SVD-based on-line exercise ECG signal orthogonalization

Cataloged from PDF version of article.An orthogonalization method to eliminate unwanted signal components in standard 12-lead exercise electrocardiograms (ECG’s) is presented in this work. A singular-valuedecomposition-based algorithm is proposed to decompose the signal into two time-orthogonal subspaces; one containing the ECG and the other containing artifacts like baseline wander and electromyogram. The method makes use of redundancy in 12- lead ECG. The same method is also tested for reconstruction of a completely lost channel. The online implementation of the method is given. It is observed that the first two decomposed channels with highest energy are sufficient to reconstruct the STsegment and J-point. The dimension of the signal space, on the other hand, does not exceed three. Data from 23 patients, with duration ranging from 9 to 21 min, are used

VLSI Circuits for adaptive digital beamforming in ultrasound imaging

Cataloged from PDF version of article.For phased-array ultrasound imaging, alternative beamforming techniques and their VLSI circuits are studied to form a fully digital receive frontad hardware. In order to increase the timiig accuracy in beamforming, a computationally efficient interpolation scheme to increase the sampling rate is examined. For adaptive beamforming, a phase aberration correction method with very low computational complexity is described. Image quality performance of the method is examined by processing the non-aberrated and aberrated phased-array experimental data sets of an ultrasound resolution phantom. A digital beamforming scheme based on receive focusing at the raster focal points is examined. The sector images of the resolution phantom, reconstructed from the phased-array experimental data by beamforming at the radial and raster focal points, are presented for comparison of the image resolution performances of the two beamforming schemes. VLSI circuits and their implementations for the proposed techniques are presented

Rayleigh-Bloch waves in CMUT arrays

Cataloged from PDF version of article.Using the small-signal electrical equivalent circuit of a capacitive micromachined ultrasonic transducer (CMUT) cell, along with the self and mutual radiation impedances of such cells, we present a computationally efficient method to predict the frequency response of a large CMUT element or array. The simulations show spurious resonances, which may degrade the performance of the array. We show that these unwanted resonances are due to dispersive Rayleigh-Bloch waves excited on the CMUT surface-liquid interface. We derive the dispersion relation of these waves for the purpose of predicting the resonance frequencies. The waves form standing waves at frequencies where the reflections from the edges of the element or the array result in a Fabry-Pérot resonator. High-order resonances are eliminated by a small loss in the individual cells, but low-order resonances remain even in the presence of significant loss. These resonances are reduced to tolerable levels when CMUT cells are built from larger and thicker lates at the expense of reduced bandwidth. © 2014 IEEE

Equivalent Circuit-Based Analysis of CMUT Cell Dynamics in Arrays

Cataloged from PDF version of article.Capacitive micromachined ultrasonic transducers (CMUTs) are usually composed of large arrays of closely packed cells. In this work, we use an equivalent circuit model to analyze CMUT arrays with multiple cells. We study the effects of mutual acoustic interactions through the immersion medium caused by the pressure field generated by each cell acting upon the others. To do this, all the cells in the array are coupled through a radiation impedance matrix at their acoustic terminals. An accurate approximation for the mutual radiation impedance is defined between two circular cells, which can be used in large arrays to reduce computational complexity. Hence, a performance analysis of CMUT arrays can be accurately done with a circuit simulator. By using the proposed model, one can very rapidly obtain the linear frequency and nonlinear transient responses of arrays with an arbitrary number of CMUT cells. We performed several finite element method (FEM) simulations for arrays with small numbers of cells and showed that the results are very similar to those obtained by the equivalent circuit model

Distribution of aortic mechanical prosthetic valve closure sound model parameters on the surface of chest

Cataloged from PDF version of article.It has been previously proposed that heart valve closure sounds can be modeled by a sum of decaying sinusoids, based on the hypothesis that the heart cavity, heart walls, major vessels, and other structures in the chest constitute a frequency selective linear acoustic system and this system is excited by the rapidly decelerating valve occluder. In this study, distribution of the parameters of this model for the second heart sound is investigated. For this purpose, heart sounds of 10 patients who have a St. Jude-type bileaflet mechanical heart valve prosthesis in aortic position are recorded. Recordings are performed at 12 different locations on the surface of the chest. To reliably assign representative parameters to each recording site, signal averaging, model order selection, and a special filtration technique are employed. The results of the analyses are discussed in relation to the above hypothesis on the heart sound generation mechanism. It is observed that site-to-site variation of frequencies of modes does not exceed the accuracy limit of proposed analysis method, but energies of these modes vary on the surface of the chest, and as a result of statistical analysis, it appears that energy of some modes are significantly different between two recording sites

A phase aberration correction method for ultrasound imaging

Cataloged from PDF version of article.A computationally efficient method for phase aberration correction in ultrasound imaging is presented. The method is based on time delay estimation via minimization of the sum of absolute differences between radio frequency samples of adjacent array elements. Effects of averaging estimated aberration patterns over scan angles, and truncation to a single bit wordlength are examined. Phase distortions due to near-field inhomogeneities are simulated using silicone rubber aberrators. Performance of the method is tested using experimental data. Simulation studies addressing different factors affecting efficiency of the method, such as the number of iterations, window length, and the number of scan angles used for averaging, are presented. Images of a standard resolution phantom are reconstructed and used for qualitative testing

A Spectrally efficient PMR System Utilizing Broadcast Service

Cataloged from PDF version of article.Different trunked Private Mobile Radio (PMR) systems have been designed over the last several decades, all of which have symmetric downlink and uplink channel capacities. Due to this symmetry, these systems may not be spectrally efficient in case of different types of services, which are specific to PMR systems, such as group and broadcast calls. In this study, a new asymmetric trunked PMR system comprising a broadband, wide-area downlink and a narrowband cellular uplink, is proposed to achieve a higher spectral efficiency than current digital trunked PMR systems. This system is spectrally more efficient because in group and broadcast calls only a single downlink channel has to be allocated in the downlink part. However, as the number of clusters in the system increases, this advantage relative to PMR systems is lost, since the latter can employ frequency reuse. Spectral efficiency of the proposed asymmetric system (a-PMR) system and a standard TETRA system are compared using numerical case studies against different traffic loads and number of clusters. The optimum point, with respect to number of clusters, up to which the proposed a-PMR system is more efficient, is determined. It is shown that a very large PMR user population can be efficiently served using the proposed a-PMR system. The issues related to implementing such a system are discussed

Radiation Impedance of Collapsed Capacitive Micromachined Ultrasonic Transducers

Cataloged from PDF version of article.The radiation impedance of a capacitive micromachined ultrasonic transducer (CMUT) array is a critical parameter to achieve high performance. In this paper, we present a calculation of the radiation impedance of collapsed, clamped, circular CMUTs both analytically and using finite element method (FEM) simulations. First, we model the radiation impedance of a single collapsed CMUT cell analytically by expressing its velocity profile as a linear combination of special functions for which the generated pressures are known. For an array of collapsed CMUT cells, the mutual impedance between the cells is also taken into account. The radiation impedances for arrays of 7, 19, 37, and 61 circular collapsed CMUT cells for different contact radii are calculated both analytically and by FEM simulations. The radiation resistance of an array reaches a plateau and maintains this level for a wide frequency range. The variation of radiation reactance with respect to frequency indicates an inductance-like behavior in the same frequency range. We find that the peak radiation resistance value is reached at higher kd values in the collapsed case as compared with the uncollapsed case, where k is the wavenumber and d is the center-to-center distance between two neighboring CMUT cells