Browsing by Author "Fish, P. J."
Now showing 1 - 7 of 7
Results Per Page
Sort Options
- A spectral estimator using parallel-processing for use in a doppler blood-flow instrumentPublication . 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.
- Alternative parallel implementations of an AR-modified covariance spectral estimator for diagnostic ultrasonic blood flow studiesPublication . 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 the algorithm into a number of tasks were considered - a fine and a medium grain task scheme. The medium grain scheme is mapped onto a transputer-based system, by means of a processor farm computational structure. Two approaches to this farm model were adopted: a linear and a tree topology. For different model parameters, performance measurements were obtained revealing that the tree topology offers a higher performance. © 1993.
- Cost-benefit selection of spectral estimators for use with ultrasonic doppler blood-flow intrumentsPublication . Ruano, M. Graça; Fish, P. J.
- Cost/benefit criterion for selection of pulsed Doppler ultrasound spectral mean frequency and bandwidth estimatorsPublication . 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. | 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.
- Nonstationarity broadening reduction in pulsed Doppler spectrum measurements using time-frequency estimatorsPublication . 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 duration of 10 ms for the SFTF, 40 ms for the WVD and CWD and 20 ms for the BD and dimensionless time-frequency smoothing constant values of five in the CWD and two in the BD. Thresholding was used to reduce the effect of cross terms and side lobes in the WVD and BD. With no added noise the WVD gave the lowest estimation error followed by the CWD. At signal-to-noise ratios (SNR's) of 10 dB and 20 dB the CWD and BD had similar errors and were markedly better than the other estimators. Overall the CWD gave the best performance.
- Parallel implementation of a Choi-Williams TFD for Doppler signal analysisPublication . Cardoso, J. C.; Fish, P. J.; Ruano, M. GraçaThe spectral width and mean frequency of Doppler signals is used to measure and characterise lesion-induced flow disturbance. Conventional methods of spectral estimation based on the Fourier Transform compromise the measurement accuracy since these methods implicitly assume signal stationarity during the signal window under analysis. New methods based on Time-Frequency Distribution (TFD), especially developed for non-stationary signal analysis, are now being introduced which avoid these limitations, at the cost of an increase in the computation burden required. This paper describes the parallel implementation of one TFD method, the Choi-Williams Distribution (CWD), in a transputer platform with 5 processors. The goal is to obtain a real time spectral analyser.
- Parallel implementation of a model-based spectral estimator for Doppler blood flow instrumentationPublication . 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 pulsed Doppler blood flow instrumentation.