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- Eriksson, Ola, 1967-, et al.
(author)
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In vitro evaluation of brain lesioning electrodes (Leksell) using a computer-assisted video system
- 1999
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In: Neurological Research. - 0161-6412 .- 1743-1328. ; 21:1, s. 89-95
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Journal article (peer-reviewed)abstract
- Radiofrequency (RF) generated thermal brain lesions are widely used in functional neurosurgery. The size, shape and development of the lesions depends on system parameter settings and the electrode configuration. Difficulties in studying the effect of these factors in vivo stimulated us to develop an in vitro system for standardized comparison between different electrodes and physical parameters. A computer-assisted video system was set-up allowing continuous video recording of RF-generated coagulations in either a standard albumin solution or in the fresh white of a hen's egg as transparent test substrates. Ten lesions were made with each test electrode (two bipolar and three monopolar) in each of the two substrates at 70 degrees, 80 degrees and 90 degrees C (t = 60 sec). Due to the better homogeneity the lesions in the albumin solution were much more regular and reproducible. This made it possible to calculate the size (width 2.2 +/- 0.1 to 5.3 +/- 0.1 mm and length 3.0 +/- 0.1 to 8.7 +/- 0.3 mm) as well as the volume (8.5 +/- 1.4 mm3 to 133.5 +/- 26.8 mm3). It is concluded that this in vitro system offers a reproducible way to study and document the effect of different electrode configurations and RF-generator settings on the formation of a heat lesion. Even if the results are not directly applicable to the living human brain they give an estimate of the form and size of a coagulation lesion and can be of value for standardized comparisons between different electrodes.
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| 2. |
- Eriksson Bylund, Nina, et al.
(author)
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3D Wiener filtering to reduce reverberations in ultrasound image sequences
- 2003
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In: Image Analysis. - : Springer. - 3540406018 - 9783540406013 ; , s. 579-586
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Book chapter (peer-reviewed)abstract
- One of the most frequently occuring artifacts in ultrasound imaging is reverberations. These are multiple reflection echoes that result in ghost echoes in the ultrasound image. A method for reducing these unwanted artifacts using a three-dimensional (3D) Wiener filter is presented. The Wiener filter is a global filter and produces an estimate of the uncorrupted signal by minimizing the mean square error between the estimate and the uncorrupted signal in a statistical sense. The procedure works as follows: In a graphic interface the operator is displayed an image sequence. The operator marks two areas in one of the images, one area which contains a typical reverberation artifact, and one area free from artifact. Using these areas to produce noise and signal estimates, a Wiener filter is created and applied to the sequence. The 3D Wiener filters display excellent selection capabilities, and the developed method significantly reduces the magnitude of the reverberation artifact in the tested sequences.
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| 4. |
- Eriksson-Bylund, Nina, 1971-, et al.
(author)
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Interactive 3D filter design for ultrasound artifact reduction
- 2005
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In: Image Processing, 2005. ICIP 2005. IEEE International Conference on (Volume:3 ). - 0780391349 ; , s. 728-731
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Conference paper (peer-reviewed)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.
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| 5. |
- Eriksson-Bylund, Nina, et al.
(author)
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Reverberation Reduction Using 3D Wiener Filtering
- 2003
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Conference paper (other academic/artistic)abstract
- One of the most common artifacts in ultrasound imaging is reverberations. These are multiple reflection echoes that register as coming from a deeper region than the depth of the interface that are causing them, and result in ghost echoes in the ultrasound image. A method to reduce these unwanted artifacts using a three dimensional (2D + time) Wiener filter has been developed. Two sequences of iq-data, the least processed signal possible to retrieve from the ultrasound system (Vingmed System Five), have been used to test the method: One sequence on a tissue-mimicking agar gel phantom in which bars of glass simulating ribs give rise to reverberations, and one sequence on an open-chest pig with a strong reverberation from a water-filled rubber glove used as a medium between the heart and the transducer. The procedure works as follows: In a graphic interface the operator is shown the image sequence. In one of the frames two areas must be marked out; One area which contains a typical reverberation artifact, and one area which will represent an artifact free signal. After creating the three dimensional Wiener filter post-processing of the sequence is performed. The developed method significantly reduced the magnitude of the reverberation artifact in the tested sequences.
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| 6. |
- Eriksson-Bylund, Nina, 1971-
(author)
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Spatio-temporal filtering of ultrasound image sequences
- 2004
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Licentiate thesis (other academic/artistic)abstract
- A number of diseases result in reduced perfusion of the vital organs of the body. Measures of the blood flow in the small vessels (the perfusion) of these organs would contribute significantly to a clinical diagnosis. Myocardial contrast echocardiography is a rapidly developing technique for non-invasive ultrasound imaging of perfusion. The work presented in this thesis is related to the preprocessing of the ultrasound data in order to facilitate the segmentation of the heart walls in which the perfusion is to be estimated.In an ultrasound image artifacts can occur for a number of reasons. These lead to a more complicated interpretation procedure as important information may be obscured or lost. One of the most frequently occuring artifacts in diagnostic ultrasound imaging is reverberation. This type of artifact is caused by the incorrect assumption that the ultrasound pulse's propagation path is always straight to a backscattering target and straight back to the transducer. Reverberation artifacts may be seen as multiple ghost structures in the ultrasound image.A method to detect these reverberation artifacts has been developed and tested on three different ultrasound image sequences. The method uses ratios of lognormal quadrature filter responses to estimate the local bandwidth of the ultrasound signal. For the in-vivo sequences the result is a "map" indicating the artifact locations.In order to reduce the reverberation artifacts an interactive procedure for estimating two dimensional and three-dimensional Wiener filters has been developed. The design procedure used is a weighted least squares approach, in which both a frequency and a spatiotemporal weighting function are used to optimize the filter. In the results after filtering with the optimized filters the magnitude of the artifact is significantly reduced. For the in-vivo sequences the 3D approach display a better selection capability compared to the 2D approach.The results from these studies show that the proposed methods constitute a promising basis for a useful clinical tool.
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