment in prostate cancer
- 2007
-
Ingår i: Image Analysis. - Berlin/Heidelberg, Germany : Springer Berlin/Heidelberg. - 9783540730392 - 3540730400 - 9783540730408 ; , s. 750-759
-
Konferensbidrag (refereegranskat)abstract
- Two deformable registration methods, the Demons and the Morphon algorithms, have been used for registration of CT datasets to evaluate their usability in radiotherapy planning for prostate cancer. These methods were chosen because they can perform deformable registration in a fully automated way. The experiments show that for intrapatient registration both of the methods give useful results, although some differences exist in the way they deform the template. The Morphon method has, however, some advantageous compared to the Demons method. It is invariant to the image intensity and it does not distort the deformed data. The conclusion is therefore to recommend the Morphon method as a registration tool for this application. A more flexible regularization model is needed, though, in order to be able to catch the full range of deformations required to match the datasets.
|
|
