| 1. |
- Axmon, Joakim, et al.
(författare)
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A signal model adapted ESPRIT algorithm for joint estimation of spatial and temporal parameters in vibrational analysis of cylinders
- 2002
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Ingår i: 2002 IEEE Sensor Array and Multichannel Signal Processing Workshop Proceedings (Cat. No.02EX593). - 0780375513 ; , s. 360-364
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Konferensbidrag (refereegranskat)abstract
- This paper deals with the joint estimation of spatial mode shapes and temporal frequencies from transient vibrations measured by a uniform circular array of sensors encircling a cross-section of a cylinder. The geometry allows each 2D mode to be interpreted as two real planar waves impinging from mirrored directions with respect to the broadside of a uniform linear array. Algorithms for joint estimation tend, in the presence of noise, to produce signal roots that express planar waves impinging from only approximately mirrored directions. A recently published 2-D ESPRIT algorithm is modified to take advantage of the geometry, and to force the estimated planar waves to impinge from exactly mirrored directions. This reduces the estimation errors; the main advantage is more easily interpreted results. Memory requirements and complexity are significantly lower for the modified algorithm, since the decomposition of a large data matrix may be broken down into several small ones
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| 2. |
- Axmon, Joakim, et al.
(författare)
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Experimental study on the possibility of detecting internal decay in standing Picea abies by blind impact response analysis
- 2004
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Ingår i: Forestry. - : Oxford University Press (OUP). - 1464-3626 .- 0015-752X. ; 77:3, s. 179-192
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Tidskriftsartikel (refereegranskat)abstract
- This paper considers detection of internal decay in standing trees of species Picea abies (L.) Karst. The novel approach is based on two-dimensional spatiotemporal modal analysis of a cross-section which is excited by the hand-made impact of a hammer. An array of accelerometers is distributed around the cross-section, and the resulting impact response is analysed. The temporal frequency for a special spatial mode-shape is used for comparisons on a tree-to-tree basis. The mechanical properties of wood are inherently variable as they are for most materials of biological origin. This leads to a scatter of the analysed parameters that hinders detection of decay based on the temporal frequencies alone. Using regression analysis, we show that by incorporating the additional information on a surface wave propagation velocity, the scatter of sound trees is significantly reduced. The performance of a detector rule which incorporates the frequency and the surface wave propagation velocity is investigated and found to be better than performance reported for visual tree examination. The analyses are based on the impact responses from 94 standing trees, with 66 sound and 28 in various stages of decay. The proposed technique is yet to be considered an experimental tool. Further research, e.g. on how the mechanical properties are influenced by various environmental factors, is needed before the technique can be applied operationally.
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| 3. |
- Axmon, Joakim, et al.
(författare)
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Partial modal analysis for health assessment of living trees
- 2001
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Ingår i: Asia-Pacific conference on non-destructive testing (APCNDT).
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Konferensbidrag (refereegranskat)abstract
- Rot in living trees cause substantial losses for the forestry industry. The common practice when evaluating forest stands for, e.g., purchase, is assessment based on visual signs. In this paper a new non-destructive assessment method based on the impact excitation method is proposed. The trunk of a living tree is excited by the impact of a hammer, and the vibrations are measured by accelerometers. Resonance frequencies, circumferential mode shapes and propagation velocity of a surface wave are analysed. A function describing the expected frequency for a sound tree is derived, and used in a detector whose performance is evaluated for 93 trees of species Norway spruce. The partial mode shape is used to ensure that the corresponding resonance frequencies are compared to each other. It is found that the detector is successful and outperforms assessments by skilled experts in forestry.
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| 4. |
- Bennhagen, Rolf, et al.
(författare)
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High-frequency components in ECG analysed in guinea-pig Langendorf preparations
- 2001
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Ingår i: Clinical Physiology. - : Wiley. - 1365-2281 .- 0144-5979. ; 21:5, s. 576-583
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Tidskriftsartikel (refereegranskat)abstract
- High-frequency components in ECG during global ischaemia were studied in isolated guinea-pig hearts perfused ad modum Langendorf. Electrocardiograph recordings were carried out from the epicardial surface both in normo- and low-flow perfusion. After bandpass filtering (5-500 Hz), signal-averaging, was undertaken. The high-frequency components either increased or decreased after low-flow perfusion was instituted. Root-mean-square voltage (RMS) of the depolarization signal correlated poorly with the signal amplitude, but highly with the first and second derivative, i.e. the velocity and the acceleration of the signal. It is concluded that high-frequency components are not pathological phenomena per se, but reflect the shape of the original electrocardiographic signal.
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| 5. |
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| 6. |
- Bollmann, Andreas, et al.
(författare)
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Echocardiographic and electrocardiographic predictors for atrial fibrillation recurrence following cardioversion
- 2003
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Ingår i: Journal of Cardiovascular Electrophysiology. - : Wiley. - 1540-8167 .- 1045-3873. ; 14:s10, s. 162-165
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: Identification of suitable candidates for cardioversion currently is not based on individual electrical and mechanical atrial remodeling. Therefore, this study analyzed the meaning of atrial fibrillatory rate obtained from the surface ECG (as a measure of electrical remodeling) and left atrial size (as measure of mechanical remodeling) for prediction of early atrial fibrillation (AF) recurrence following cardioversion. Methods and Results: Forty-four consecutive patients (26 men and 18 women, mean age 62 ± 11 years, no antiarrhythmic medication at baseline) with persistent AF were studied. Fibrillatory rate was obtained from high-gain, high-resolution surface ECG using digital signal processing (filtering, QRST subtraction, Fourier analysis) before electrical cardioversion. Univariate and multivariate regression analysis revealed larger systolic left atrial area (Beta = 0.176, P = 0.031) obtained by precardioversion echocardiogram from the apical four-chamber view and higher atrial fibrillatory rate (Beta = 0.029, P = 0.021) to be independent predictors for AF recurrence (n = 13). Stratification based on the regression equation (electromechanical index [EMI]= 0.176 systolic left atrial area + 0.029 fibrillatory rate − 17.674) allowed identification of groups at low, intermediate, or high risk. No patient with an EMI < −1.85 had early AF recurrence, as opposed to 78% with an EMI > −0.25. Intermediate results (40% recurrence rate) were obtained when the calculated EMI ranged between −1.85 and −0.25 (P < 0.001). Conclusion: Fibrillatory rate obtained from the surface ECG and systolic left atrial area obtained by echocardiography may predict early AF recurrence in patients with persistent AF. These parameters might be useful in identifying candidates with a high likelihood of remaining in sinus rhythm after cardioversion.
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| 7. |
- Bollmann, A, et al.
(författare)
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Frequency measures obtained from the surface electrocardiogram in atrial fibrillation research and clinical decision-making
- 2003
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Ingår i: Journal of Cardiovascular Electrophysiology. - : Wiley. - 1540-8167 .- 1045-3873. ; 14:s10, s. 154-161
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Tidskriftsartikel (refereegranskat)abstract
- Frequency Measures in AF. Introduction: Frequency analysis of fibrillation (FAF) and time-frequency analysis (TFA) were developed recently in order to quantify atrial electrical remodeling in atrial fibrillation (AF) from the surface ECG. This article describes the experience with these two different frequency analysis techniques in consecutive AF patients and discusses possible applications in AF research and clinical decision-making. Methods and Results: Baseline 2-minute, high-gain, high-resolution ECG recordings using three bipolar leads were obtained from 80 consecutive patients with AF lasting >24 hours. A power spectrum was obtained using Fourier analysis following spatiotemporal QRST cancellation. The dominant fibrillatory rate (in fibrillations per minute [fpm]) was derived (FAF). Stability of the instantaneous fibrillatory rate measured in overlapping 1-second segments was expressed as the segment proportion with consecutive rate differences <6 fpm (TFA). An adequate power spectrum that could be submitted for determination of fibrillatory rate was obtained in all patients. Dominant atrial rates ranged between 288 and 534 fpm and showed a high correlation (R = 0.878-0.911, P < 0.001) when assessed from the three different leads. The average instantaneous fibrillatory rate was inversely related with its stability (R = -0.417, P < 0.001). It was closely related with the dominant fibrillatory rate obtained from FAF (R = 0.948, P < 0.001). A literature review revealed that pharmacologic or electrical cardioversion and AF pace termination success rates were highly dependent on fibrillatory rate. Conclusion: Atrial fibrillatory rate and its variability can be reliable obtained from the surface ECG in AF patients. These parameters exhibit a significant interindividual variability allowing individual quantification of the atrial electrical remodeling process and might prove useful for predicting therapy efficacy.
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| 8. |
- Garcia, J., et al.
(författare)
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Automatic detection of ST-T complex changes on the ECG using filtered RMS difference series: application to ambulatory ischemia monitoring
- 2000
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Ingår i: IEEE Transactions on Biomedical Engineering. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-2531 .- 0018-9294. ; 47:9, s. 1195-1201
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Tidskriftsartikel (refereegranskat)abstract
- A new detector is presented which finds changes in the repolarization phase (ST-T complex) of the cardiac cycle. It operates by applying a detection algorithm to the filtered root mean square (rms) series of differences between the beat segment (ST segment or ST-T complex) and an average pattern segment. The detector has been validated using the European ST-T database, which contains ST-T complex episodes manually annotated by cardiologists, resulting in sensitivity/positive predictivity of 85/86%, and 85/76%, for ST segment deviations and ST-T complex changes, respectively. The proposed detector has a performance similar to those which have a more complicated structure. The detector has the advantage of finding both ST segment deviations and entire ST-T complex changes thereby providing a wider characterization of the potential ischemic events. A post-processing stage, based on a cross-correlation analysis for the episodes in the rms series, is presented. With this stage subclinical events with repetitive pattern were found in around 20% of the recordings and improved the performance to 90/85%, and 89/76%, for ST segment and ST-T complex changes, respectively.
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| 9. |
- Garcia, J, et al.
(författare)
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ECG-based detection of body position changes in ischemia monitoring
- 2003
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Ingår i: IEEE Transactions on Biomedical Engineering. - 1558-2531. ; 50:6, s. 677-685
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this gaper is to analyze and detect changes in body position (BPC) during electrocardiogram (ECG) recording. These changes are often manifested as shifts in the, electrical axis and may be misclassified as ischemic changes during. ambulatory monitoring. We investigate two ECG signal processing methods for detecting BPCs. Different schemes for feature extraction are used (spatial and scalar), while preprocessing, trend postprocessing and detection are identical. The spatial approach is based on VCG loop rotation angles and the scalar approach is based on the Karhunen-Loeve transform (KLT) coefficients. The methods are evaluated on two different databases: a database with annotated BPCs and the STAFF III database with recordings from rest and during angioplasty-induced ischemia but not including BPCs. The angle-based detector results in performance values of detection probability P-D = 95%, false alarm probability P-F = 3% in the BPC database and false alarm rate in the STAFF III database in control ECCs during rest R-F(c) = 2 h(-1) (episodes per hour) and in ischemia recordings during angioplasty R-F(a) = 7 h(-1), whereas the KLT-based detector produces values of P-D = 89%, P-F = 3%, R-F(c) = 4 h(-1), and RF(a) = 11 h-1, respectively. Including information on noise level in the detection process to reduce the number of false alarms, performance values of P-D similar or equal to 90%, P-F similar or equal to 1%, R-F(c) similar or equal to 1 h(-1) and R-F(a) similar or equal to 2 h(-1) are obtained with both methods. It is concluded that reliable detection of BPCs may be achieved using the ECG signal and should work in parallel to ischemia detectors.
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| 10. |
- Garcia, J, et al.
(författare)
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Remote processing server for ECG-based clinical diagnosis support
- 2002
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Ingår i: IEEE Transactions on Information Technology in Biomedicine. - 1089-7771. ; 6:4, s. 277-284
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present the development of a remote server that provides a user-friendly access to advanced electrocardiographic (ECG) signal processing techniques. The prototype supplies telemedicine facilities to doctors for clinical indexes remote computation to support diagnosis through the Internet. The user-friendly interface is based on the selection of the desired ECG signal processing tools on a Web browser window. The centralized structure of the system permits unique and user-independent update and management of the software and, therefore, is especially suitable for remote or rural regions to have access to the new ECG information techniques.
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