Tukey Window Research Articles

Abstract 271: Continuous Amplitude Spectral Area May Reflect Adequacy of Myocardial Perfusion Before Attempting Defibrillation

Background: Previous studies have shown that analysis of the VF amplitude-spectral area (AMSA) contains information predictive of electrical shock success. However, the underlying factors that determine AMSA remain elusive. We developed an open-chest swine model of VF in which we modeled “average CPR” followed by “highly effective CPR” using extracorporeal circulation (ECC) and assessed AMSA in relation to adequacy of coronary perfusion. Methods: VF was electrically induced and left untreated for 8 min in 8 pigs after which ECC was started and maintained for 10 min adjusting the flow to generate a coronary perfusion pressure (CPP) of 10 mmHg (low-flow ECC). After delivery of an initial shock, the ECC flow was increased and titrated to secure a mean aortic pressure of 40 mmHg (high-flow ECC) delivering additional electrical shocks at 60 s intervals. Blood flow through the left anterior descending (LAD) artery was reported relative to baseline (LAD rel). AMSA was measured continuously with a 2.1 s timeframe and a Tukey window that moved ahead every 0.5 s, and was averaged every min for this report (Figure). Results: AMSA increased during the initial 5 min of low-flow ECC, but subsequently decreased (Figure). The initial shock uniformly failed to terminate VF prompting increases in ECC to high-flow, which then resulted in the return of spontaneous circulation in each instance after 3 to 5 shocks. During the high-flow ECC, AMSA initially increased but then gradually decreased for reasons that are not clear. Before attempting defibrillation, AMSA was positively correlated with LAD rel (r=0.73, p=0.04). Conclusion: The study provides intriguing data showing changes in AMSA that are time dependent and likely influenced by myocardial perfusion and the effects of electrical shocks on the myocardium. The present study also suggests that the level of AMSA prior to attempting defibrillation may be influenced by the efficacy with which the CPR intervention generates coronary blood flow.

A Proposed Method to Measure Sub Pixel Shift in Egyptsat-1 Aliased Images

This paper presents a method for image-based shift measurement and investigates solution for the mismatched bands of egyptsat-1 satellite. A tiny error in measuring sub pixel shift leads to an incorrect image focusing. Different methods, using frequency approach are conducted with different Tukey window sizes for measuring the sub pixel shift. The present method use an aim to select most important frequency for three parameter; horizontal, vertical and rotation with different window size. To test the present method; we used the SPOT-5 satellite data with known displacement. The obtained results are acceptable, and might solve Egyptsat-1 problem of mismatches between its bands. Bands 1, 2 could also be used in super resolution reconstruction methods General Terms Image processing, Remote sensing

Is hands-on defibrillation safe when using insulating gloves? A clinical trial

Introduction: Surface electrocardiographic (ECG) changes in ventricular fibrillation (VF) waveform characteristics at its onset in patients experiencing cardiac arrest have not been quantified. The amplitude spectral area (AMSA)methodwas developed to analyze surface ECG VF amplitude and frequency characteristics and contains information related to VF rotor stability and myocardial viability. We aimed to characterize changes in AMSA at the onset of VF to gain insight into myocardial dynamics in patients with a wearable cardioverter defibrillator (WCD). Methods: Out of 30 patients randomly identified from a manufacturer-maintained registry, 25 patients (14 Male, 11 Female, Age=62±14 yr) were included. Remaining patients experienced either sustained monomorphic ventricular tachycardia or hadmotion artifact, precludingAMSAanalysis. Using theWCDECG, AMSA was calculated as the summed product of frequency and square root of power at that frequency from 2 to 48Hz with a continuous sliding 2.1 s Tukey window. The median time to shock for the WCD is 45 s. AMSA was calculated every 0.5 s and averaged every 1 s for up to 45 s after VF initiation. Results are presented as mean± standard error. Results: At onset of VF, AMSA was 33.6±3.3mVHz which decreased progressively to 23.4±2.2mVHz (p<0.01) after 45 sec of untreated VF (Fig. 1).

Abstract 73: Changes in AMSA During Controlled Coronary Perfusion by Extracorporeal Circulation in a Swine Model of Ventricular Fibrillation

Background: Previous VF studies in rats showed that 6 min of CPR was needed before an electrical shock could be successful in reestablishing cardiac activity. During this interval the amplitude spectral area (AMSA) - a method of VF waveform analysis - progressively rose reaching a plateau within the same interval required for enabling successful defibrillation. No previous studies have examined AMSA continuously using a model of tightly controlled CPR. Methods: VF was induced and left untreated for 8 min in 16 swine after which extracorporeal circulation (ECC) was maintained for 10 min adjusting its flow to generate a coronary perfusion pressure of 10 mmHg. AMSA was calculated from the VF signal in the frequency domain within 2-48 Hz and analyzed continuously with a 2.1 s timeframe and a Tukey window that moved ahead every 0.5 s. Results: AMSA progressively declined during untreated VF. During ECC, AMSA rose from 6.8±1.9 to 12.4±4.1 mV*Hz (p&lt;0.001). The increase occurred early during ECC and plateaued after 4 to 6 minutes (Figure). Individual experiments showed distinct and varying AMSA patterns during ECC. The average peak AMSA was reached 368 ± 127 s after the start of ECC. Conclusion: The time course of AMSA varied among animals suggesting variability in the time required for the myocardium to reach the optimal conditions for successful defibrillation and highlights the value of continuous monitoring of AMSA during CPR.

Effects of wideband source types on accuracy of wideband path-loss prediction based on finite-difference time-domain scheme

The finite-difference time-domain (FDTD) scheme is a well-known numerical algorithm that can solve a wideband response of a wave equation in time domain. When the FDTD scheme is applied to the problem of the underwater path-loss, however, the wideband source excitation may generate various problems at low frequency band. For instance, when a source is implemented with a large magnitude near the zero frequency, a spurious response can be generated in the FDTD simulation due to the DC component that cannot propagate. On the other hand, when a source is implemented with very small magnitude at low frequencies, the numerical accuracy cannot be guaranteed. In this work, implementation of a new wideband source for FDTD scheme is proposed that is suitable for response over a wide bandwidth, including very low frequencies. The Tukey window is applied to a wideband Gaussian pulse in the frequency domain, which eliminates the DC component effectively. By utilizing the steep slope of a Tukey window, higher accuracy is achieved in the low frequencies. To verify the proposed wideband source, the path-loss results based on the FDTD scheme are compared with the famous normal mode solution, KRAKEN, as well as the ray solution, BELLHOP.

Optimization of the window function for digital hologram apodization in reconstructing the holographic image

In this paper, an optimal window function used for digital hologram apodization in reconstructing the holographic image is presented, which is generated by a cosine window convolving with a rectangle window and has a flat top because of the rectangle shape of the hologram. The window’s parameters are optimized using a genetic algorithm to make sure that the sidelobes of the window are minimum. Numerical simulation results show that the new window has a sidelobe lower than that of the Tukey window, and experimental results show that apodization using this window can suppress the diffraction effectively in reconstructing the holographic image.

Enhanced ultrasound strain imaging using chirp-coded pulse excitation

To improve the quality of ultrasound strain imaging, chirp-coded pulse excitation which can enhance echo signal-to-noise ratio (eSNR) was used. The effects of various factors on chirp-coded strain imaging were investigated. Five chirp schemes were designed to investigate the relationship of the range side lobe level (RSLL), main lobe width and energy for strain imaging. We use phase zero method with amplitude modulation correction as strain estimator. The simulation results demonstrate that elastographic signal-to-noise ratio (SNRe) for chirp pulse decreases with the RSLL and the main lobe width, and that there is a tradeoff among choosing a high-energy tapering window function, reducing the RSLL and narrowing the main lobe in designing a chirp scheme for strain imaging. Chirp pulse performs much better than conventional short pulse in low eSNR, great depth or high attenuation conditions due to the increased eSNR with it. However, in high eSNR condition, the increased eSNR with chirp pulse does not improve SNRe, and the performance of chirp pulse mainly depends on the RSLL and main lobe width. Some chirp schemes still achieve higher SNRe than short pulse in high eSNR condition, because these chirp schemes have narrower main lobe than short pulse and have very low RSLL. Chirp pulse has better lesion detectability and axial strain resolution than short pulse especially in low eSNR condition, because chirp pulse can use shorter window length to get the same SNRe that is achieved by short pulse. Within the scope of five window functions (Tukey, Lanczos, Parzen, Dolph–Chebyshev and Kaiser), we tried to find the optimal chirp scheme which is possibly the combination of chirp pulse excitation with 40% tapered Tukey window and matched compression filter. A commercial elastic phantom experiment on a freehand strain imaging system further validates the superior performance of chirp pulse.

Keyhole Imaging기법을 적용한 위상대조도 자기공명 혈관조영기법

Phase Contrast MR Angiography(PC MRA) is excellent MRA technique for measuring the velocity of vessels in the human body. PC MRA need to at least four images for angiogram reconstruction and it caused longer scan time. Therefore, we used keyhole imaging combined PC MRA to reduce the scan time. However, keyhole imaging can lead the erroneous effects as loss of phase information or frequency discontinuous. In this study, we applied the keyhole imaging combined 2D PC MRA for improving the temporal resolution and also measured the velocity to evaluate the accuracy of phase information. We used 0.32T MRI scanner(Magfinder II, Scimedix, Korea). Using the 2D PC MRA pulse sequence, the vascular images for a human brain targeted on the Superior Sagittal Sinus(SSS) were obtained. We applied tukey window function for keyhole images to minimize the ringing artifact and erroneous factors that are induced frequency discontinuous and phase information loss. We also applied zero-padded algorithm to peripheral missing k-space lines to compare keyhole imaging results and the artifact power(AP) value was measured on the complex difference images to validate the image quality. Consider as based on our results, heavy image distortions and artifacts were shown until using at least 50% keyhole factor. Using above the 50% keyhole factors are shown well reconstructed and matched for magnitude images and velocity information measurements. In conclusion, we confirmed the image quality and velocity information of keyhole technique combined 2D PC MRA. Especially, measured velocity information through the keyhole imaging combination was similar to the velocity information of full sampled k-space image despite of frequency discontinuous and phase information loss in the keyhole imaging reconstruction process. Consequently, the keyhole imaging combined 2D PC MRA will give some clinical usefulness and advantages as improving the temporal resolution and measuring the velocity information via selecting the appropriate keyhole factor at low tesla MRI system.

An Efficient Approach for Time-Domain Simulation of Pulse Propagation in Optical Fiber

A novel approach is proposed for split-step time-domain simulation of pulse propagation in optical fiber. In this approach, a Fourier series expansion method is introduced for time-domain digital filter extraction from any given fiber transfer function. With such extracted filter coefficients and a double Tukey window function, the filter length can be optimized for a given error tolerance. This method is validated by comparing our simulation results with that obtained from the well-known split-step frequency-domain method. Through several simulation examples, we find that this solution technique is much more efficient than other existing time-domain approaches-as much as 92% of the computation time can be saved. It even outperforms the well-known split-step frequency-domain fast Fourier transform method in terms of the computation efficiency, under the condition that the input signal samples are huge-a situation we often meet in dealing with wavelength division multiplexing systems. Moreover, we find that the truncation effect at the computation window edge introduced by the time-domain algorithm is less severe than the aliasing effect associated with the frequency-domain method, not to mention that we can eliminate the truncation error by using a sliding window, only at a small cost on computation time.

Photoacoustic tomography in absorbing acoustic media using time reversal

The reconstruction of photoacoustic images typically neglects the effect of acoustic absorption on the measured time domain signals. Here, a method to compensate for acoustic absorption in photoacoustic tomography is described. The approach is based on time-reversal image reconstruction and an absorbing equation of state which separately accounts for acoustic absorption and dispersion following a frequency power law. Absorption compensation in the inverse problem is achieved by reversing the absorption proportionality coefficient in sign but leaving the equivalent dispersion parameter unchanged. The reconstruction is regularized by filtering the absorption and dispersion terms in the spatial frequency domain using a Tukey window. This maintains the correct frequency dependence of these parameters within the filter pass band. The method is valid in one, two and three dimensions, and for arbitrary power law absorption parameters. The approach is verified through several numerical experiments. The reconstruction of a carbon fibre phantom and the vasculature in the abdomen of a mouse are also presented. When absorption compensation is included, a general improvement in the image magnitude and resolution is seen, particularly for deeper features.

Elliptical-Tukey Chirp Signal for High-Resolution, Air-Coupled Ultrasonic Imaging

A new signal processing method, which uses a modified chirp signal for air-coupled ultrasonic imaging, is described. A combination of the elliptical and Tukey window functions has been shown to give a better performance than the Hanning windowing used in most pulse-compression algorithms for air-coupled applications. The elliptical-Tukey chirp signal provides an improvement in both the resolution of images and signal-to-noise ratios. In addition, this type of signal also reduces the level of signal voltages required to drive the source transducer while maintaining the performance of the system. This approach, thus, may have wide interest in all forms of wide bandwidth ultrasonic imaging.

Fault detection in induction motors using Hilbert and Wavelet transforms

In this work, a new on-line method for detecting incipient failures in electrical motors is proposed. The method is based on monitoring certain statistical parameters estimated from the analysis of the steady state stator current (for broken bars, saturation, eccentricities, and bearing failures) or the axial flux signal (for coil short-circuits in the stator windings). The approach is based on the extraction of the envelop of the signal by Hilbert transformation, pre-multiplied by a Tukey window to avoid transient distortion. Then a wavelet analysis (multi-resolution analysis) is performed, which makes the fault diagnosis easier. Finally, based on a statistical analysis, the failure thresholds are determined. Thus, by monitoring the mean value estimate it is possible to detect an incipient failure condition on the machine.

Decreased coherence in higher frequency ranges (beta and gamma) between central and frontal EEG in patients with schizophrenia: A preliminary report

Schizophrenia is associated with a dysfunction of cognitive integration that may be due to abnormalities in inhibitory neural circuitry. A previous study found a failure of gamma band (25–45 Hz) synchronization in patients with schizophrenia compared to controls. Another recent study also stressed the importance of investigating high frequencies in the scalp-recorded sleep electroencephalogram (EEG). In this study, we compared coherence between first episode drug-naïve patients with schizophrenia ( n = 8) and age- and sex-matched normal controls ( n = 8) using two 32-s epochs of C4 and F4 EEG. The coherence was obtained using 4096 data points (128 Hz signal) using cross-spectral analysis with Blackman–Tukey window in beta (15.25–24.75 Hz) and gamma (25–44.75 Hz) frequency bands. We used wake, non-rapid eye movement (NREM) and rapid eye movement (REM) sleep periods for the analyses. Our results show a significant decrease in coherence in both beta and gamma frequency bands in patients. Post-hoc ‘ t’ tests revealed a significantly lower coherence only during the wake stage in patients with schizophrenia in beta as well as gamma frequency bands. These results further support the importance of the analyses of high-frequency bands in the EEG and support previous findings of abnormal neural synchrony in patients with schizophrenia. These results have been discussed further in relation to wake and sleep stages.

An Accurate Transient Analysis of High-Speed Package Interconnects Using Convolution Technique

An accurate transient analysis of a package interconnect requires the modeling and analysis of conductor and dielectric losses, as well as other high-frequency effects of 3D structures. The skin effect and dispersion of interconnects are more accurately modeled in frequency domain. Consequently, an accurate time-domain simulation of such a system is only possible using convolution techniques. Although the convolution method is well understood, the application of windowing for frequency-dependent interconnect analysis is less so. In this paper, we present the practical considerations of window selection and its application to improve the accuracy of convolution simulators. We introduce the Tukey window and study the tradeoff between how smoothly data can be set to zero to avoid aliasing and suppress ripples and how much information tapering will discount at the edge of the window in order to obtain meaningful results. The bandlimiting effects of the Tukey window and other well-known windows are also compared. Finally, to verify the validity and accuracy of the proposed method, a wirebond PBGA package and a PCB-connector system are analyzed using the scattering parameters obtained from simulation and measurement, respectively.

Digital signal processing for precision wide-swath bathymetry

A mathematical model is formulated which accurately represents the envelope function of bottom return signals received from a number of spatial directions comprising a wide swath. The bottom return signals are processed utilizing a digital nonrecursive matched filter whose coefficients are tapered using a Tukey window. High-speed convolution employing the fast Fourier transform is examined for implementation of the digital matched filtering operation. Computer simulation of the signal processing system indicates that, even in the presence of considerable background and fluctuation noises, the processor provides an output signal having a well-defined peak. The error in time of arrival is found to be less than 3 ms, corresponding to an error in depth of less than 0.1 percent, for an average signal-to-noise ratio of 15 dB and a vertical ocean depth of 12 000 ft (3.7 km). These performance figures apply to the most difficult case of mapping at angles of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\pm 45\deg</tex> off vertical.

Some novel windows and a concise tutorial comparison of window families

Some novel windows are introduced. A comparison of these and the well-known windows in terms of their frequency domain properties is given. It is concluded that Kaiser, modified Kaiser, Tukey, and three-coefficient window families appear to be the best of the known windows of 6, 12, and 18 dB/oct decay rates.

Planetary Pressure Wave of 4- to 5-Day Period in the Tropics

Surface pressure data during the Inter- employed. The phase spectrum shows that the 4 to national Geophysical Year period for 76 stations in the 5-day oscillations result from a westward moving wave tropical zone 20°N-200S have been examined to investi- having a periodicity of 4-5 days and wave number 1. gate the propagation characteristics, if any, of the 4- to The direction of propagation is identical in both hemi- 5-day pressure oscillations. Cross-spectrum analysis with spheres and shows no inclination to latitude circles. a first-difference filter and the Tukey window has been In a recent paper, Misra (1971) presented evidence for the global scale of an atmospheric pressure oscillation of 4- to 5-day periodicity. A plot of the phase difference against the longitude difference for stations arranged in zonal belts demonstrates the existence of a westward propagating wave having periodicity of 4-5 days and wave number 1. The wave was earlier evidenced in an analysis by Wallace and Chang (1969), who used data for a few stations north of the Equator. The present paper examines more closely the behavior of this wave propagation in the tropical zone 20°N-200S.