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- Brandt Heiberg, Einar, 1973-
(författare)
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Efficient representations in matlab made easy - a tensor array toolbox
- 2001
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Ingår i: Proceedings of Nordic Matlab Conference, 2001. ; , s. 213-216
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Konferensbidrag (refereegranskat)abstract
- Tensors can be used to create efficient and intuitive representations for a wide variety of applications, including signal and image processing, mechanics and fluid dynamics. In order to achieve this in Matlab, a toolbox was developed designed to enhance Matlab's ability to store and manipulate arrays, such that each element in the array can be vectors or general tensors. This paper describes the implementation of the tool box and gives several examples on the usage of tensor representations for signal and image processing. Furthermore, the representation and processing of uncertain data using tensor representations is described as well.
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- Janerot-Sjöberg, Birgitta, 1958-, et al.
(författare)
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Influence of respiration on myocardial signal intensity
- 2001
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Ingår i: Ultrasound in Medicine and Biology. - 0301-5629 .- 1879-291X. ; 27:4, s. 473-479
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Tidskriftsartikel (refereegranskat)abstract
- Echocardiographic quantification of myocardial perfusion after IV contrast is possible, based on the intensity of the received intermittent second harmonic signal. To investigate the influence of respiration on the intensity of myocardial signals, we examined nine patients with normal coronary angiograms. At baseline, end-expiratory and end-inspiratory images were obtained in broadband radiofrequency (RF) and intermittent second harmonic modes, the latter repeated during IV contrast at rest and at peak stress. In mid-septum at baseline, end-inspiratory integrated backscatter intensity was 4 dB higher (p < 0.05, both in second harmonic and fundamental domains) than end-expiratory intensity. In second harmonic imaging, contrast increased signal intensity by 4 dB (p < 0.05) in six examined segments, but the increase in the midseptal region (2 dB) was not significant. Contrast-enhanced intensity at end-inspiration was higher (3 dB, p < 0.01) than baseline intensity at end-expiration. We conclude that the increase in myocardial signal intensity during inspiration may resemble the contrast effect in intermittent second harmonic mode. The respiratory variation persists after contrast and may mask or exaggerate the effect of myocardial contrast.
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- Pislaru, Cristina, et al.
(författare)
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Is there a change in myocardial nonlinearity during the cardiac cycle?
- 2001
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Ingår i: Ultrasound in Medicine and Biology. - 0301-5629 .- 1879-291X. ; 27:3, s. 389-398
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Tidskriftsartikel (refereegranskat)abstract
- The distortion of a sound wave during propagation results in progressive transfer of the energy from fundamental to higher harmonics, and is dependent on the nonlinearity of the medium. We studied if relative changes in acoustical nonlinearity occur in healthy myocardium during the cardiac cycle. Radiofrequency data were acquired from transthoracic echocardiography (2.5 and 3.5 MHz), parasternal long axis view, from five dogs and nine healthy volunteers. Integrated backscatter was calculated after filtering for fundamental (FIB) and second harmonic frequencies (SHIB), from a region in the posterior myocardial wall. The results suggest that there is little difference between the SHIB and FIB, although there were large variations between individuals. The maximal changes in nonlinearity, as estimated by SHIB/FIB ratio, mostly occurred during systole. SHIB presented similar cyclic variation with FIB (p = NS). Further studies are necessary to separate the role of myocardial nonlinearity, attenuation, propagating distance, or acoustical properties of the blood. The results are important in further tissue characterization studies employing second harmonic data.
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