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da Cruz Silva Andrade Madeira e Carvalho de Moura, Maria Margarida
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- Time-variable blood flow averaged waveformsPublication . Leiria, A.; da Cruz Silva Andrade Madeira e Carvalho de Moura, Maria Margarida; Evans, D. H.; Ruano, M. GraçaThe computation of the average of random signals is addressed in this article. These averaging techniques are particularly relevant for Doppler blood flow clinical evaluation and research that usually accesses clinical indicators related to maximum and mean frequency, bandwidth and power variation over time. A novel technique is presented and compared to one previously described in the literature (Kitney and Giddens, "Analysis of blood velocity waveforms by phase shift averaging and autoregressive spectral estimation'', J. Biomech. Eng., 105, 398 - 404, 1983.). While the latter method is an iterative one, which sometimes does not converge, the former is a sequential technique, guaranteeing convergence. Clinical Doppler blood flow signals were averaged using both methods and the resulting waveforms were evaluated against the original signals, emphasising the impact on the relevant spectral parameters. The results obtained showed that, except for the maximum error in the computation of power variation over time, the errors produced are reduced by the proposed new algorithm.
- Adaptive system for blood flow estimationPublication . da Cruz Silva Andrade Madeira e Carvalho de Moura, Maria Margarida; Leiria, A.; Ruano, M. GraçaAdaptive estimation of blood flow signals is performed resorting to a framework developed to support research on Doppler blood flow signals' analysis. Real time spectral estimation methods, real time performance evaluation and run-time adjustment of the estimation methods parameters are bound together allowing the system to adapt itself to varying signal characteristic that are caused by physiological reasons.
- Adaptive system for blood flow estimationPublication . da Cruz Silva Andrade Madeira e Carvalho de Moura, Maria Margarida; Leiria, A.; Ruano, M. GraçaAdaptive estimation of blood flow signals is performed resorting to a framework developed to support research on Doppler blood flow signals' analysis. Real time spectral estimation methods, real time performance evaluation and run-time adjustment of the estimation methods parameters are bound together allowing the system to adapt itself to varying signal characteristics that are caused by physiological reasons.
- Time, time-frequency and displacement-frequency analysis of embolic signalsPublication . Leiria, A.; da Cruz Silva Andrade Madeira e Carvalho de Moura, Maria Margarida; Ruano, M. Graça; Evans, D. H.The characteristics of a new method, the displacement-frequency representation, prompted the study of its use for the analysis of embolic blood flow signals. This paper reports the comparison of displacement-frequency and time-frequency methods with time domain methods, in the characterization of emboli. The study was performed on clinical signals derived from gaseous and particulate embolic events. The results obtained with the different approaches were compared. The conclusions of this study provide encouragement for the use of displacement-frequency domain processing for this kind of analysis.