Recursos de colección
Sapientia Repositório Institucional Universidade do Algarve (30.790 recursos)
O Repositório Institucional da Universidade do Algarve desenvolvido no âmbito do projecto RCAAP.
Authenticus-118
O Repositório Institucional da Universidade do Algarve desenvolvido no âmbito do projecto RCAAP.
Authenticus-118
Cardoso, José C.; Ruano, M. Graça; Fish, Peter
The performances of various time-frequency distribution (TFD) methods in the estimation of mean frequency and spectral bandwidth of the nonstationary Doppler blood flow signal are compared using simulated signals with known characteristics and different signal to noise ratios.
Cardoso, José C.; Fish, Peter J.; Ruano, M. Graça
We apply a selection criterion for Doppler spectral estimators that takes into account the accuracy of the estimation, benefit, and also the `cost' in computation power required. This cost/benefit criterion is used to compare four time-frequency distributions (TFD) including the conventional short-term Fourier transform (STFT).
Ruano, M. Graca; Duarte, H. Simões; Teixeira, C. A.
Aiming at time-spatial characterization of tissue temperature when ultrasound is applied for thermal therapeutic proposes two experiments were developed considering gel-based phantoms, one of them including an artificial blood vessel. The blood vessel was mimicking blood flow in a common carotid artery. For each experiment phantoms were heated by a therapeutic ultrasound (TU) device emitting different intensities (0.5, 1, 1.5, 1.8 W/cm2). Temperature was monitored by thermocouples and estimated through imaging ultrasound transducer's signals within specific special points inside the phantom. The temperature estimation procedure was based on temporal echo-shifts (TES), computed based on echo-shifts collected through image ultrasound (IU)...
Ruano, Mg; Garcia, Df; Fleming, Pj; Fish, Pj
Ruano, M. Graça; Fish, P. J.
IEEE, Signal Proc. Soc.
Ruano, M. Graça; Nocetti, D. F. G.; Fish, P. J.; Fleming, P. J.
The work described here is part of a research program aiming to increase the sensitivity to disease detection using Doppler ultrasound by reducing the effects to the measurement procedure on the estimation of blood velocity and detection of flow disturbance.
Ruano, M. Graça; Fish, P. J.
A flexible selection criterion for spectral estimators based on the weighted statistical accuracy (benefit) of estimation of decisive spectral parameters under the constraint of low computational complexity (cost) is proposed. This new cost/benefit criterion also selects the model order for parametric spectral estimators - selecting model orders significantly lower than those determined by accepted criteria. The importance of different Doppler signal parameters (e.g., mean frequency and spectral bandwidth) and their accuracy of estimation is incorporated by the use of weighting factors. The use of this method with simulated Doppler signals led to the selection of the modified covariance Alt estimator....
Ruano, M. Graça; Nocetti, D. F. G.; Fish, P. J.; Fleming, P. J.
The work described here is part of a research program aiming to increase the sensitivity to desease detection using Doppler ultrasound by reducing the effects of the measurement procedure on the estimation of blood velocity and detection of flow disturbance. The paper presents a summary of autoregressive spectral estimation, focusing the attention on a specific estimator - the modified covariance method. This method has been realized in parallel to achieve a fast computer processing. The new parallel version of this algorithm has been developed and implemented on a multiprocessing transputer-based system. Two different approaches to the problem of parallel partitioning...
Nocetti, D. F. Garcia; Ruano, M. Graça; Fish, P. J.; Fleming, P.J.
This work presents a parallel implementation of a model-based spectral estimation method, based on the modified covariance parametric algorithm. This method has been implemented in order to take advantage of its resolution benefits when it is applied to spectral estimation in Doppler blood flow instrumentation. As the algorithm is computationally intensive and must be executed in realtime, parallel processing techniques have been utilized. Two different approaches are presented, these being implemented on a transputer-based system. Performances analysis of these approaches is presented together with concluding remarks. The results are being applied in the development of a real-time spectrum analyzer for...
Kiss, L.; Varkonyi-koczy, A. R.; Ruano, M. Graça
The main problem to be solved for autonomous indoor robots is that the environment where they have to move safety is only partially known and possibly dynamically changing. In this paper a hybrid navigation method is proposed, using two techniques that deal with a priori information and sensory data separately, thus blending the intelligence and optimality of global navigation methods with the reactivity and low complexity of local ones. The first, global navigation module, based on a priori information, chooses intermediary goals for the local navigation module, for which the so called A* algorithm is used. The second part, carrying...
Madureira, G.; Ruano, A. E.; Ruano, M. Graça
This study describes the on-line operation of a seismic detection system to act at the level of a seismic station providing similar role to that of a STA /LTA ratio-based detection algorithms. The intelligent detector is a Support Vector Machine (SVM), trained with data consisting of 2903 patterns extracted from records of the PVAQ station, one of the seismographic network's stations of the Institute of Meteorology of Portugal (IM). Records' spectral variations in time and characteristics were reflected in the SVM input patterns, as a set of values of power spectral density at selected frequencies. To ensure that all patterns...
Zabihian, B.; Ruano, M. Graça
Doppler Ultrasound (DU) blood flow signals, particularly when collected under intra-operative conditions are noisy; accurate extraction of clinical parameters from their spectra becomes a difficult task. The spectral center frequency and bandwidth were estimated using two estimators with alternative time-frequency resolutions: a fixed resolution method, the Short-Time Fourier Transform (STFT) and the multi-resolution Continuous Wavelet Transform (CWT). Their performance was also assessed when the DU signals were pre-processed by a recently proposed Noise Cancellation Technique (NCTech). The NCTech algorithm enables quantification of the magnitude of the canceled noise in the form of percentage, called Cancellation Level (CL). Quantitative comparisons have...
Zabihian, B.; Ruano, M. Graça; Gonzalez, J. S.; Nocetti, D. F. G.; Cruz, M. F.
This paper presents some practical issues regarding the development of a dedicated Doppler Ultrasound system (DUS) for the assessment of blood flow signal on coronary grafts during heart surgery. The DUS is composed of several processing units. This paper concentrates on front-end units: the transducer and a particular issue of the software interface for clinical evaluation, the noise cancellation technique (NCTech). The experimental set-up implemented to evaluate the transducer response is presented. The procedure employed to eliminate the noise components embedded in the DUS data is described. Each of these units was primarily tested in laboratory. Results show their effectiveness...
Zabihian, B.; Teixeira, C. A.; Ruano, M. Graça
Doppler ultrasound (DU) automatic detection of clinically relevant blood flow spectral parameters may be a difficult task when the spectrogram is corrupted with different types of noise. This paper introduces a technique to eliminate the spectrogram background noise without damaging the blood flow signals' content. Tests were performed on simulated signals with known spectral characteristics. Different signal to noise ratios were tested. Results of 100 signals were averaged. Based on the STFT spectrogram the center frequency and bandwidth of the simulated noisy signals were computed and evaluated against the deterministic curve. Results obtained by defining the background area of DU...
Várkonyi-kóczy, Ar; Ruano, G
Anytime signal processing algorithms are to improve the overall performance of larger scale embedded digital signal processing (DSP) systems. In such systems there are cases where due to abrupt changes within the environment and/or the processing system temporal shortage of computational power and/or loss of some data may occur. It is an obvious requirement that even in such situations the actual processing should be continued to insure appropriate performance. This means that signal processing of somewhat simpler complexity should provide outputs of acceptable quality to continue the operation of the complete embedded system. The accuracy of the processing will be...
Rövid, A.; Várkonyi-kóczy, A. R.; Ruano, M. Graça
Corner detection plays an important role in computer vision as well as in 3D reconstruction of a scene. With the help of the corners we can determine the most characteristic points of an object and so reconstruct them. Corners are useful in case of pattern recognition, as well. In this paper a new corner detection scheme is introduced which is based on fuzzy reasoning and applies a special local structure matrix. ©2004 IEEE.
Ruano, M. Graça; Moura, M. M. M.; Leiria, A.; Garcia, F.; Moreno, E.
A framework to support research and clinical applications on ultrasound Doppler blood flow signals' analysis was created by integration of several subsystems into a portable computer application. Several alternatives of the different subsystems were integrated allowing the comparison amongst them. Aiming initially the study of carotid artery blood flow signals, the framework is being extended to encompass different vases -such as the mean cerebral artery - and some cardiac valves -such as the aortic and mitral valves. Developed upon Debian Linux distribution, but portable to other operating systems, the application components considered were built from open source software.
Rovid, A.; Varkonyi-koczy, A. R.; Ruano, M. Graça; Varlaki, P.; Michelberger, P.
Car body deformation modeling plays a very important role in crash accident analyses, as well as in safe car body design. The determination of the energy absorbed by the deformation and the corresponding Energy Equivalent Speed can be of key importance, however their precise determination is a very difficult task. Although, using the results of crash tests, intelligent and soft methods offer a way to model the crash process itself, as well as to determine the absorbed energy, the before-crash speed of the car, etc. In this paper a modeling technique and an intelligent expert system are introduced which together...
Leiria, A; Ruano, Mg; Evans, Dh
This paper reports a novel method for representing the spectrum of pulsed Doppler ultrasound blood flow signals. It is an alternative to the time-frequency estimation method, that maintains the information contained in the time signal using a minimum computational cost solution.
Cardoso, J. C. S.; Ruano, M. Graça; Fish, P. J.
The spectral width of Doppler signals is used as measure of lesion-induced flow disturbance. Its estimation accuracy is compromised using the conventional short-term Fourier transform (STFT) since this method implicitly assumes signal stationarity during the signal window while the Doppler signals from arteries are markedly nonstationary. The Wigner-Ville (WVD), Choi-Williams (CWD) and Bessel distributions (BD), specifically designed for nonstationary signals, have been optimized for spectral width estimation accuracy and compared to the STFT under different signal to noise ratios using simulated Doppler signals of known time-frequency characteristics. The optimum parameter values for each method were determined as a Hanning window...