Intrathecal morphine for coronary bypass grafting.
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Analgesia, Patient-Controlled↗
Biomedical subjects
V Dutt
Publications and source records attributed to V Dutt.
Acoustic shear-wave imaging using echo ultrasound compared to magnetic resonance elastography.
We compare a previously developed phase contrast-based magnetic resonance imaging technique (MRE) to a phase-based ultrasound (US) method for measuring small cyclic displacements (submicrometer level) caused by propagating acoustic shear waves in tissue-like media. Our preliminary experiments with gelatin phantoms show that acoustic shear-wave propagation can be measured with US, and we speculate that this technique could find applications in medical imaging.
Humans↗
Statistics of the log-compressed echo envelope.
Log compression of A lines to produce B-scan images in clinical ultrasound imaging systems is a standard procedure to control the dynamic range of the images. The statistics of such compressed images in terms of underlying scatterer statistics have not been derived. The statistics are analyzed for partially formed speckle using a general K distribution model of envelope statistics to derive the density function for the log-compressed envelope. This density function is used to elucidate the relation between the moments of the compressed envelope, the compression parameters, and the statistics of the scatterers. The analysis shows that the mean of the log-compressed envelope is an increasing function of both the backscattered energy and the effective scatterer density. The variance of the log-compressed envelope is a decreasing function of the effective scatterer density and is independent of the backscattered energy.
Computer Simulation↗
Speckle analysis using signal to noise ratios based on fractional order moments.
The SNR (signal-to-noise ratio) of the echo envelope image is a monotonically-increasing function of scatterer number density. Various SNRs, like amplitude SNR and intensity SNR, can be used to quantify the scatterer density. The problem of using a SNR based on higher order moments like the intensity SNR is that they require large sample sizes to obtain estimates with high confidence (the variance of the estimate becomes large for higher moments). In this paper, we consider SNRs based on fractional order moments (moments of order less than 1), and obtain mathematical analyses of their properties using the K distribution, which has been shown to be a good model for the density function of backscatter echo envelope signal. Statistics of SNRs based on fractional moment are derived and appear to be more robust and useful than the amplitude and intensity SNRs previously studied. The SNRs based on fractional order moments have greater dynamic range and the sample size requirements are smaller than those for integral order moment SNRs, like amplitude SNR or intensity SNR. Thus, SNRs based on fractional order moments could be used to better quantify the variations in scatterer density which can be used for tissue classification problems.
Humans↗
Ultrasound echo envelope analysis using a homodyned K distribution signal model.
The statistics of ultrasound echo envelope signals can be used to characterize scattering media. The Rayleigh distribution and its generalized forms, the K and Rice distributions, have been previously used to model the echo signal. A more generalized statistical model, the homodyned K distribution, combines the K and Rice distribution features to better account for the statistics of the echo signal. We show that this model can give two parameters that are useful for media characterization: k, the ratio of coherent to diffuse signals, and, beta, which characterizes the clustering of scatters in the medium.
Computer Simulation↗