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- Jansson, Tomas, et al.
(författare)
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Ultrasound Doppler Vector Tomography - Measurements of Directional Blood Flow
- 1997
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Ingår i: Ultrasound in Medicine and Biology. - 0301-5629. ; 23:1, s. 47-57
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Tidskriftsartikel (refereegranskat)abstract
- An experimental system has been developed to verify the possibility of detecting flow activity using a technique called ultrasound Doppler vector tomography. A tomography algorithm is used to reconstruct blood flow vector fields using data from computer-controlled ultrasound continuous-wave Doppler scanning equipment. The result is a picture in which the brightness variations represent the reconstructed values of the curl of the velocity field (del x v). Continuous ultrasound is transmitted into a region with flow activity and the Doppler-shifted signals are received. To obtain measurement data suited for fan beam tomography, the scanning is performed in a plane from points encircling the region. Reconstructions have been achieved using measurement data from two different flow phantoms. A comparison between the experimental results and simulations shows good conformity. Copyright (C) 1997 World Federation for Ultrasound in Medicine & Biology.
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| 2. |
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| 3. |
- Karlsson, Adam, et al.
(författare)
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Segmentation of Histopathological Sections Using Snakes
- 2003
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Ingår i: Image Analysis. - : Springer. - 9783540406013 - 9783540451037 ; 2749, s. 595-602
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Konferensbidrag (refereegranskat)abstract
- This paper presents a semi-automatic method for segmentation of digital images. The segmentation method is based on snakes and a novel implementation of the snake evolution algorithm is presented. Analytical expressions describing the snake evolution are derived using the Fourier transform. These expressions can be sampled and used in a fast algorithm for snake propagation. Experiments are carried out on images of histopathological tissue sections and the results are very promising. In particular the method is able to cope with overlapping nuclei.
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| 6. |
- Stråhlén, Kent, et al.
(författare)
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Exponential Vector Field Tomography
- 1997
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Ingår i: Lecture Note in Computer Science. V. 1311. - 3 540 63508 4 ; 2, s. 348-355
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In the exponential Radon transform in R2, the integrals of a scalar function f over lines, with exponential weight functions, are determined. We demonstrate how to define two different kinds of exponential Radon transforms for vector fields in R2 in a natural way. It is shown that having data from these transforms it is possible to reconstruct the vector field uniquely. The motivation for the study of this problem is ultrasound measurements of flows, from which velocity spectra along lines can be determined. The first moment of these can be interpreted by means of one of the exponential vectorial Radon transforms
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| 9. |
- Stråhlén, Kent
(författare)
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Studies of vector tomography
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The motivation to study the kind of problems appearing in this thesis has been ultrasound measurements of flows, from which velocity spectra along lines can be determined. These velocity spectra can mathematically be described by a new non-linear transform, here called the Doppler Spectral Transform (DST). The Doppler spectral transform has a very rich theory, into which some steps are taken here. Although the problems of existence and uniqueness of an inverse of the Doppler spectral transform remain unsolved, partial results are obtained. For a discrete counterpart, based on a log-polar decomposition, full understanding is achieved. The first moment of the Doppler spectral transform can be interpreted by means of a vectorial X-ray transform, where integration is made over the components of the vector field along the ray of integration. Using other components, other vectorial integral transforms are obtained, in particular the normal flow Radon transform. In the two dimensional case these transforms are extended to exponential transform of vector fields. Also the possibility of local tomography of vector fields by means of wavelets is discussed. Some steps towards a general vectorial k-plane transform for vector fields are taken. The problem of reconstructing the flow from the vectorial X-ray transform and normal flow Radon transform is solved, in the non-exponential case in any dimension and in the exponential case in two dimensions. Some results are presented on how to generalise the reconstruction process to the more general setting of sets of vectorial k-plane transforms. Finally a numerical method to regain the full flow from the Doppler spectral transform is presented. In a preprocessing step, the first moment of the Doppler spectral transform is used to generate a start solution for iteration, and the zeroth moment to determine the region of reflecting particles.}
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