| 1. |
- Janusauskas, Arturas, et al.
(författare)
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Detection of Hearing Loss in Audiological Frequencies from Transient Evoked Otoacoustic Emissions
- 2010
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Ingår i: Informatica. - 0868-4952. ; 21:2, s. 191-204
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Tidskriftsartikel (refereegranskat)abstract
- Transient evoked otoacoustic emissions (TEOAEs) have been analyzed for objective assessment of hearing function and monitoring of the influence of noise exposure and ototoxic drugs. This paper presents a novel application of the Hilbert-Huang transform (HHT) for detection and time-frequency mapping of TEOAEs. Since the HHT does not distinguish between signal and noise, it is combined with ensemble correlation in order to extract signal information in intervals with correlated activity. High resolution time-frequency mapping could predict 30 dB(HL), or higher hearing loss, at different audiological frequencies in 63-90% of the cases and normal hearing in 75-90% of the cases. The proposed method offers TEOAE time-frequency mapping by constraining the analysis to regions with high signal-to-noise ratios. The results suggest that the HI-IT is suitable for hearing loss detection at individual frequencies and characterization of the fine structures of TEOAEs.
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| 2. |
- Kvikliene, Adriana, et al.
(författare)
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Modelling of nonlinear effects and the response of ultrasound contrast micro bubbles : simulation and experiment
- 2004
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Ingår i: Ultrasonics. - : Elsevier BV. - 0041-624X .- 1874-9968. ; 42:01-Sep, s. 301-307
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Tidskriftsartikel (refereegranskat)abstract
- The propagation of diagnostic ultrasonic imaging pulses in tissue and their interaction with contrast micro bubbles is a very complex physical process, which we assumed to be separable into three stages: pulse propagation in tissue, the interaction of the pulse with the contrast bubble, and the propagation of the scattered echo. The model driven approach is used to gain better knowledge of the complex processes involved. A simplified way of field simulation is chosen due to the complexity of the task and the necessity to estimate comparative contributions of each component of the process. Simulations are targeted at myocardial perfusion estimation. A modified method for spatial superposition of attenuated waves enables simulations of low intensity pulse pressure fields from weakly focused transducers in a nonlinear, attenuating, and liquid-like biological medium. These assumptions enable the use of quasi-linear calculations of the acoustic field. The simulations of acoustic bubble response are carried out with the Rayleigh-Plesset equation with the addition of radiation damping. Theoretical simulations with synthesised and experimentally sampled pulses show that the interaction of the excitation pulses with the contrast bubbles is the main cause of nonlinear scattering, and a 2-3 dB increase of second harmonic amplitude depends on nonlinear distortions of the incident pulse. (C) 2004 Elsevier B.V. All rights reserved.
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| 3. |
- Marozas, Vaidotas, et al.
(författare)
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Multiscale detection of transient evoked otoacoustic emissions
- 2006
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Ingår i: IEEE Transactions on Biomedical Engineering. - 1558-2531. ; 53:8, s. 1586-1593
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a unified approach to multiscale detection of transient evoked otoacoustic emissions (TEOAEs). Using statistical detection theory, it is shown that the optimal detector involves a time windowing operation where the window can be estimated from ensemble correlation information. The detector performs adaptive splitting of the signal into different frequency bands using either wavelet or wavelet packet decomposition. A simplified detector is proposed in. which signal energy is omitted. The results show that the simplified detector performs significantly better than existing TEOAE detectors based on wave reproducibility or the modified variance ratio, whereas the. detector involving signal energy does not offer such a performance advantage.
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| 4. |
- Petrenas, Andrius, et al.
(författare)
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A noise-adaptive method for detection of brief episodes of paroxysmal atrial fibrillation
- 2013
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Ingår i: 2013 Computing in Cardiology. - 9781479908844 ; 40, s. 739-742
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Konferensbidrag (refereegranskat)abstract
- The aim of this work is to develop a method for detection of brief episode paroxysmal atrial fibrillation (PAF). The proposed method utilizes four different features: RR interval irregularity, absence of P waves, presence of f-waves and noise level. The obtained features are applied to the Mamdani-type fuzzy inference method for decisionmaking. The performance was evaluated on one hundred 90 s long surrogate ECG signals with brief PAF episodes (5-30 beats). The robustness to noise in ECGs where noise level in each set is incremented in steps of 0.01 mV from 0 to 0.2 mV was examined as well. When compared to the coefficient of sample entropy, our method showed considerably better performance for low and moderate noise levels (< 0.06 mV) with an area under the receiver operating characteristic curve of 0.9 and 0.94, respectively. Similar performance is expected for higher noise levels as atrial activity is less used in the detection process. Finally, the results suggest that our method is more robust to false alarms due to ectopic beats or other irregular rhythms than the method under comparison.
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| 5. |
- Petrenas, Andrius, et al.
(författare)
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An Echo State Neural Network for QRST Cancellation During Atrial Fibrillation
- 2012
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Ingår i: IEEE Transactions on Biomedical Engineering. - 1558-2531. ; 59:10, s. 2950-2957
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Tidskriftsartikel (refereegranskat)abstract
- A novel method for QRST cancellation during atrial fibrillation (AF) is introduced for use in recordings with two or more leads. The method is based on an echo state neural network which estimates the time-varying, nonlinear transfer function between two leads, one lead with atrial activity and another lead without, for the purpose of canceling ventricular activity. The network has different sets of weights that define the input, hidden, and output layers, of which only the output set is adapted for every new sample to be processed. The performance is evaluated on ECG signals, with simulated f-waves added, by determining the root mean square error between the true f-wave signal and the estimated signal, as well as by evaluating the dominant AF frequency. When compared to average beat subtraction (ABS), being the most widely used method for QRST cancellation, the performance is found to be significantly better with an error reduction factor of 0.24-0.43, depending on f-wave amplitude. The estimates of dominant AF frequency are considerably more accurate for all f-wave amplitudes than the AF estimates based on ABS. The novel method is particularly well suited for implementation in mobile health systems where monitoring of AF during extended time periods is of interest.
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| 6. |
- Petrenas, Andrius, et al.
(författare)
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Detection of occult paroxysmal atrial fibrillation
- 2015
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Ingår i: Medical & Biological Engineering & Computing. - : Springer Science and Business Media LLC. - 0140-0118 .- 1741-0444. ; 53:4, s. 287-297
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Tidskriftsartikel (refereegranskat)abstract
- This work introduces a novel approach to the detection of brief episodes of paroxysmal atrial fibrillation (PAF). The proposed detector is based on four parameters which characterize RR interval irregularity, P-wave absence, f-wave presence, and noise level, of which the latter three are determined from a signal produced by an echo state network. The parameters are used for fuzzy logic classification where the decisions involve information on prevailing signal quality; no training is required. The performance is evaluated on a large set of test signals with brief episodes of PAF. The results show that episodes with as few as five beats can be reliably detected with an accuracy of 0.88, compared to 0.82 for a detector based on rhythm information only (the coefficient of sample entropy); this difference in accuracy increases when atrial premature beats are present. The results also show that the performance remains essentially unchanged at noise levels up to RMS. It is concluded that the combination of information on ventricular activity, atrial activity, and noise leads to substantial improvement when detecting brief episodes of PAF.
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| 7. |
- Petrenas, Andrius, et al.
(författare)
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Reservoir computing for extraction of low amplitude atrial activity in atrial fibrillation
- 2012
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Ingår i: 2012 Computing in Cardiology. - 9781467320740 ; 39, s. 13-16
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Konferensbidrag (refereegranskat)abstract
- A novel method for QRST cancellation during atrial fibrillation (AF) is introduced for use in recordings with two or more leads. The method is based on an echo state neural network (ESN) which estimates the time-varying, nonlinear transfer function between two leads, one lead with atrial activity and another lead without, for the purpose of canceling ventricular activity. The performance is evaluated on ECG signals, with simulated f-waves of low amplitude added, by determining the root mean square error P between the true f-wave signal and the estimated signal, as well as by evaluating the dominant AF frequency. When compared to average beat subtraction (ABS), being the most widely used method for QRST cancellation, the performance is found to be significantly better with equal to mean and standard deviation of PESN 24.8±7.3 and PABS 34.2±17.9 μV (p < 0.001). The novel method is particularly well-suited for implementation in mobile health systems where monitoring of AF during extended time periods is of interest.
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| 8. |
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| 9. |
- Ressner, Marcus, 1967-, et al.
(författare)
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Ultrasound contrast for perfusion studies
- 2005
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Ingår i: Nordic Baltic Conference Biomedical Engineering and Medical Physics,2005. - Umeå : IFMBE. ; , s. 107-
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Konferensbidrag (refereegranskat)
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| 10. |
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