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Wang L.,Xiamen University | Li X.,Xiamen University | Chen Y.,Xiamen University | Qin J.,Shenzhen University | Qin J.,Guangdong Key Laboratory for Biomedical Measurements and Ultrasound Imaging
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2015

Inverse problem of electrocardiography (ECG) has been extensively investigated as the estimated epicardial potentials (EPs) reflecting underlying myocardial activities. Traditionally, L2-norm regularization methods have been proposed to solve this ill-posed problem. But L2-norm penalty function inherently leads to considerable smoothing of the solution, which reduces the accuracy of distinguishing abnormalities and locating diseased regions. Directly using L1-norm penalty function, however, may greatly increase the computational complexity due to its non-differentiability. In this study, we present a smoothed L0 norm technique in order to directly solve the L0 norm constrained problem. Our method employs a smoothing function to make the L0 norm continuous. Extensive experiments on various datasets, including normal human data, isolated canine data, and WPW syndrome data, were conducted to validate our method. Epicardial potentials mapped during pacing were also reconstructed and visualized on the heart surface. Experimental results show that the proposed method reconstructs more accurate epicardial potentials compared with L1 norm and L2 norm based methods, demonstrating that smoothed L0 norm is a promising method for the noninvasive estimation of epicardial potentials. © Springer International Publishing Switzerland 2015. Source

Dan G.,Shenzhen University | Dan G.,Guangdong Key Laboratory for Biomedical Measurements and Ultrasound Imaging | Dan G.,National Reginoal Key Technology Engineering Laboratory for Medical Ultrasound | Liu Z.-W.,South China University of Technology | And 2 more authors.
Gaoya Wuli Xuebao/Chinese Journal of High Pressure Physics | Year: 2015

The particle and stability properties of phosphatides dispersions affected by pulsed electric field, ultrasound, microfluid were studied using dynamic light scattering techniques. Results indicate that the average diameter of phosphatides particles decrease from 594.4 nm to 259.2, 88.7, 37.8 nm after being treated by 60 kV/cm pulsed electric field, 500 W ultrasound and 130 MPa microfluid, respectively. As for the stability of the treated phosphatides dispersion, it is demonstrated that the ultrasound treated sample is the most stable one, then following microfluid and pulsed electric field treated samples. ©, 2015, Chinese Journal of High Pressure Physics. All right reserved. Source

Guo L.,Chinese Academy of Sciences | Guo L.,University of Chinese Academy of Sciences | Guo L.,China University of Petroleum - East China | Liu G.-Q.,Chinese Academy of Sciences | And 3 more authors.
Chinese Physics B | Year: 2014

Conductivities tomography with the interactions of magnetic field, electrical field, and ultrasound field is presented in this paper. We utilize a beam of ultrasound in scanning mode instead of the traditional ultrasound field generated by point source. Many formulae for the reconstruction of conductivities are derived from the voltage signals detected by two electrodes arranged somewhere on tissue's surface. In a forward problem, the numerical solutions of ultrasound fields generated by the piston transducer are calculated using the angular spectrum method and its Green's function is designed approximately in far fields. In an inverse problems, the magneto - acousto - electrical voltage signals are proved to satisfy the wave equations if the voltage signals are extended to the whole region from the boundary locations of transducers. Thus the time-reversal method is applied to reconstructing the curl of the reciprocal current density. In addition, a least square iteration method of recovering conductivities from reciprocal current densities is discussed. © 2014 Chinese Physical Society and IOP Publishing Ltd. Source

Li J.,Shenzhen University | Li J.,Chinese University of Hong Kong | Zhou Y.,Shenzhen University | Zhou Y.,National Regional Key Technology Engineering Laboratory for Medical Ultrasound | And 3 more authors.
Ultrasonics | Year: 2015

Abstract Muscle force output is an essential index in rehabilitation assessment or physical exams, and could provide considerable insights for various applications such as load monitoring and muscle assessment in sports science or rehabilitation therapy. Besides direct measurement of force output using a dynamometer, electromyography has earlier been used in several studies to quantify muscle force as an indirect means. However, its spatial resolution is easily compromised as a summation of the action potentials from neighboring motor units of electrode site. To explore an alternative method to indirectly estimate the muscle force output, and with better muscle specificity, we started with an investigation on the relationship between architecture dynamics and force output of triceps surae. The muscular architecture dynamics is captured in ultrasonography sequences and estimated using a previously reported motion estimation method. Then an indicator named as the dorsoventrally averaged motion profile (DAMP) is employed. The performance of force output is represented by an instantaneous version of the rate of force development (RFD), namely I-RFD. From experimental results on ten normal subjects, there were significant correlations between the I-RFD and DAMP for triceps surae, both normalized between 0 and 1, with the sum of squares error at 0.0516±0.0224, R-square at 0.7929±0.0931 and root mean squared error at 0.0159±0.0033. The statistical significance results were less than 0.01. The present study suggested that muscle architecture dynamics extracted from ultrasonography during contraction is well correlated to the I-RFD and it can be a promising option for indirect estimation of muscle force output. © 2015 Elsevier B.V. Source

Dai P.,University of Toronto | Dai P.,A+ Network | Rudzicz F.,University of Toronto | Rudzicz F.,A+ Network | And 6 more authors.
Signal Processing | Year: 2015

Noise robustness has long been one of the most important goals in speech recognition. While the performance of automatic speech recognition (ASR) deteriorates in noisy situations, the human auditory system is relatively adept at handling noise. To mimic this adeptness, we study and apply psychoacoustic models in speech recognition as a means to improve robustness of ASR systems. Psychoacoustic models are usually implemented in a subtractive manner with the intention to remove noise. However, this is not necessarily the only approach to this challenge. This paper presents a novel algorithm which implements psychoacoustic models additively. The algorithm is motivated by the fact that weak sound elements that are below the masking threshold are the same for the human auditory system, regardless of the actual sound pressure level. Another important contribution of our proposed algorithm is a superior implementation of masking effect. Only those sounds that fall below the masking threshold are modified, which better reflects physical masking effects. We give detailed experimental results showing relationships between the subtractive and additive approaches. Since all the parameters of the proposed filters are positive or zero, they are named 2D psychoacoustic P-filters. Detailed theoretical analysis is provided to show the noise removal ability of these filters. Experiments are carried out on the AURORA2 database. Experimental results show that the word recognition rate using our proposed feature extraction method has been effectively increased. Given models trained with clean speech, our proposed method achieves up to 84.23% word recognition on noisy data. © 2015 Elsevier B.V. All rights reserved. Source

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