| 1. |
- Floreby, L, et al.
(författare)
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Boundary finding using Fourier surfaces of increasing order
- 1998
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Ingår i: Proceeedings of the Fourteenth International Conference on Pattern Recognition. - 1051-4651. - 0818685123 ; 1, s. 465-467
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Konferensbidrag (refereegranskat)abstract
- Boundary finding in simulated medical images is performed by optimizing the Fourier coefficients in a parametric surface representation with respect to an objective function. The deformable model is fitted to the data using the brightness gradient component which is normal to the surface. A low order (<10) Fourier series expansion offers a sufficiently accurate representation for many inherently smooth objects that occur in medical imaging. Experimental results are presented for simulated image objects corresponding to organs of the anthropomorphic Zubal phantom. Two different optimization methods are studied concerning robustness and computational efficiency. The effect of increasing the Fourier expansion order is investigated for various noise levels
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| 2. |
- Floreby, L, et al.
(författare)
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Deformable Fourier surfaces for volume segmentation in SPECT
- 1998
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Ingår i: Proceeedings of the Fourteenth International Conference on Pattern Recognition. - 1051-4651. - 0818685123 ; 1, s. 358-360
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Konferensbidrag (refereegranskat)abstract
- Three-dimensional boundary finding based on Fourier surface optimization is presented as a method for segmentation of SPECT images. Being robust against noise and adjustable with respect to its detail resolution, it forms an interesting alternative in this application area. A three-dimensional approach can also be assumed to increase the possibility of delineating low contrast regions, as compared to a two-dimensional slice-by-slice approach. We apply boundary finding to Monte Carlo simulated SPECT images of the computer-based anthropomorphic Zubal phantom in order to evaluate the influence of object contrast and noise on the segmentation accuracy. Segmentation is also performed in real patient images
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| 3. |
- Holm, Magnus, et al.
(författare)
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Non-Invasive Assessment of the Atrial Cycle Length during Atrial Fibrillation in Man: Introducing, Validating and Illustrating a New ECG Method
- 1998
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Ingår i: Cardiovascular Research. - 1755-3245. ; 38:1, s. 69-81
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES: Atrial fibrillation (AF) in man has previously been shown to include a wide variety of atrial activity. Assessment of the characteristics of this arrhythmia with a commonly applicable tool may therefore be important in the choice and evaluation of different therapeutic strategies. As the AF cycle length has been shown to correlate locally with atrial refractoriness and globally with the degree of atrial organization, with, in general, shorter cycle length during apparently random AF compared to more organized AF, we have developed a new method for non-invasive assessment of the AF cycle length using the surface and the esophagus (ESO) ECG. METHODS AND RESULTS: From the frequency spectrum of the residual ECG, created by suppression of the QRST complexes, the dominant atrial cycle length (DACL) was derived. By comparison with multiple intracardiac simultaneously acquired right and left AF cycle lengths in patients with paroxysmal AF, we found that the DACL in lead V1, ranging from 130 to 185 ms, well represented a spatial average of the right AF cycle lengths, whereas the DACL in the ESO ECG, ranging from 140 to 185 ms, reflected both the right and the left AF cycle length, where the influence from each structure depended on the atrial anatomy of the individual, as determined by MRI. In patients with chronic AF, the method was capable of following changes in the AF cycle length due to administration of D,L-sotalol and 5 min of ECG recording was sufficient for the DACL to be reproducible. CONCLUSIONS: We conclude that this new non-invasive method, named 'Frequency Analysis of Fibrillatory ECG' (FAF-ECG), is capable of assessing both the magnitude and the dynamics of the atrial fibrillation cycle length in man.
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| 4. |
- Holm, Magnus, et al.
(författare)
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Non-Invasive Assessment of the Atrial Cycle Length during Chronic Atrial Fibrillation in Man
- 1996
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Ingår i: 69th Scientific Sessions of the American Heart Association, New Orleans, November 10-13, 1996; Circulation, Vol. 94, No. 8 Suppl., pp. I69, 1996.. ; 94, s. 169-169
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Konferensbidrag (refereegranskat)
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| 5. |
- Meurling, Carl, et al.
(författare)
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Attenuation of electrical remodelling in chronic atrial fibrillation following oral treatment with verapamil
- 1999
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Ingår i: Europace. - : Oxford University Press (OUP). - 1532-2092 .- 1099-5129. ; 1:4, s. 234-241
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Tidskriftsartikel (refereegranskat)abstract
- AIMS: Electrical remodelling with shortening of the atrial refractory period and increased fibrillatory rate occurs after onset of atrial fibrillation and can be attenuated by pre-treatment with intravenous verapamil. The aim of the present study was to investigate whether already established fibrillatory-induced shortening of atrial fibrillatory cycle length could be reversed with oral verapamil. METHODS AND RESULTS: Thirteen patients (nine men; mean age 67 years) with chronic atrial fibrillation (CAF) were studied. The dominant atrial cycle length (DACL) was estimated non-invasively using the frequency analysis of fibrillatory ECG (FAF-ECG) method. Measurements were repeated following treatment with slow release oral verapamil. DACL increased from 147 +/- 13 ms to 156 +/- 21 ms after 1 day (P=0.02), to 164 +/- 18 ms after 5 days (P=0.005) and finally to 160 +/- 16 ms after 6 weeks (P=0.008). CONCLUSION: Long-term oral treatment with verapamil increases the DACL significantly in patients with CAF. The prolongation is evident after 1 day and is further developed during the first 5 days of treatment. Since DACL is believed to be an index of refractoriness, the findings of the present study suggest that this treatment increases the atrial refractory period in patients with CAF.
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| 7. |
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| 8. |
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| 9. |
- Pehrson, Steen, et al.
(författare)
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Non-invasive assessment of magnitude and dispersion of atrial cycle length during chronic atrial fibrillation in man
- 1998
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Ingår i: European Heart Journal. - : Oxford University Press (OUP). - 1522-9645 .- 0195-668X. ; 19:12, s. 1836-1844
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Tidskriftsartikel (refereegranskat)abstract
- AIMS: Atrial fibrillation cycle lengths can be assessed from right precordial ECG leads and the unipolar oesophageal ECG using a non-invasive method called Frequency Analysis of Fibrillatory ECG. The purpose of this report is to present the results from application of this method in a large group of patients with long-term atrial fibrillation and to examine the differences between patients with 'coarse' and 'fine' atrial fibrillation. METHODS AND RESULTS: Simultaneous 15 min recordings from V1, V2 and an oesophageal lead at a position behind the posterior atrium were obtained in 28 patients, aged 41 to 78 years, with long-term (> 1 month) atrial fibrillation. In each lead, using the time averaging technique, the QRST complexes were suppressed. Thereafter, the frequency distribution of the residual ECG was estimated by means of Fast Fourier Transform. In the 3-12 Hz range of each lead, the dominant atrial cycle length, the power maximum and the spectral width were calculated. In 26 patients (93%), frequency spectra in the 3-12 Hz range could be obtained. The dominant atrial cycle length ranged from 120 to 175 ms, mean 150+/-16 (SD) ms in V1, and from 120 to 190 ms, mean 150+/-16 in an oesophageal lead (ns). The absolute difference in the dominant atrial cycle length between V1 and the oesophageal lead was 10.4+/-7.7 ms. There was no significant difference in the dominant atrial cycle length in V1 between patients with coarse and fine atrial fibrillation. The power maximum in V1 was significantly greater in patients with coarse compared to fine atrial fibrillation (P=0.01). The spectral widths ranged from 10 to 55 ms and demonstrated significantly higher mean values in lead V2 compared to V1 (P=0.001). Compared to V1, the mean values tended to be smaller in the oesophageal lead (P=0.05). CONCLUSIONS: Using the Frequency Analysis of Fibrillatory ECG method, the dominant atrial cycle length, power maximum and spectral width can be estimated from the frequency spectra in the majority of patients with atrial fibrillation. Spatial dispersion of the dominant atrial cycle length occurs in some patients and may be an important proarrhythmic marker. The distinction between coarse and fine atrial fibrillation cannot be used as a marker of the atrial cycle length.
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